Understanding Imperial and Metric Mass Units

Mass is measured using different systems around the world. While the metric system primarily uses kilograms and grams, the imperial system — still widely used in the United States and United Kingdom — uses pounds, ounces, stones, and tons.

Main Imperial Mass Units

• Ounce (oz) – A small unit of mass commonly used for food, postal packages, and jewelry. 1 ounce equals about 28.3495 grams.
• Pound (lb) – The standard unit for body weight and goods. 1 pound equals 0.453592 kilograms.
• Stone (st) – Mostly used in the UK and Ireland to measure body weight. 1 stone equals 14 pounds (about 6.35029 kilograms).
• Ton (short ton) – Used in the US, equals 2000 pounds (~907 kilograms).
• Ton (long ton) – Traditional UK ton, equals 2240 pounds (~1016 kilograms).
• Dram (dr) – A historic unit, primarily used in pharmacy, equals about 1.77185 grams.
• Grain (gr) – An ancient unit still used today for measuring bullets, arrows, and some precious materials; 1 grain equals about 64.79891 milligrams.

Fun Fact: Why Stones?

The "stone" as a unit has ancient origins and varied regionally for centuries. It was officially standardized in the UK in 1835 as 14 pounds per stone. Today, it remains popular in Britain and Ireland, especially for expressing human body weight. For example, someone might say, "I weigh 12 stone 3 pounds."

Mass Conversion Table