Foot (ft) - Unit Information & Conversion

Quick Answer

What is a foot? A foot (ft) is a unit of length equal to exactly 12 inches or 0.3048 meters. It's the primary human-scale measurement in the United States, used universally to describe people's height (5'10"), room dimensions (12' × 15'), and building layouts. Uniquely, feet are also the global standard for aviation altitude—pilots worldwide report altitude in feet regardless of their country's measurement system.

Quick Comparison Table

Feet	Meters	Inches	Yards	Common Example	Convert Now
1 ft	0.305 m	12 in	0.333 yd	Length of a standard ruler	Convert feet to meters
3 ft	0.914 m	36 in	1 yd	Height of a kitchen counter	Convert feet to inches
5 ft	1.524 m	60 in	1.667 yd	Height of a short adult	Convert meters to feet
6 ft	1.829 m	72 in	2 yd	Height of a tall person	Convert feet to yards
10 ft	3.048 m	120 in	3.333 yd	Height of a basketball hoop	Convert inches to feet
100 ft	30.48 m	1,200 in	33.3 yd	Length of a tennis court	Convert feet to cm

Definition

The foot is a unit of length in the British imperial and United States customary systems of measurement. Since the international yard and pound agreement of 1959, one foot has been defined as exactly 0.3048 meters, which equals precisely 12 inches or 1/3 of a yard.

The foot is denoted by the symbol ft or by a single prime mark ′ (e.g., 6′ means 6 feet). When combined with inches, the notation uses both symbols: 5′-9″ means 5 feet, 9 inches (69 inches total, or approximately 1.75 meters).

The foot occupies a unique position in the imperial system as the most commonly used length unit for human-scale measurements—distances that relate directly to human body size, living spaces, and immediate environments. While inches handle smaller precision work and miles cover long distances, feet describe the comfortable middle ground of everyday human experience.

History

The foot represents one of humanity's oldest measurement units, with origins predating written records.

Ancient Origins: The foot concept emerged independently in multiple ancient civilizations, all based on the approximate length of a human foot. The Egyptian royal cubit (20.6 inches) divided into smaller units approximating foot measurements. The Greek pous measured roughly 11.6 inches, while the Roman pes (foot) standardized at approximately 11.65 modern inches (296 mm).

Roman Influence: When Romans conquered Britain, they brought the pes, which heavily influenced British measurement traditions. The Roman foot divided into 12 unciae (inches), establishing the 12-inch relationship that persists today. Even after the Roman Empire fell, this measurement structure survived in English-speaking regions.

Medieval Variations: Throughout medieval Europe, foot measurements varied dramatically by region and ruler. Different "feet" existed simultaneously—the Tower foot, the London foot, and various guild-specific feet. King Henry I of England (r. 1100-1135) reportedly standardized the yard as the distance from his nose to his outstretched thumb, making the foot one-third of that distance.

Statute Definitions: In 1266, King Henry III's Composition of Yards and Perches defined relationships between feet, yards, and rods for land measurement. The 1324 statute by Edward II attempted further standardization, though regional variations persisted for centuries.

English Standardization: The British Weights and Measures Act of 1824 established the Imperial foot throughout the British Empire. This Imperial foot differed slightly from the US foot after American independence—the US maintained measurements from pre-1824 British standards.

1959 International Agreement: The international yard and pound agreement unified English-speaking countries. The United States, United Kingdom, Canada, Australia, New Zealand, and South Africa agreed that 1 yard equals exactly 0.9144 meters, making 1 foot exactly 0.3048 meters (304.8 mm). This ended over a century of slight differences between US and British feet.

US Survey Foot Retirement: From 1893 to 2023, the United States maintained two different feet—the international foot (0.3048 m exactly) and the US survey foot (0.30480061 m, or 1200/3937 meters). The survey foot was used for land surveys and mapping. On January 1, 2023, the National Geodetic Survey officially retired the US survey foot, making all American measurements use the international foot exclusively.

