Acre (acre) - Unit Information & Conversion

Quick Answer

What is an Acre? An acre is a unit of land area equal to 43,560 square feet.

Quick Visual:

• 1 acre ≈ 90% of an American football field (including end zones).
• 1 acre ≈ 16 tennis courts.
• 1 acre ≈ A square 208.7 feet on each side.

Common Conversions:

• 1 acre = 43,560 sq ft
• 1 acre = 4,840 sq yd
• 1 acre = 0.4047 hectares
• 1 square mile = 640 acres

Quick Comparison Table

Acres	Square Feet	Square Meters	Hectares	Common Example
0.25 ac	10,890 sq ft	1,012 m²	0.10 ha	Large suburban lot
0.5 ac	21,780 sq ft	2,023 m²	0.20 ha	Estate home lot
1 ac	43,560 sq ft	4,047 m²	0.40 ha	Small farm plot
5 ac	217,800 sq ft	20,234 m²	2.02 ha	Hobby farm
10 ac	435,600 sq ft	40,469 m²	4.05 ha	Small ranch
40 ac	1,742,400 sq ft	161,874 m²	16.19 ha	Quarter section (homestead)
160 ac	6,969,600 sq ft	647,497 m²	64.75 ha	Full homestead section
640 ac	27,878,400 sq ft	2,589,988 m²	259.00 ha	1 square mile

Definition

The Mathematical Definition

1 Acre = 43,560 square feet

This definition comes from the traditional measurement:

• 1 chain = 66 feet (Gunter's chain)
• 1 furlong = 660 feet (10 chains)
• 1 acre = 1 chain × 1 furlong = 66 ft × 660 ft = 43,560 sq ft

In Other Units:

• Square Yards: $\frac{43,560}{9} = 4,840 \text{ sq yd}$
• Square Meters: $43,560 \times 0.09290304 = 4,046.856 \text{ m}^2$
• Hectares: $\frac{4,046.856}{10,000} = 0.4047 \text{ ha}$

Shape Doesn't Matter

An acre can be any shape as long as the total area is 43,560 sq ft.

• Square Acre: 208.71 ft × 208.71 ft
• Rectangular Acre: 66 ft × 660 ft (traditional furlong × chain)
• Circular Acre: Radius of 117.75 ft
• Irregular Acre: Any polygon with 43,560 sq ft area

The "Chain" System

The acre is part of an elegant measurement system based on Gunter's chain:

• 1 link = 7.92 inches (0.66 ft)
• 1 chain = 100 links = 66 ft
• 1 furlong = 10 chains = 660 ft = 1/8 mile
• 1 mile = 8 furlongs = 80 chains = 5,280 ft
• 1 acre = 10 square chains

This system made surveying incredibly efficient. A surveyor could measure land using a physical chain and easily calculate acreage.

History: From Oxen to GPS

Ancient Origins

The concept of measuring land by how much could be worked in a day is ancient and universal:

• Roman Jugerum: The area two oxen could plow in one day (~2/3 acre).
• German Morgen: "Morning's work" of plowing (~0.6-0.9 acres).
• French Arpent: Regional French unit (~0.85 acres).
• English Acre: The amount one man with one ox could plow in one day.

The problem? Soil quality varied. Rocky, hilly land took longer to plow than flat, fertile land. This led to regional variations in the "acre."

Medieval Chaos

In medieval England, there were dozens of different "acres":

• Statute Acre: 43,560 sq ft (the modern standard).
• Irish Acre: 7,840 sq yd (1.62 statute acres).
• Scottish Acre: 6,150 sq yd (1.27 statute acres).
• Cheshire Acre: 10,240 sq yd (2.11 statute acres).
• Cornish Acre: Varied by location.

Land disputes were common because nobody could agree on the size of an acre!

The Gunter Revolution (1620)

Edmund Gunter, an English clergyman and mathematician, invented the surveyor's chain in 1620. This 66-foot chain (divided into 100 links) became the standard tool for land measurement.

Why 66 feet?

• 1 chain = 4 rods (or poles) = 66 feet.
• 10 chains = 1 furlong = 660 feet = 1/8 mile.
• 80 chains = 1 mile = 5,280 feet.

This made calculations trivial:

• 1 acre = 10 square chains.
• 640 acres = 1 square mile.

The Homestead Act (1862)

In the United States, the Homestead Act of 1862 granted 160 acres of public land to settlers who would farm it for 5 years. This "quarter section" (1/4 of a square mile) became the iconic American farm size.

