WeightConverter
Instantly convert weight units including Milligram, Gram, and more.
About Weight Units
Mass is the measure of the amount of matter in an object, while weight is the gravitational force acting on that mass. In everyday usage these terms are interchanged freely, but in physics they are distinct: a 70 kg astronaut has the same mass on the Moon as on Earth, but only about one-sixth the weight. The SI base unit is the kilogram (kg), redefined in 2019 in terms of fundamental physical constants. The US customary and imperial systems use ounces (oz) and pounds (lb) for moderate masses and short or long tons for heavy loads.
The history of weighing units reflects centuries of trade and commerce. The avoirdupois system — used for everyday goods — takes its name from Anglo-French 'aveir de pois' (goods of weight) and was formalized in 14th-century England. The troy system, still used for precious metals and gems, traces to the Champagne fairs of Troyes, France, where merchants from across Europe settled accounts. The metric system introduced the gram and kilogram in 1795 as units grounded in a physical constant: 1 gram was originally the mass of 1 cm³ of water at 4 °C. Today, the kilogram is defined by fixing the Planck constant.
Understanding mass and weight units matters in a remarkable variety of contexts. Kitchen recipes switch between grams and ounces depending on the author's country. Physicians prescribe medication in milligrams and monitor patient weight in kilograms or stones-and-pounds. Logistics companies calculate shipping costs by kilogram or pound. Metals traders price gold in troy ounces. The three different 'tons' — US short ton (907 kg), UK long ton (1,016 kg), and metric tonne (1,000 kg) — can cause costly errors in international contracts if not specified clearly.
Common Weight Conversions
| From | To |
|---|---|
| 1 pound (lb) | 453.592 g |
| 1 kilogram | 2.20462 lbs |
| 1 ounce (oz) | 28.3495 g |
| 1 stone | 6.35029 kg (14 lbs) |
| 1 metric tonne | 1,000 kg = 2,204.62 lbs |
| 1 US short ton | 907.185 kg |
| 1 gram | 0.035274 oz |
| 1 troy ounce | 31.1035 g |
| 1 kg | 1,000 g = 1,000,000 mg |
| 100 lbs | 45.3592 kg |
| 1 milligram | 0.001 g = 0.000001 kg |
| 1 UK long ton | 1,016.05 kg = 2,240 lbs |
| 1 pound | 16 ounces |
| 1 stone | 14 pounds = 6.35029 kg |
| 1 metric ton | 1.10231 US short tons |
Frequently Asked Questions
One kilogram equals approximately 2.20462 pounds. For a quick mental estimate, multiply kilograms by 2.2.
One avoirdupois ounce equals 28.3495 grams. A troy ounce (used for precious metals) is heavier at 31.1035 grams.
Mass measures the amount of matter in an object (constant everywhere); weight is the gravitational force on that mass and varies by location. On the Moon, your mass stays the same but your weight is about 1/6 of Earth's.
Exactly 1,000 kilograms make one metric ton (tonne).
A troy ounce (used for gold, silver, and gemstones) equals 31.1035 grams. A standard (avoirdupois) ounce equals only 28.3495 grams. When you see gold prices quoted 'per ounce,' that is always the troy ounce.
There are exactly 16 avoirdupois ounces in one pound. This is the system used for food, shipping, and everyday goods. The troy pound (used historically for precious metals) contains 12 troy ounces, but the troy pound is now rarely used.
There are exactly 1,000 grams in one kilogram. The prefix 'kilo-' means 1,000 in the SI system.
The US short ton = 2,000 lbs (907.185 kg). The UK long ton = 2,240 lbs (1,016.05 kg). The metric tonne = 1,000 kg (2,204.62 lbs). In international contracts, always specify which ton is intended to avoid costly confusion.