The pennyweight is a unit of mass primarily used to measure precious metals like gold and silver. It is equal in weight to 24 grains, 1/20th of a troy ounce, or 1.555 grams. Although it is uncommon in modern bullion trading, the pennyweight plays a critical role in the jewelry, dentistry, and scrap metal industries. Pennyweight is abbreviated as dwt, since the earliest common abbreviation for penny was ‘d’ for denarius, which is not to be confused with DWT, or dead weight tonnage, a unit used for ships.
Historical Context of the Pennyweight
The pennyweight was a vital part of medieval trade and commerce, particularly for transactions involving precious metals, in which the pennyweight helped standardize trade across regions. This was essential for building trust between merchants, ensuring that goods like silver and gold could be traded with a common understanding of value.
Markets and fairs thrived in medieval Europe, thanks in part to consistent measures like the pennyweight. The reliability of these measurements allowed for smoother transactions and contributed to the growth of international trade.
Origins of the Pennyweight
The term pennyweight is rooted in medieval England, where it referred to the weight of one silver penny, a medieval coin. King Offa of Mercia introduced pennies in the late 8th century, which were used across various English kingdoms. Early pennies weighed 1/240th of a Saxon pound of silver (about 1.46 grams) and established the penny as both a monetary and weight unit.
By the Middle Ages, the pennyweight unit had become a more formalized measure defined as 1/20th of an ounce and 1/240th of a pound of sterling silver. This standardization was paramount for trade, allowing merchants to exchange goods with confidence in values based on precious metal content.
From the Tower System to the Troy System
In 1527, England transitioned from the Tower to the troy weight system, which is still in use. The troy system defines the pennyweight as 24 troy grains or 1.555 grams. Adopting the troy system aligned England with international trade standards, facilitating transactions throughout Europe. The troy weight system, originating in the Roman era and named after the French city of Troyes, became widely adopted for precious metals due to its precision. This system remains a cornerstone of the precious metals industry.
Other Weight Units in Medieval England
The medieval English weight system utilized different measures for different purposes. These included:
- Pound (lb): The basic unit of weight, with variations such as the Tower pound and the troy pound. The Tower was equal to 5,400 grains, while the troy pound weighed 5,760 grains.
- Ounce (oz): The troy ounce weighed 20 pennyweights or 480 grains.
- Grain (gr): The grain was the smallest unit of weight in all systems. One grain was the same across different systems and was based on the weight of a single grain of barley.
- Stone (st): The stone was utilized for larger quantities, particularly in trade. One stone was equal to about 14 pounds.
- Hundredweight (cwt): Hundredweights were used for even larger quantities, particularly in agriculture. There were two types: the short hundredweight (100 pounds) and the long hundredweight (112 pounds).
- Ton: The largest unit, used for very large quantities. The short ton was 2,000 pounds, and the long ton was 2,240 pounds.
These units eventually influenced the development of the Imperial and U.S. customary systems.
Modern Usage of the Pennyweight
While the pennyweight is no longer used in everyday trade, it remains crucial in industries that handle precious metals:
- Jewelry: Many jewelers use pennyweights to calculate the weight of precious metals required for crafting or repairing jewelry. This is helpful for determining the precise cost of metals like gold, silver, or platinum in each piece.
- Dentistry: Dental labs use pennyweights to measure the amount of precious metals in dental restorations, which include crowns and inlays.
- Metal Valuation: Pennyweights are often used in the scrap metal industry, where the value of metals is calculated based on their weight. Metals are typically weighed in pennyweights before their value is assessed and converted into market prices.
Using Pennyweights for Precious Metals Today
The use of pennyweights in the precious metals industry is tied to the need for precise measurements. Since metals like gold and silver are valued by their weight, some jewelers and metal buyers prefer the pennyweight because it simplifies calculations when working with the troy system. For example, when crafting a gold ring, a jeweler can quickly determine how much gold is required by measuring it in pennyweights and then calculating the total cost based on the current price per pennyweight.
Converting Pennyweight to Grams and Troy Ounces
Use this table to convert pennyweights to grams and troy ounces.
| Unit | dwt | Grams |
| 1 Pennyweight | 1 dwt | 1.555 |
| 1 Troy Ounce | 20 dwt | 31.1 |
| 1 Troy Pound | 240 | 373.242 |
| 1 Kilogram | 643.015 dwt | 1000 |
How to Find the Value of Gold by Pennyweight
The APMEX Gold Price page has a Gold Calculator that offers a convenient way to determine the value of your gold in pennyweights, grains, grams, and more. By entering the weight in any of these units, you can quickly see how much your precious metals are worth, streamlining the valuation process whether you are insuring or selling.