The Grid System:

• 1 section = 1 square mile = 640 acres.
• 1 quarter section = 160 acres (homestead).
• 1 township = 36 sections = 23,040 acres = 36 square miles.

This grid system is why much of the American Midwest has perfectly straight roads running north-south and east-west.

Modern Standardization

• 1878: Weights and Measures Act (UK) formalized the "statutory acre."
• 1959: International yard and pound agreement standardized the acre globally.
• Today: The acre is legally defined as exactly 4,046.8564224 square meters.

Real-World Examples

Residential Property Sizes

Property Type	Typical Size	Description
Urban Lot	0.1-0.25 ac	4,356-10,890 sq ft. Typical city house lot.
Suburban Lot	0.25-0.5 ac	10,890-21,780 sq ft. Standard suburban home.
Large Suburban	0.5-1 ac	21,780-43,560 sq ft. Estate home with yard.
Rural Residential	1-5 ac	Small acreage for privacy, gardens, animals.
Hobby Farm	5-20 ac	Enough for horses, small crops, or livestock.
Small Farm	20-100 ac	Commercial farming (vegetables, orchards).
Medium Farm	100-500 ac	Grain farming, cattle ranching.
Large Farm	500-2,000+ ac	Industrial agriculture.

Famous Land Areas (in Acres)

• Central Park (NYC): 843 acres.
• Disneyland (California): 85 acres (park only), 510 acres (entire resort).
• Vatican City: 109 acres (0.17 square miles).
• Monaco: 499 acres (0.78 square miles).
• The Pentagon: 29 acres (building footprint), 583 acres (entire complex).
• Mall of America: 67 acres (under roof).
• King Ranch (Texas): 825,000 acres (1,289 square miles) - larger than Rhode Island!

Visual Comparisons

1 Acre is approximately:

• 90.75% of an American football field (including end zones).
• 75% of a soccer field (FIFA regulation).
• 16 tennis courts (singles).
• 9 basketball courts (NBA regulation).
• 2.5 Olympic swimming pools (by surface area).
• 156 parking spaces (standard 9×18 ft stalls).

Common City Blocks:

• Manhattan Block: ~2-5 acres (varies greatly).
• Chicago Block: ~3 acres (typical).
• Portland Block: ~2 acres (200 ft × 200 ft).

Common Uses

1. Real Estate

The acre is the standard unit for land sales in the US, UK, Canada, and Australia.

Residential:

• Lot sizes for homes, especially in suburban and rural areas.
• Zoning regulations often specify minimum lot sizes in acres (e.g., "R-1 zoning: 1-acre minimum").

Commercial:

• Shopping centers, office parks, industrial sites.
• "10-acre commercial development site available."

Undeveloped Land:

• Timberland, hunting land, investment property.
• "40-acre wooded parcel with creek frontage."

2. Agriculture

Farmers use acres to:

• Measure field sizes: "I have 80 acres in corn this year."
• Calculate yields: "We harvested 180 bushels per acre."
• Apply inputs: "Apply 150 lbs of nitrogen per acre."
• Comply with regulations: "You must leave 10 acres fallow for conservation."

Crop Yields (US Average):

• Corn: 177 bushels/acre.
• Soybeans: 52 bushels/acre.
• Wheat: 47 bushels/acre.
• Cotton: 900 lbs/acre.

3. Forestry

Timber is sold by the acre.

• Managed Forest: "200 acres of pine plantation."
• Timber Yield: "This stand will produce 20 cords per acre."

4. Land Management & Conservation

• National Parks: Measured in acres (Yellowstone: 2.2 million acres).
• Wetlands: "Restore 500 acres of wetlands."
• Wildlife Habitat: "Preserve 1,000 acres for endangered species."

5. Sports & Recreation

• Golf Courses: 100-200 acres (18 holes).
• Ski Resorts: "1,500 acres of skiable terrain."
• Hunting Leases: "Lease 500 acres for deer hunting."

Conversion Guide

Acres to Square Feet

The most common conversion for property buyers.

Formula: $$ \text{Square Feet} = \text{Acres} \times 43,560 $$

Acres	Square Feet
0.25	10,890
0.5	21,780
1	43,560
2	87,120
5	217,800
10	435,600

Acres to Hectares

For international comparisons.

Formula: $$ \text{Hectares} = \text{Acres} \times 0.4047 $$

Acres	Hectares
1	0.40
5	2.02
10	4.05
100	40.47
640 (1 sq mi)	259.00

Square Miles to Acres

For large land parcels.

Formula: $$ \text{Acres} = \text{Square Miles} \times 640 $$

Square Miles	Acres
0.5	320
1	640
10	6,400
100	64,000