Aviation Standard: In 1947, the International Civil Aviation Organization (ICAO) standardized altitude measurements worldwide in feet. This remains universal today—even pilots in fully metric countries like France, Germany, and Japan report altitude in feet. This standardization prevents confusion and enhances safety in international aviation.

Real-World Examples

Human Height

The foot is the universal height measurement in the United States and remains common in the UK and Canada:

• 5'0″ (60 inches / 152 cm): Short adult, average 12-year-old child
• 5'4″ (64 inches / 163 cm): Average American woman
• 5'6″ (66 inches / 168 cm): Average worldwide male height
• 5'9″ (69 inches / 175 cm): Average American man
• 6'0″ (72 inches / 183 cm): Tall person, common for athletes
• 6'6″ (78 inches / 198 cm): Very tall, average NBA point guard
• 7'0″ (84 inches / 213 cm): Extremely tall, competitive advantage in basketball
• 7'4″+ (88+ inches / 224+ cm): Among tallest people, rare medical conditions

Americans describe height exclusively in feet and inches, never in total inches alone. Someone 69 inches tall would say "five-nine" (5'9″), not "sixty-nine inches." This convention creates instant understanding of human scale—hearing "six feet" immediately conveys "tall person."

Room Dimensions and Real Estate

Residential and commercial spaces in the US are universally described in feet:

• Bedroom (Small): 10' × 10' = 100 square feet
• Bedroom (Master): 14' × 16' = 224 square feet
• Living Room (Apartment): 12' × 18' = 216 square feet
• Living Room (House): 16' × 20' = 320 square feet
• Kitchen: 10' × 12' = 120 square feet (small), 12' × 16' = 192 sq ft (average)
• Bathroom: 5' × 8' = 40 square feet (powder room), 8' × 10' = 80 sq ft (full bath)
• Two-Car Garage: 20' × 20' = 400 square feet minimum
• Ceiling Height: 8 feet (standard), 9 feet (tall), 10+ feet (vaulted/luxury)

Real estate listings always show room dimensions in feet. Buyers instinctively understand these numbers—a 12' × 15' bedroom feels spacious, while a 10' × 10' feels cramped. Total home size uses square feet: 1,500 sq ft (small house), 2,500 sq ft (typical suburban home), 4,000+ sq ft (large/luxury home).

Sports Field Dimensions

American sports use feet for field specifications:

American Football:

• Field length: 360 feet (including end zones)
• Playing field: 300 feet (100 yards)
• Field width: 160 feet (53⅓ yards)
• Goal post height: 10 feet (crossbar), 35 feet total height
• First down marker: 30 feet (10 yards)

Basketball:

• Court length: 94 feet (NBA/college), 84 feet (high school)
• Court width: 50 feet
• Hoop height: 10 feet (rim above floor)
• Three-point line: 23.75 feet (NBA corner), 22 feet (college)
• Free throw line: 15 feet from backboard

Baseball:

• Base paths: 90 feet between bases (forming 90' × 90' diamond)
• Pitcher's mound distance: 60 feet, 6 inches from home plate
• Outfield fence: 300-400+ feet from home plate (varies by stadium)
• Foul poles: Often 300+ feet down lines

Tennis:

• Court length: 78 feet
• Singles width: 27 feet
• Doubles width: 36 feet
• Net height: 3 feet at center, 3.5 feet at posts

Aviation Altitude

Feet are the universal altitude measurement worldwide, regardless of country:

• Ground level: 0 feet MSL (Mean Sea Level)
• Pattern altitude: 1,000 feet AGL (Above Ground Level, typical small aircraft)
• Class B airspace: Typically surface to 10,000 feet near major airports
• Commercial cruising: 30,000-40,000 feet (FL300-FL400, "flight levels")
• Maximum Boeing 737: 41,000 feet ceiling
• Maximum Boeing 787: 43,000 feet ceiling
• Concorde cruise: 60,000 feet (supersonic passenger jet)
• U-2 spy plane: 70,000+ feet
• SR-71 Blackbird: 85,000+ feet

Flight levels above 18,000 feet use simplified notation: "FL350" means 35,000 feet. Pilots worldwide say "flight level three-five-zero" regardless of whether they're from metric or imperial countries. This universal standard prevents potentially deadly miscommunication during international flights.

