Pennyweight (dwt) - Unit Information & Conversion

Quick Answer

1 pennyweight (dwt) = 1.55517384 grams = 24 grains = 1/20 troy ounce

A pennyweight represents the traditional weight of a medieval silver penny and remains the practical working unit for jewelers and precious metal dealers worldwide.

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Quick Comparison Table

Weight Unit	Equals 1 Pennyweight
Grains	24 gr
Grams	1.55517384 g
Troy Ounces	0.05 oz t (1/20)
Troy Pounds	0.00416667 lb t (1/240)
Ounces (avoirdupois)	0.0548571 oz
Carats (metric)	7.7758692 ct

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Definition

What Is a Pennyweight?

The pennyweight (symbol: dwt) is a unit of mass within the troy weight system, equal to exactly 1.55517384 grams or 1/20th of a troy ounce. It consists of precisely 24 grains, making it a convenient intermediate unit for measuring precious metals and gemstones.

Troy vs. Avoirdupois Systems

The pennyweight belongs to the troy weight system, which differs fundamentally from the avoirdupois system used for most everyday weights:

• Troy system: 12 ounces = 1 pound (used for precious metals, gemstones)
• Avoirdupois system: 16 ounces = 1 pound (used for general commerce)
• Key difference: A troy ounce (31.1035 g) is heavier than an avoirdupois ounce (28.3495 g), but a troy pound (373.24 g) is lighter than an avoirdupois pound (453.59 g)

Official Definition

Since the 1959 international yard and pound agreement, the pennyweight is defined as:

1 dwt = 24 grains = 0.05 troy ounces = 1.55517384 grams (exact)

This definition is recognized by the United States, United Kingdom, Canada, Australia, New Zealand, and South Africa, ensuring consistency in precious metals trading worldwide.

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History

Ancient Origins: The Silver Penny

The pennyweight's history traces to Anglo-Saxon England, where silver pennies served as both currency and weight standards. During the reign of King Offa of Mercia (757-796 AD), silver pennies were standardized at one pennyweight each, creating a direct relationship between monetary value and precious metal weight.

This system meant that:

• 1 silver penny = 1 pennyweight of silver
• 20 pennies = 1 shilling = 1 troy ounce of silver
• 240 pennies = 1 pound sterling = 1 troy pound of silver

This elegant correspondence between money and weight lasted nearly 1,200 years in principle, though the silver content of coins gradually decreased over centuries.

Medieval Standardization (1266-1327)

The Composition of Yards and Perches statute of 1266 under King Henry III formally standardized English weights and measures, including the pennyweight at 24 grains. This was reinforced by the Tractatus de Ponderibus et Mensuris (Treatise on Weights and Measures) issued during the reign of Edward I (1303-1307).

The Worshipful Company of Goldsmiths, granted its royal charter in 1327, became the official regulatory body for precious metals in England. The company enforced pennyweight standards through its hallmarking system, which required all gold and silver items to be assayed (tested for purity) and stamped with official marks. Goldsmiths' Hall in London became the center of this regulatory system—hence the term "hallmark."

Troyes Connection

The term "troy weight" derives from Troyes, France, a major medieval trading city hosting international fairs where merchants from across Europe gathered. By the 12th-13th centuries, Troyes had developed standardized weight systems for precious metals that were adopted by merchants throughout Europe.

English goldsmiths adopted the Troyes system because it was already used by continental traders, ensuring consistency in international precious metals commerce. The system's subdivision structure (1 pound = 12 ounces, 1 ounce = 20 pennyweights, 1 pennyweight = 24 grains) reflected medieval base-12 and base-20 counting preferences.

British Imperial Codification (1824-1878)

The British Weights and Measures Act of 1824 consolidated various troy weight standards used across Britain, officially defining the troy pound as 5,760 grains and the pennyweight as 1/240th of a troy pound (24 grains).

The Weights and Measures Act of 1878 refined these definitions and legally mandated troy weights for precious metals transactions throughout the British Empire. This act specified that gold, silver, platinum, and precious stones must be weighed using troy units, with the pennyweight serving as the practical working unit for jewelers and dealers.

