Free Weight Converter
Convert weight and mass units instantly — kilograms, pounds, grams, ounces, tonnes, and more. Type into any field and all others update. Free, symmetrical, no sign-up.
Exact Conversion Formula & Multipliers
Mass conversions anchor on 1 pound = 0.45359237 kilograms — an exact value fixed by international agreement in 1959 — from which 1 ounce = 28.349523125 grams and 1 stone = 6.35029318 kilograms are derived directly. The kilogram itself, historically tied to a physical platinum-iridium cylinder in France, was redefined in 2019 using the Planck constant, so today's conversions rest on a fixed physical law rather than a guarded metal object.
Practical Real-World Scenarios
- Shipping and logistics: international couriers bill by kilograms while US carriers quote pounds, so cross-border invoices need both figures reconciled.
- Nutrition and fitness: food labels list grams per serving in most countries but ounces in the US, and gym-goers tracking body weight often switch units when using apps built for a different region.
- Cooking: baking recipes from European sources specify grams for precision, while many American recipes still use ounces or pounds for ingredients like flour and meat.
Historical & Technical Background
The pound descends from the Roman libra, while the avoirdupois pound used in English-speaking countries today was standardized in the 13th–16th centuries for trade. The metric gram and kilogram emerged from the same 1795 French revolutionary effort that produced the meter, intended as a universal, decimal-based alternative to the patchwork of local weight standards then in use across Europe. That decimal structure is why metric mass conversions are simple powers of ten, while imperial units (16 ounces to a pound, 14 pounds to a stone) are not.
Precision & Accuracy Statement
Conversion factors use the exact defined values given in NIST Special Publication 811 and the BIPM SI Brochure wherever such a definition exists (for example 1 lb = 0.45359237 kg, 1 in = 2.54 cm, 1 US gal = 3.785411784 L, g₀ = 9.80665 m/s²); derived factors are computed from those definitions rather than copied as rounded figures. Results are calculated in double-precision floating point and shown to 10 significant digits, so the last digit can differ by one unit of rounding. The rounded figures in the text and tables above are for reading convenience.
How This Converter Works
Weight is expressed in kilograms across most of the world, but pounds and ounces remain common in the US, UK, and for many consumer products. Our converter handles 9 units including stone, US ton, and microgram.
Common Conversions
| Kilograms (kg) | Pounds (lbs) | Grams (g) | Context |
|---|---|---|---|
| 0.0283 kg | 0.0625 lb | 28.35 g | One ounce |
| 0.4536 kg | 1 lb | 453.6 g | One pound |
| 1 kg | 2.205 lbs | 1,000 g | One kilogram |
| 6.35 kg | 14 lbs | 6,350 g | One stone |
| 23 kg | 50.7 lbs | 23,000 g | Standard checked luggage limit |
| 100 kg | 220.5 lbs | 100,000 g | Quintal (100 kg) |