Building Heights

Architectural height measurements use feet in the US:

• Single story: 10 feet (floor to floor, typical residential)
• Commercial story: 12-14 feet (floor to floor, office buildings)
• Two-story house: 20-24 feet (ground to roof peak)
• Three-story building: 30-36 feet
• Six-story building: 60-75 feet (typical older urban apartment building)
• Statue of Liberty: 305 feet (pedestal to torch)
• Seattle Space Needle: 605 feet
• Washington Monument: 555 feet
• Empire State Building: 1,250 feet (roof), 1,454 feet (with antenna)
• Willis Tower (Sears Tower): 1,450 feet (roof), 1,730 feet (with antennas)
• One World Trade Center: 1,776 feet (symbolic year of independence)

Building codes specify fire truck ladder reach and safety requirements in feet. Most fire department ladders reach 75-100 feet, influencing building safety design and fire codes.

Water Depth and Swimming Pools

Pool depths and water measurements use feet:

• Shallow end: 3-4 feet (standing depth for adults)
• Deep end (residential): 8-10 feet
• Diving pool minimum: 12 feet deep (for diving boards)
• Olympic diving platform: 33 feet above water (10 meters)
• Scuba certification depth: 60 feet (Open Water), 130 feet (Advanced)
• Recreational dive limit: 130 feet (without technical training)
• Lake depth typical: 20-60 feet (varies widely)
• Ocean shelf diving: 60-130 feet (recreational range)

US swimming pools always display depth markers in feet: "3 FT", "5 FT", "8 FT". Children learn to associate these numbers with safety—"stay in the 3-foot area if you can't swim."

Trees and Vegetation

Landscaping and forestry describe plant heights in feet:

• Shrub: 3-8 feet typical mature height
• Small ornamental tree: 10-15 feet
• Shade tree (young): 15-25 feet
• Mature shade tree: 40-80 feet (oak, maple, elm)
• Tall pines: 80-120 feet
• Coastal redwoods: 200-380 feet (tallest trees on Earth)
• Hyperion (tallest known tree): 380.3 feet (redwood in California)

Arborists, landscapers, and nurseries use feet for plant selection. A homeowner with 20-foot power line clearance knows to avoid trees that grow 40+ feet tall.

Fencing and Property Boundaries

Residential fencing and property work uses feet:

• Privacy fence height: 6 feet (standard)
• Picket fence height: 3-4 feet (decorative)
• Chain link fence: 4-6 feet (typical residential)
• Property line fence: 6-8 feet (maximum in most zoning codes)
• Lot width: 50-100 feet (typical suburban lot)
• Lot depth: 100-150 feet (typical suburban lot)
• Setback requirements: 10-25 feet from street (varies by zoning)

Property surveys, deed descriptions, and zoning regulations specify dimensions in feet. A typical lot description might read: "beginning at the northeast corner, thence 120 feet south, thence 80 feet west..."

Common Uses

Residential Construction and Remodeling

Home construction in America operates in feet for layout and square feet for area calculations. Foundation plans show exterior dimensions (e.g., 40' × 60' house footprint = 2,400 sq ft per floor). Interior walls use standard 8-foot studs for 8-foot ceiling heights, or 9-foot and 10-foot studs for taller ceilings.

Lumber lengths come in 2-foot increments: 6', 8', 10', 12', 14', 16' boards. This modular system allows efficient layout with minimal waste. A wall spanning 16 feet can use a single 16-foot top plate rather than joining shorter pieces.

Plywood and drywall sheets measure 4' × 8' (32 square feet per sheet). With standard 16-inch stud spacing, three studs span 48 inches (4 feet), perfectly matching sheet width. This dimensional coordination throughout the building industry stems from foot-based planning.

Standard door heights are 6'8" (80 inches), accommodating people up to about 6'5" with clearance. Door widths vary: 2'6" (30"), 2'8" (32"), 3'0" (36"). Window rough openings are specified in feet and inches: 3'0" × 4'0" window.