American Adoption

The United States adopted the British troy system for precious metals following independence. The U.S. Coinage Act of 1792 established the dollar based on a specific weight of silver (371.25 grains = 15.4375 pennyweights), directly linking American currency to pennyweight standards.

The National Bureau of Standards (now NIST) formalized the pennyweight in U.S. regulations, and it remains a legally recognized unit for precious metals commerce under U.S. law today.

International Agreement (1959)

The 1959 international yard and pound agreement among English-speaking nations established exact metric equivalents for imperial units, defining the grain (and therefore the pennyweight) in terms of the kilogram:

• 1 grain = exactly 64.79891 milligrams
• 1 pennyweight = 24 grains = exactly 1.55517384 grams

This agreement ended minor variations in troy weight definitions across different countries and established the standard used worldwide today.

Modern Persistence

Despite metrication efforts in the United Kingdom (1965-present), Australia (1970s), and other Commonwealth nations, the pennyweight persists in the precious metals and jewelry industries. The unit's survival reflects:

1. International trade standards: Precious metals are traded globally in troy ounces and pennyweights
2. Industry infrastructure: Scales, reference books, and pricing systems are built around troy units
3. Practical convenience: Pennyweights provide appropriate precision for jewelry work
4. Legal requirements: Many jurisdictions still mandate troy weights for bullion hallmarking

The London Bullion Market Association (LBMA), established 1987, continues to use troy ounces (and by extension, pennyweights) as the global standard for precious metals trading, ensuring the unit's continued relevance.

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Real-World Examples

Tiny Jewelry (1-2 dwt)

Small gold earrings, delicate pendants, gemstone settings:

• Simple gold stud earrings: 0.8-1.5 dwt
• Small gold pendant: 1.5-2.5 dwt
• Single gemstone setting: 0.5-1.0 dwt
• Engagement ring setting (without stone): 1.8-3.0 dwt

Typical Jewelry (3-8 dwt)

Wedding rings, standard necklaces, bracelets:

• Men's gold wedding band: 4-8 dwt
• Women's gold wedding band: 3-5 dwt
• Gold chain necklace (18 inches): 5-12 dwt
• Gold bracelet: 6-15 dwt
• Silver necklace: 8-20 dwt

Substantial Jewelry (10-30 dwt)

Statement pieces, heavy chains, class rings:

• College class ring: 12-20 dwt
• Heavy gold chain: 15-35 dwt
• Large pendant with setting: 8-15 dwt
• Men's gold ring with large stone: 10-18 dwt
• Substantial silver bracelet: 20-40 dwt

Coins and Bullion (15-50 dwt)

Precious metal coins and small bars:

• American Silver Eagle (1 oz): 20 dwt
• American Gold Eagle (1 oz): 20 dwt
• Canadian Maple Leaf (1 oz): 20 dwt
• Pre-1965 U.S. silver quarter: ~3.75 dwt (silver content)
• Pre-1965 U.S. silver dollar: ~15 dwt (silver content)
• 1 oz gold bar: 20 dwt
• 10 gram gold bar: ~6.43 dwt

Large Items (50+ dwt)

Heavy jewelry, ceremonial objects, larger bullion:

• Heavy gold necklace with large pendant: 50-100 dwt
• Gold trophy or award: 80-200 dwt
• Ceremonial gold chain of office: 150-300 dwt
• 5 oz gold bar: 100 dwt
• Silver tea service piece: 200-600 dwt

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Common Uses

1. Jewelry Manufacturing and Valuation

Jewelers use pennyweights as their primary working unit for several reasons:

Precision without unwieldiness: A pennyweight provides finer precision than troy ounces (1/20th oz increments) without requiring the tiny fractions that grain measurements would demand. A jeweler can easily work with "5.5 dwt of gold" rather than "110 grains" or "0.275 troy ounces."

