Weight Converter Free Online
Convert between metric and imperial weight (mass) units instantly. Supports milligram, gram, kilogram, metric ton, ounce, pound, stone, US ton, and UK ton.
All Conversions
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How It Works
Enter a Value
Type the weight value into the From input. Both decimals (e.g. 1.5) and very small or very large values (e.g. 0.000001 or 1500000) are handled. The conversion runs live on every keystroke.
Pick Source & Target Units
Use the dropdowns to choose source and target units. The swap button between the panels flips both units (and values) instantly — useful for verifying round-trip accuracy or quickly switching from "I have kg, want lb" to "I have lb, want kg".
See All Conversions
The All Conversions panel below shows your input value converted into every supported unit at once. Useful for shipping (where a parcel weight may need to be quoted in both kg and lb) or for cooking (where a recipe in grams may need to be checked against a kitchen scale set to ounces).
Weight Converter Features
Metric Units
Full SI metric coverage: milligram, gram, kilogram, metric ton. All conversions go through kilograms as the base unit. The metric ton (1000 kg) is sometimes written tonne in international contexts; do not confuse with US or UK tons.
Imperial / US Units
Ounce (oz), pound (lb), stone (st), US short ton, UK long ton. The pound is defined as exactly 0.45359237 kg by international agreement (1959). 1 stone = 14 lb (used for body weight in the UK), 1 US short ton = 2000 lb = 907.185 kg, 1 UK long ton = 2240 lb = 1016.047 kg.
Three Different Tons
Be careful! There are three different tons: metric ton = 1000 kg (most common worldwide), US short ton = 907 kg (used in the US), and UK long ton = 1016 kg (legacy UK / shipping). Always check which one you mean. Cargo, freight, and emissions data often use the metric ton.
Live Conversion
The result updates instantly as you type. The All Conversions panel updates simultaneously so you can see all 9 units at once — useful for cross-checking shipping documents or recipes that mix unit systems.
Mass vs. Weight
Strictly speaking, the kilogram measures mass (the amount of matter), and weight is the gravitational force on that mass — measured in newtons. In everyday English, "weight" is used loosely to mean mass, which is what this converter calculates. For physics homework that explicitly asks for weight, multiply mass in kg by 9.80665 to get newtons.
100% Private
All conversion math runs locally in your browser. No values are transmitted anywhere. Safe for shipping quotations, manufacturing specs, or any other commercially sensitive weight data.
Free vs Pro
| Feature | Free | Pro |
|---|---|---|
| All 9 weight units | ||
| Live conversion | ||
| All-units result table | ||
| Bulk CSV / Excel conversion | — | |
| REST API access | — | |
| Custom precision settings | — |
Frequently Asked Questions
The international avoirdupois pound is defined as exactly 0.45359237 kilograms by an international agreement signed in 1959 by the US, UK, Canada, Australia, New Zealand, and South Africa. Before 1959, US and UK pounds had slightly different definitions, so historical documents may have tiny discrepancies. The pound used in everyday weight is the avoirdupois pound; the troy pound (used for precious metals) is different (= 12 troy ounces ≈ 373 g).
A stone is 14 pounds (about 6.35 kg). It is rarely used outside of the UK and Ireland, where it is the conventional unit for personal body weight (e.g. "11 stone 4 pounds"). Most other English-speaking countries use either kilograms (metric world) or just pounds (US). Conversion: 1 stone = 14 lb = 6.350 kg.
Mass is the amount of matter in an object — the same on Earth, on the Moon, and in space. Weight is the gravitational force on that mass — about 6 times less on the Moon than on Earth. Kilograms, pounds, etc. all technically measure mass, but in everyday English they are used loosely to mean weight. For physics calculations that explicitly need force, multiply by g (9.80665 m/s² on Earth) to get newtons.
Yes — both use the avoirdupois pound (453.592 g). The only place you might see a different "pound" is in precious metals (troy pound = 373.242 g) and in some historical apothecary recipes (apothecary pound = 373.242 g). Modern cooking, body weight, shipping, and groceries all use avoirdupois.
A handy approximation: multiply kilograms by 2.2 to get pounds (the exact factor is 2.2046). For example, 70 kg × 2.2 ≈ 154 lb (true value 154.32 lb). For pounds to kilograms, divide by 2.2 (or multiply by 0.45 for a rougher estimate). The mental approximation is accurate to about 0.2% — fine for personal use, not fine for engineering.