Architectural Design and Floor Plans

Architects draw floor plans at scales based on feet: 1/4" = 1'0" (common residential) or 1/8" = 1'0" (larger buildings). Blueprint dimensions appear as feet-inches notation: 12'-6" means 12 feet, 6 inches (150 inches total).

Room planning uses standard furniture dimensions understood in feet:

• Queen bed: approximately 5' × 6'8"
• King bed: approximately 6'4" × 6'8"
• Sofa: 6-8 feet long
• Dining table (seats 6): 3' × 6'
• Dining table (seats 8): 3'6" × 7'

Designers ensure adequate circulation space: 3 feet minimum for walkways, 4 feet preferred. A 12' × 15' bedroom comfortably fits a king bed with nightstands and leaves walkway space.

Building codes specify requirements in feet: egress windows must have 5.7 square feet of opening, stair landings must be at least 3 feet deep, hallways must be at least 3 feet wide.

Commercial Real Estate and Office Space

Commercial property leasing operates in square feet. Office space leases quote price per square foot annually: $30/sq ft/year means a 1,000 sq ft office costs $30,000 per year ($2,500/month). Retail space commands higher rates, often $40-100+/sq ft/year in prime locations.

Office planning uses square feet per employee: 150-250 sq ft per person including shared spaces, or 50-75 sq ft for individual workstations. A company with 50 employees needs approximately 7,500-12,500 square feet total.

Commercial buildings describe floor plate size in square feet: a 100' × 120' floor plate provides 12,000 sq ft of rentable space per floor. Column spacing (typically 20-30 feet in modern buildings) affects layout flexibility.

Retail space measures street frontage in feet—20 feet, 40 feet, 60 feet of storefront directly influences visibility and foot traffic. Corner locations with frontage on two streets command premium rent.

Swimming and Aquatics

Swimming pools use feet for all dimensions. A typical residential pool might measure 16' × 32' (512 sq ft surface area) with shallow end 3'6" and deep end 8'0". Lap pools are typically 8-10 feet wide by 40-50 feet long.

Competition pools follow precise foot-based specifications:

• Short course: 75 feet (25 yards, 6-8 lanes)
• Olympic pool: 164 feet (50 meters, 10 lanes) with 6'6" minimum depth

Pool safety regulations require depth markers at 3', 4', 5', 6', 8', and deeper. "NO DIVING" signs appear in areas less than 9 feet deep. These measurements help swimmers quickly assess safety.

Interior Design and Space Planning

Interior designers work in feet for furniture placement and room flow. Industry standards include:

• Seating area: 8' × 10' minimum for sofa, chairs, coffee table
• Dining area: Allow 3 feet per chair, 3-4 feet circulation around table
• Kitchen work triangle: 12-26 feet total (sum of distances between sink, stove, refrigerator)
• Island clearance: 3-4 feet on all sides for traffic flow
• TV viewing distance: 1.5-2.5× the diagonal screen size

A 12' × 18' living room (216 sq ft) allows space for a seating arrangement, TV console, and traffic flow. A 10' × 10' room (100 sq ft) feels cramped with more than a bed and dresser.

Window treatment specialists measure window width and height in feet and inches to calculate fabric requirements. Curtains typically extend 4-8 inches beyond window frame on each side, requiring precise foot-inch measurements.

Theater and Entertainment Venues

Stage dimensions, screen sizes, and venue layouts use feet:

• Proscenium width: 30-50 feet (typical theater)
• Stage depth: 20-40 feet
• Fly space: 60-80+ feet (above stage for scenery)
• Movie screen width: 40-90 feet (commercial theaters)
• IMAX screen: 72' × 52' (standard), 97' × 76' (largest)

Theatrical lighting positions specify trim height (distance from stage floor to light) in feet: 12', 18', 24'. Sound engineers place speakers based on feet of distance to achieve proper coverage—one speaker per 30-50 feet of venue length.

Venue capacity relates to square footage: 6-7 square feet per person for standing room, 10-12 sq ft per person for chair seating with aisles, 15-20 sq ft per person for banquet seating with tables.