Pricing calculations: Precious metal dealers quote prices per pennyweight for smaller quantities. For example, if gold is $2,000/troy ounce, it's $100/dwt ($2,000 ÷ 20). This makes quick calculations easier: a 6 dwt ring contains $600 worth of gold.

Material estimation: When designing custom jewelry, goldsmiths estimate required material in pennyweights: "This ring design will need approximately 8 pennyweights of 14-karat gold, plus 2 pennyweights for the setting."

Scrap valuation: When buying or selling scrap gold/silver, dealers weigh items in pennyweights to calculate melt value: "Your broken gold chain weighs 12.3 pennyweights at 14-karat purity, which contains 7.175 dwt of pure gold."

Industry standard scales: Professional jewelers' scales typically display troy ounces subdivided into 20 pennyweights, with precision to 0.01 dwt (0.24 grains).

2. Precious Metals Trading and Refining

Refinery lot tracking: When refineries process precious metals, they track batches in troy ounces and pennyweights: "Batch #4782: 347 oz 15 dwt of sterling silver scrap."

Assay reporting: Assay offices (testing precious metal purity) report results in pennyweights: "Sample contained 18.65 dwt of pure gold and 1.35 dwt of copper alloy."

Bullion fractional trading: Small precious metals dealers use pennyweights for transactions smaller than full troy ounces: "We buy silver at $1.20/dwt" ($24/oz).

Hallmarking records: Official hallmarking offices record item weights in pennyweights when stamping fineness marks: "Ring assayed and hallmarked: 5.2 dwt, 18kt gold."

3. Gemstone Settings and Diamond Work

While gemstones themselves are weighed in carats (1 carat = 200 mg), the metal settings are measured in pennyweights:

Prong settings: "Four-prong platinum setting for 1-carat diamond: 1.8 dwt" Bezels: "18kt gold bezel for round cabochon: 2.3 dwt" Channel settings: "Platinum channel for seven 0.25ct diamonds: 4.5 dwt"

Conversion reference: 1 pennyweight = 7.776 metric carats (though carats aren't used for metal)

4. Coin Collecting (Numismatics)

Coin collectors reference pennyweights to verify authenticity and silver/gold content:

Historical silver coins: Pre-1965 U.S. dimes, quarters, and half-dollars contain 90% silver. Their pennyweight ratings help collectors calculate precious metal value:

• 1964 Kennedy half-dollar: 7.234 dwt silver content
• 1964 Washington quarter: 3.617 dwt silver content
• 1964 Roosevelt dime: 1.447 dwt silver content

Gold coins: American Gold Eagles, Krugerrands, and other bullion coins are often referenced in pennyweights for smaller transactions:

• 1/10 oz Gold Eagle: 2 dwt
• 1/4 oz Gold Eagle: 5 dwt
• 1/2 oz Gold Eagle: 10 dwt

Counterfeit detection: Knowing the correct pennyweight of historic coins helps detect counterfeits: "This coin claims to be an 1893 Morgan silver dollar but weighs only 14.2 dwt instead of the correct 16.716 dwt—likely counterfeit."

5. Dental Alloys and Dentistry

Dental laboratories use pennyweights for precious metal dental alloys:

Gold crowns and bridges: Dental gold alloys (typically gold-palladium-silver combinations) are purchased and tracked in pennyweights: "Order 50 dwt of type III gold casting alloy for crown fabrication."

Scrap recovery: Dental offices collect scrap gold from old crowns, bridges, and orthodontic appliances, selling it by pennyweight to refiners: "Monthly dental scrap recovery: 18.5 dwt mixed gold alloys."

Material costs: Dental labs calculate restoration costs based on pennyweight requirements: "Three-unit bridge requires approximately 8 pennyweights of high-noble alloy, current cost $95/dwt = $760 materials."

