Common Weight Units Explained: From Milligrams to Metric Tons

5 min read•June 2, 2026•Reviewed: June 2, 2026

✓Reviewed by Apex Conversion Editorial Team · Last reviewed June 2, 2026

Weight and mass are measured using a variety of units across different contexts and measurement systems. From the tiny milligram used in pharmaceutical dosing to the metric ton used in industrial shipping, each unit serves a specific range of practical applications. This guide covers every common weight unit — its definition, typical uses, and how it relates to others.

Understanding these units helps you read international product labels, work with recipes from other countries, interpret medical prescriptions, and navigate between the metric and US customary systems confidently.

Metric Weight Units

Milligram (mg): 1/1,000 of a gram. Used for pharmaceutical doses, vitamin content on nutrition labels, and chemistry. A standard aspirin tablet is 325 mg. Gram (g): the fundamental practical unit in cooking and chemistry. 1 g = 1,000 mg. A paperclip weighs about 1 g. Kilogram (kg): the SI base unit. 1 kg = 1,000 g. A liter of water weighs 1 kg. The most widely used weight unit worldwide. Metric tonne (t): 1,000 kg = 2,204.62 lb. Used for cargo, industrial materials, and large-scale measurements.

The metric system's key advantage is its decimal structure: every unit is 1,000× larger or smaller than the adjacent one. This makes conversions entirely a matter of moving the decimal point. A 2,500 mg dose = 2.5 g = 0.0025 kg.

US Customary and Imperial Weight Units

Ounce (oz): 1/16 of a pound = 28.3495 g. Used for food portions, precious metals (troy ounce = 31.10 g), and product weight in the US. A slice of bread is about 1 oz. Pound (lb): the primary US weight unit = 16 oz = 453.592 g. Common for body weight, groceries, and industrial specifications in the US. Stone (st): 14 lb = 6.35 kg. Used in the UK/Ireland for body weight. Short ton: 2,000 lb = 907.185 kg. Used in the US for cargo and industrial quantities. Long ton: 2,240 lb = 1,016.05 kg. Historically used in the UK.

Quick Reference Conversions

1 mg    = 0.001 g
1 g     = 1,000 mg = 0.035274 oz
1 oz    = 28.3495 g
1 lb    = 16 oz = 453.592 g = 0.453592 kg
1 kg    = 1,000 g = 2.20462 lb = 35.274 oz
1 stone = 14 lb = 6.35029 kg
1 t (metric) = 1,000 kg = 2,204.62 lb
1 ton (US short) = 2,000 lb = 907.185 kg
1 ton (UK long)  = 2,240 lb = 1,016.05 kg

Frequently Asked Questions

What is the smallest common weight unit?

In everyday use, the milligram (mg) is the smallest common weight unit, used for pharmaceutical doses and micronutrients on food labels. In scientific contexts, micrograms (μg = 0.001 mg) and nanograms are used.

How many grams are in a pound?

1 pound = 453.592 grams. Or: 1 kg = 2.20462 lb, so 1 lb = 1,000 ÷ 2.20462 = 453.592 g.

What unit is used for very large weights?

Metric tonnes (1,000 kg) for international cargo and industrial applications. In the US, the short ton (2,000 lb) is used. For extremely large quantities (ore, agricultural production), kilotons and megatons may be used.

Which weight unit is best for cooking?

Grams for precision baking (especially for small amounts of ingredients like yeast, salt, or leavening). Kilograms for larger quantities. Ounces and pounds for US recipes. Weighing with a kitchen scale is more accurate than measuring by volume for baking.

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