Firefighting and Emergency Services

Fire departments specify equipment reach in feet: 75-foot aerial ladders, 100-foot platform trucks. Building codes restrict height based on fire equipment access—many jurisdictions limit wood-frame construction to 75 feet (roughly 7 stories) due to ladder reach limitations.

Hose lengths standardize at 50 feet or 100 feet. Firefighters calculate distance from hydrant to building entrance in feet to determine hose requirements. Water pressure calculations use feet of elevation: each foot of elevation change requires roughly 0.43 PSI pressure adjustment.

Emergency responders use feet for scene measurements: accident scenes, crime scenes, and disaster areas document positions and distances in feet. "Vehicle came to rest 150 feet beyond point of impact" provides clear spatial understanding.

Landscaping and Irrigation

Landscape contractors measure yards in feet for material calculations and cost estimates. Sod comes in rolls typically 2' × 5' (10 sq ft). Mulch, topsoil, and gravel calculate coverage in square feet at various depths: 1 cubic yard covers 324 sq ft at 1 inch depth, or 81 sq ft at 4 inches depth.

Irrigation system design uses feet for sprinkler spacing: 15-foot spacing for spray heads, 30-40 foot spacing for rotary heads. Drip irrigation calculates emitter placement in feet: 12-18 inches for flower beds, 2-3 feet for shrubs.

Tree planting requires spacing in feet based on mature spread: 15-20 feet apart for small trees, 30-40 feet for large shade trees, 50+ feet for massive specimens. "Plant trees 30 feet from building foundations" prevents root damage to structures.

Property grading specifies slope in inches per foot: 2-3 inches of drop per 10 feet of distance away from house foundations prevents water intrusion.

Common Conversion Mistakes to Avoid

Mistake 1: Adding Feet-Inches Without Converting to Common Units

The Error: Adding 5'9" + 3'8" = 8'17" instead of converting inches properly.

Why It Happens: People treat feet and inches as separate numbers and add them independently, forgetting that 12 inches equals 1 foot. The notation 8'17" appears mathematically correct but isn't valid because 17 exceeds 12 inches.

The Reality: You must convert excess inches to feet:

• 5'9" + 3'8" = 5' + 3' + 9" + 8" = 8' + 17"
• 17" = 12" + 5" = 1' + 5"
• Final answer: 8' + 1'5" = 9'5"

Alternatively, convert everything to inches: 5'9" = 69", 3'8" = 44", total = 113" = 9'5".

How to Avoid: Always convert total inches to feet when the inch value exceeds 12. Use a construction calculator that handles feet-inches math automatically, or convert entirely to inches, perform math, then convert back to feet-inches format.

Mistake 2: Confusing Square Feet with Linear Feet

The Error: Calculating that 100 feet of fencing encloses 100 square feet, or ordering 200 square feet of flooring for a 200-foot perimeter room.

Why It Happens: The terms sound similar, and people confuse perimeter (linear measurement) with area (square measurement).

The Reality:

• Linear feet measure distance in one dimension: 100 linear feet of fence is 100 feet long
• Square feet measure area in two dimensions: a 10' × 10' room = 100 square feet

A room with 200 feet of perimeter might be 50' × 50' (2,500 sq ft) or 40' × 60' (2,400 sq ft)—you cannot determine area from perimeter alone without knowing dimensions.

How to Avoid: Recognize that linear feet apply to one-dimensional items (fencing, crown molding, baseboards, rope), while square feet apply to two-dimensional surfaces (flooring, painting, roofing, sod). To find square footage, you must know both length and width dimensions.

Mistake 3: Incorrect Metric Conversions Using Rough Approximations

The Error: Converting 10 feet to meters as 3 meters, or 100 feet as 30 meters, using the approximation "divide by 3."

Why It Happens: People learn rough conversions like "a meter is about 3 feet" or "divide feet by 3 to get meters," which introduces 1.6% error.

