Weight & Mass Converter
Convert between kg, lbs, oz, grams, stones, and more.
Weight and mass measurements are central to cooking, shipping, medicine, and science. The difference between mass (how much matter an object contains) and weight (the force gravity exerts on it) matters in physics but is often used interchangeably in everyday life. Globally, the metric kilogram dominates, but pounds and ounces remain deeply embedded in US daily life — from grocery shopping to body weight to baby measurements.
Popular Weight & Mass Conversions
Standards Note: The Kilogram Is Constant-Based
NIST notes that since May 20, 2019, the kilogram has been defined through the Planck constant rather than a physical metal prototype, strengthening worldwide traceability.
Source: Kilogram: The Future | NIST
Pounds, Kilograms, and the Global Divide
The pound has roots in Roman and medieval trading systems. The modern avoirdupois pound (used for everyday goods) equals exactly 453.592 grams. Kilograms became the SI base unit of mass in 1889 when the International Prototype of the Kilogram — a platinum-iridium cylinder in France — was adopted. In 2019, the kilogram was redefined in terms of Planck's constant, anchoring it to fundamental physics rather than a physical artifact. Practically speaking: when a European recipe calls for 500 g of flour, that's just over 1 pound (17.6 oz).
Body Weight and BMI
Body weight is one of the most common conversion scenarios. Americans weigh themselves in pounds; most health guidelines and medical literature use kilograms. If you weigh 165 lbs, that is approximately 74.8 kg. In the UK, stone is still widely used — one stone equals 14 pounds, so a 165 lb person is 11 stone 11 lbs. BMI formulas require metric units, so converting to kilograms and meters is a necessary first step for accurate health calculations.
| Unit | Equivalent |
|---|---|
| 1 lb | 453.6 g / 0.4536 kg |
| 1 kg | 2.205 lbs |
| 1 oz (avoirdupois) | 28.35 g |
| 1 stone | 14 lbs / 6.35 kg |
| 1 ton (US short) | 2,000 lbs / 907.2 kg |
| 1 tonne (metric) | 1,000 kg / 2,205 lbs |
Cooking and Kitchen Weights
Professional bakers around the world weigh ingredients in grams for consistency — a cup of flour can vary by 20-30% depending on how it's scooped, while 120 grams is always 120 grams. Most US home recipes use cups and tablespoons, but online recipes from the UK, Australia, and Europe frequently call for weights in grams or ounces. Having a kitchen scale that shows both units eliminates guesswork. For small quantities, 1 ounce ≈ 28 grams is a useful mental benchmark.
Metric system: units of weight | 4th grade | Khan Academy
This Khan Academy lesson covers the metric weight ladder and gives a quick refresher on how mass units scale from milligrams to kilograms.
Video source: Khan Academy
Further Reading
Sources & References
- NIST — Units and Conversion Factors — Official US unit conversion factors from the National Institute of Standards and Technology.
- BIPM — The International System of Units (SI) — SI unit definitions from the International Bureau of Weights and Measures.