Weight and mass units appear in body weight, shipping, cooking, science, medicine, fitness, manufacturing, and trade. In everyday language, people often say weight when they mean mass. In technical work, the distinction matters: mass measures the amount of matter, while weight is a force caused by gravity.
Mass vs weight
Mass describes how much matter an object contains. Weight is the gravitational force on that mass. Everyday scales report values in kilograms, pounds, grams, or ounces, so consumer-facing pages often use the familiar phrase weight conversion. Scientific formulas usually require careful attention to mass, force, and gravity.
Metric mass units
Metric mass units are decimal and based around the kilogram, which is the SI base unit for mass. Grams, milligrams, and metric tons are related to the kilogram by powers of ten.
| Unit | Symbol | Relationship to kilogram | Typical use |
|---|---|---|---|
| milligram | mg | 0.000001 kg | medicine, supplements, chemistry |
| gram | g | 0.001 kg | food, recipes, small objects, science |
| kilogram | kg | 1 kg | body weight, shipping, commerce, SI mass |
| metric ton | t | 1,000 kg | freight, industry, agriculture, bulk materials |
Customary weight units
US customary and imperial contexts commonly use pounds, ounces, stones, and tons. The pound is the main everyday unit for body weight, shipping, and product weight in the United States.
Pound
Common for body weight, luggage, parcels, gym plates, and US product labels.
Ounce
Common for small package weights, food portions, postal weight, and consumer goods.
Stone
Common for body weight in some UK and Irish contexts, equal to 14 pounds.
When to use each unit
Choose the unit that matches the scale and audience. Use grams for small quantities, kilograms for body and package weights, pounds for US-facing weight labels, and metric tons for large industrial quantities.
Weight unit scale
Common unit mistakes
- Using pound as if it always means force. In everyday conversion, pound usually means pound-mass.
- Rounding 1 kg to 2.2 lb too early when precise shipping or fitness records matter.
- Confusing ounces of weight with fluid ounces of volume.
- Confusing metric ton, US short ton, and imperial long ton.
- Mixing grams and milligrams in medicine, nutrition, or lab work.
Available weight guides
The first weight guides cover kilogram and pound because they anchor the highest-demand metric and customary weight conversion pages.
Related converters
Use converter pages when you need a direct numerical answer.