The Reality: One foot equals exactly 0.3048 meters (not 0.30 or 0.33):

• 10 feet = 10 × 0.3048 = 3.048 meters (not 3.0 m or 3.33 m)
• 100 feet = 100 × 0.3048 = 30.48 meters (not 30 m or 33 m)
• 6 feet = 6 × 0.3048 = 1.829 meters (not 1.8 m or 2 m)

For reverse conversion, divide meters by 0.3048, or multiply by 3.28084:

• 10 meters = 10 ÷ 0.3048 = 32.81 feet (not 30 feet)

How to Avoid: Use the exact conversion factor 0.3048 when precision matters. For rough mental math, remember that 1 meter ≈ 3.28 feet (slightly more than 3 feet), so multiply meters by 3.3 for estimates. Always use precise calculations for construction, manufacturing, or engineering applications.

Mistake 4: Misunderstanding Aviation Altitude Context

The Error: Assuming a pilot saying "five hundred" means 500 feet altitude when they mean 500 feet above ground level, or confusion between AGL (Above Ground Level) and MSL (Mean Sea Level).

Why It Happens: Aviation uses multiple altitude references, and pilots abbreviate communications. "Five hundred" might mean 500 feet AGL during takeoff/landing, or flight level 5,000 (5,000 feet MSL) during cruise.

The Reality:

• AGL (Above Ground Level): Height above the terrain directly below the aircraft
• MSL (Mean Sea Level): Height above standard sea level reference
• Flight Level: Altitude in hundreds of feet MSL above 18,000 feet (FL350 = 35,000 ft MSL)

An airport at 5,000 feet elevation has a traffic pattern at 6,000 feet MSL (1,000 feet AGL). A pilot flying FL350 is at 35,000 feet MSL, which is 30,000 feet AGL if flying over that high-elevation airport.

How to Avoid: In aviation context, always clarify the reference: AGL for takeoff/landing/pattern work, MSL for en route altitudes, and flight levels above 18,000 feet. Pilots use altimeters that can be set to show either reference.

Mistake 5: Calculating Board Feet Incorrectly

The Error: Assuming a 2×4 board that's 8 feet long contains 8 board feet, or that a 1×6 board has 6 board feet per foot of length.

Why It Happens: People confuse linear feet (length) with board feet (volume measurement for lumber). Board feet calculations also require using nominal dimensions, not actual.

The Reality: One board foot = 1' × 1' × 1" (144 cubic inches of wood). Formula: (thickness" × width" × length') ÷ 12 = board feet.

Using nominal dimensions:

• 2×4 × 8' = (2 × 4 × 8) ÷ 12 = 5.33 board feet (not 8)
• 1×6 × 8' = (1 × 6 × 8) ÷ 12 = 4 board feet
• 2×6 × 10' = (2 × 6 × 10) ÷ 12 = 10 board feet

A 1×6 board contains 0.5 board feet per linear foot: (1 × 6 × 1) ÷ 12 = 0.5.

How to Avoid: Remember that board feet measure volume, not length. Always use nominal dimensions (2×4, not 1.5×3.5) in the calculation. Lumber yards price hardwood by board foot, so accurate calculation prevents overbuying or underestimating costs.

Mistake 6: Misreading Architectural Scales

The Error: Measuring a blueprint line as 3 inches and concluding the wall is 3 feet long, without checking the drawing scale.

Why It Happens: People measure blueprint dimensions with a ruler and forget to apply the scale factor, or misread the scale notation.

The Reality: Blueprints use scales like 1/4" = 1'0" (common residential) or 1/8" = 1'0" (larger buildings).

At 1/4" = 1'0" scale:

• 3" on drawing = 3 ÷ 0.25 = 12 feet actual dimension (not 3 feet)
• 0.5" on drawing = 0.5 ÷ 0.25 = 2 feet actual dimension

At 1/8" = 1'0" scale:

• 3" on drawing = 3 ÷ 0.125 = 24 feet actual dimension

How to Avoid: Always check the drawing scale before measuring anything. Use an architect's scale ruler marked with appropriate scales (1/4", 1/8", etc.) rather than a standard ruler. Better yet, read the dimension callouts printed on the drawing rather than measuring lines yourself.