Weight Converter: Kg, Pounds, Ounces & Stone
Convert between kilograms, grams, pounds, ounces, stone, tonnes, and US/UK tons, instantly and precisely, right in your browser.
How this weight converter maps nine mass units to the kilogram, and where stone and long tons come from
Mass is one of the few quantities where the SI base unit, the kilogram, is also the everyday unit most of the world already uses. Everything in this tool converts against it, which keeps the arithmetic simple even though the unit names themselves carry a lot of regional history, particularly stone, and the split between short and long tons.
The tool runs entirely in your browser using plain JavaScript. Nothing you type is sent to a server.
How a weight conversion runs
| Unit | Symbol | Kilograms per unit |
|---|---|---|
| Milligram | mg | 0.000001 |
| Gram | g | 0.001 |
| Kilogram | kg | 1 |
| Metric tonne | t | 1,000 |
| Ounce | oz | 0.028349523125 |
| Pound | lb | 0.45359237 |
| Stone | st | 6.35029318 |
| US ton (short ton) | ton | 907.18474 |
| UK ton (long ton) | ton | 1,016.0469088 |
Where the pound and stone actually come from
The international avoirdupois pound
Fixed by international agreement in 1959 at exactly 0.45359237 kilograms. Every imperial mass unit in this tool, ounce, stone, and both ton variants, derives from that single fixed pound definition rather than being independently defined.
The stone
Set at exactly 14 pounds, or 6.35029318 kilograms. Still in common everyday use for body weight in the UK and Ireland, even though it has been out of official trade use for decades in favor of the kilogram.
Mass unit references
- BIPM SI Brochure defines the kilogram as the SI base unit of mass, redefined in 2019 in terms of the fixed Planck constant.
- NIST reference on the international pound documents the exact 1959 agreement fixing the pound at 0.45359237 kilograms.
- UK Weights and Measures Act covers the stone and long ton as units still recognized in UK trade and customary use.
Mass and weight in daily use
Converting a UK body weight reading in stone into kilograms for a medical form, checking a shipping manifest’s short ton figure against a metric tonne quota, translating a US recipe’s ounce measurements into grams for a kitchen scale, working out a vehicle’s kerb weight between pounds and kilograms for import paperwork, and reconciling an industrial cargo weight between long tons and metric tonnes on international freight documents.
FAQ: Weight Converter
Multiply the kilogram value by 2.20462 to get pounds (or divide by 0.45359237, the more precise factor this tool uses). For example, 70 kg equals approximately 154.3 lbs. This is one of the most common conversions for body weight, since many countries use kg while the US commonly uses lbs.
A stone is a traditional British unit of weight equal to exactly 14 pounds, still commonly used in the UK and Ireland for expressing body weight (for example, ’11 stone 4′ means 11 stone plus 4 additional pounds). One stone equals approximately 6.35 kg.
A US ton (short ton) equals 2,000 pounds (about 907.18 kg), while a UK ton (long ton) equals 2,240 pounds (about 1,016.05 kg), roughly 12% heavier. This distinction matters in international shipping, freight, and bulk commodity trading, where using the wrong ton definition can cause significant billing or weight-limit errors.
One ounce equals approximately 28.35 grams. This conversion is especially common in cooking and baking recipes, where US recipes often use ounces or cups while metric recipes specify grams, and precise baking in particular benefits from exact gram measurements rather than approximate volume units.
In everyday language and in this tool, weight and mass are used interchangeably, since on Earth’s surface they’re proportional and convert using the same standard factors. Technically, mass measures the amount of matter in an object (constant everywhere) while weight measures the force of gravity acting on that mass (which would differ on the Moon or in orbit), but standard units like kilograms and pounds are used for both in nearly all practical, non-scientific contexts.
The factors used here are the internationally defined exact conversion constants, 1 pound equals exactly 0.45359237 kg by international agreement, and every other imperial unit in this tool derives from that same exact pound definition, so results are accurate to full floating-point precision, not rounded estimates.
From the blog
Reading around units
Where measurement systems came from and why two of them still argue.