6. Watchmaking and Repair

Watch repairmen and manufacturers use pennyweights for precious metal watch cases and components:

Gold watch cases: "18kt gold pocket watch case: 42 dwt" Solid gold bracelet links: "Replacement gold bracelet links: 1.2 dwt each" Vintage watch restoration: "Restore gold crown and stem: requires 0.8 dwt 14kt gold stock"

7. Hallmarking and Legal Compliance

Official assay offices and hallmarking authorities use pennyweights in legal documentation:

Fineness certification: British Hallmarking Act requires items over certain pennyweight thresholds be hallmarked:

• Gold: items over 0.5 dwt must be hallmarked
• Silver: items over 5 dwt must be hallmarked
• Platinum: items over 0.33 dwt must be hallmarked

Export documentation: Precious metals crossing international borders require customs declarations listing pennyweight and fineness: "Shipment: 1,450 dwt of 999 fine gold bullion."

Consumer protection: Trading standards enforce accurate weight declarations, with penalties for misrepresenting pennyweight on jewelry labels.

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Conversion Guide

Converting Pennyweights to Common Units

To Grams

Formula: dwt × 1.55517384 = grams

Examples:

• 5 dwt = 5 × 1.55517384 = 7.7759 g
• 12.5 dwt = 12.5 × 1.55517384 = 19.4397 g
• 100 dwt = 100 × 1.55517384 = 155.517 g

Quick approximation: 1 dwt ≈ 1.56 g

To Troy Ounces

Formula: dwt ÷ 20 = troy ounces

Examples:

• 20 dwt = 20 ÷ 20 = 1 oz t
• 10 dwt = 10 ÷ 20 = 0.5 oz t
• 35 dwt = 35 ÷ 20 = 1.75 oz t

Quick mental math: Divide by 20 or multiply by 0.05

To Grains

Formula: dwt × 24 = grains

Examples:

• 1 dwt = 1 × 24 = 24 gr
• 5 dwt = 5 × 24 = 120 gr
• 0.5 dwt = 0.5 × 24 = 12 gr

Quick mental math: Multiply by 24

To Metric Carats

Formula: dwt × 7.7758692 = carats

Examples:

• 1 dwt = 1 × 7.7758692 = 7.776 ct
• 5 dwt = 5 × 7.7758692 = 38.879 ct

Note: This is theoretical—carats are used for gemstones, not metal

Converting Common Units to Pennyweights

From Grams

Formula: grams ÷ 1.55517384 = dwt

Examples:

• 10 g = 10 ÷ 1.55517384 = 6.43 dwt
• 31.1035 g (1 oz t) = 31.1035 ÷ 1.55517384 = 20 dwt
• 50 g = 50 ÷ 1.55517384 = 32.15 dwt

Quick approximation: Multiply grams by 0.643 (dwt ≈ g × 0.643)

From Troy Ounces

Formula: troy ounces × 20 = dwt

Examples:

• 1 oz t = 1 × 20 = 20 dwt
• 0.5 oz t = 0.5 × 20 = 10 dwt
• 2.75 oz t = 2.75 × 20 = 55 dwt

Quick mental math: Multiply by 20

From Grains

Formula: grains ÷ 24 = dwt

Examples:

• 24 gr = 24 ÷ 24 = 1 dwt
• 120 gr = 120 ÷ 24 = 5 dwt
• 480 gr = 480 ÷ 24 = 20 dwt (1 oz t)

Quick mental math: Divide by 24

Practical Jewelry Calculations

Gold Value Calculation

If gold is $2,100 per troy ounce:

• Price per pennyweight = $2,100 ÷ 20 = $105/dwt
• 6.5 dwt gold ring = 6.5 × $105 = $682.50 (melt value for pure gold)
• For 14kt gold (58.3% pure): $682.50 × 0.583 = $397.90 actual gold value

Material Requirement Estimation

Custom ring design requires 7 dwt of 18kt gold:

• Pure gold needed: 7 dwt × 0.75 (18kt = 75% pure) = 5.25 dwt pure gold
• In grams: 7 dwt × 1.555 = 10.89 g total alloy
• In troy ounces: 7 ÷ 20 = 0.35 oz t

