156+ conversions · 13 units
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Welcome to the ConvertNow weight & mass converter hub. Whether you are a student solving homework, a professional completing a project, or a traveller navigating unfamiliar units, our free weight & mass conversion tools give you instant, accurate results backed by internationally verified constants.
Weight measurement traces back to grain seeds and carob seeds used as balance-scale weights over 5,000 years ago. The Roman libra gave us the pound. In 1795 the gram was defined from a cubic centimetre of water. The kilogram was the last SI base unit tied to a physical artefact — a platinum-iridium cylinder in Sèvres — until 2019, when it was redefined using Planck's constant.
Weight conversions protect health (medication dosing), commerce (shipping costs), and safety (aircraft load limits). A 1 kg mistake in luggage fees can cost travellers; a 0.1 g error in pharmaceutical compounding can be dangerous.
Pharmacists, nutritionists, fitness trainers, logistics managers, jewelers, and home cooks.
Pounds vs kilograms (1 lb ≈ 0.454 kg) and ounces vs grams (1 oz ≈ 28.35 g). Many people estimate 1 kg ≈ 2 lb, which is close enough for luggage but inaccurate for medicine.
| Unit | Symbol | Base Equivalent | Common Use |
|---|---|---|---|
| Kilogram | kg | 1 kg | Global (SI) |
| Gram | g | 0.001 kg | Global |
| Milligram | mg | 1e-6 kg | Pharmacy |
| Metric Tonne | t | 1,000 kg | Shipping |
| Pound | lb | 0.4536 kg | US, UK |
| Ounce | oz | 0.02835 kg | US, UK |
| Stone | st | 6.350 kg | UK, Ireland |
| Common Value | Equals |
|---|---|
| 1 lb | 0.454 kg |
| 1 oz | 28.35 g |
| 1 stone | 6.35 kg |
| 1 tonne | 2,205 lb |
Mass is the amount of matter (kilograms). Weight is the force of gravity on that mass (newtons). On Earth they are proportional and often used interchangeably in everyday language.
1 pound = 453.59237 grams exactly (by international agreement since 1959).
Medical standards follow the SI system (kilograms). US fitness culture historically adopted pounds. Most modern gyms display both.
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