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Common Conversion Mistakes

1. Confusing Troy Ounces with Avoirdupois Ounces

The Mistake: Using the wrong ounce conversion factor

Why It Happens: People assume all ounces are the same (28.35 g)

The Truth:

• Avoirdupois ounce (regular ounce): 28.3495 g
• Troy ounce (precious metals): 31.1035 g
• Difference: Troy ounce is 9.7% heavier

Impact: Converting 20 dwt using avoirdupois ounce gives 31.10 g (wrong) instead of 31.10 g (correct but different reasoning)

Correct approach: Always use troy ounces (20 dwt = 1 oz t = 31.1035 g)

2. Mixing Carat (Purity) with Carat (Weight)

The Mistake: Confusing karat (gold purity) with carat (gemstone weight)

Why It Happens: Similar spelling but completely different meanings

The Truth:

• Karat (kt or K): Gold purity out of 24 (e.g., 18kt = 18/24 = 75% pure gold)
• Carat (ct): Gemstone weight (1 ct = 200 mg = 0.1286 dwt)
• Different units: Never confused by professionals, frequently confused by consumers

Impact: A "14-carat gold ring" doesn't mean the gemstone weighs 14 carats; it means the gold is 14/24 pure (58.3%)

Correct approach: Use "karat" (or kt) for gold purity, "carat" (ct) for gemstone weight

3. Forgetting to Account for Alloy Purity

The Mistake: Calculating gold value using total pennyweight without adjusting for purity

Why It Happens: Assuming jewelry weight equals pure gold weight

The Truth: Most jewelry is alloyed:

• 24kt gold: 99.9% pure (essentially pure gold)
• 22kt gold: 91.7% pure (common in Asia/Middle East)
• 18kt gold: 75% pure (European standard)
• 14kt gold: 58.3% pure (American standard)
• 10kt gold: 41.7% pure (minimum legal "gold" in USA)

Impact: A 10 dwt 14kt gold ring contains only 5.83 dwt of pure gold

Calculation:

• Total weight: 10 dwt
• Purity: 14kt ÷ 24 = 0.583 (58.3%)
• Pure gold: 10 dwt × 0.583 = 5.83 dwt pure gold

4. Rounding Errors in Conversion Factors

The Mistake: Using imprecise conversion factors for official valuations

Why It Happens: Using "1 dwt ≈ 1.56 g" instead of exact value

The Truth: Official definition is 1 dwt = 1.55517384 g (exact)

Impact on large quantities:

• 1,000 dwt using approximation: 1,000 × 1.56 = 1,560 g
• 1,000 dwt exact: 1,000 × 1.55517384 = 1,555.17 g
• Error: 4.83 g difference (~$300 at $2,000/oz gold prices)

Correct approach: Use exact factors for any significant transaction

5. Confusing Pennyweight with Penny Sterling (Pence)

The Mistake: Thinking pennyweight relates to modern British pence

Why It Happens: The word "penny" appears in both

The Truth:

• Pennyweight (dwt): Weight unit = 1.555 g
• Penny/Pence (p): Modern British currency = 1/100 pound sterling
• Historical connection: Medieval silver pennies weighed one pennyweight, but this connection ended with decimalization in 1971

Impact: No calculation confusion, but conceptual misunderstanding

Correct understanding: The pennyweight is a weight unit only; modern pence are pure currency with no weight relationship

6. Incorrect Troy Pound Calculations

The Mistake: Assuming 1 troy pound = 16 troy ounces (like avoirdupois)

Why It Happens: Muscle memory from regular pounds (16 oz = 1 lb)

The Truth:

• Troy pound: 12 troy ounces = 240 pennyweights = 5,760 grains
• Avoirdupois pound: 16 ounces = 7,000 grains
• Difference: Troy pound is actually lighter (373.24 g vs 453.59 g)

Impact: 240 dwt ≠ 16 oz t; 240 dwt = 12 oz t (1 troy pound)

Correct approach: Remember troy system uses 12-based divisions (12 oz/lb, 20 dwt/oz)

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