What this calculator does
Change a weight from one unit to another, such as pounds to kilograms or ounces to grams. Pounds and kilograms are linked by one exact number. Since 1959, the international pound has been defined as exactly 0.45359237 kilograms.
Ounces, stones and tons are all fixed multiples of the pound, so every conversion here is exact. Enter an amount and pick your units. You'll see the answer, plus a table of the same amount in all nine units.
Where it's used
Why this math matters outside the classroom:
- Kitchen scales. Home cooks with a US recipe read a 1.2 kg chicken as about 2 lb 10 oz.
- Pallet loads. A pallet of half a metric tonne weighs about 1,102 lb.
- Body weight. A weight of 165 lb is about 74.8 kg, or 11 st 11 lb.
- Metric units. Students convert 2.5 kg to 2,500 g by staying inside the metric system.
- Postal weights. A 12 oz parcel weighs about 340 g, or 0.34 kg.
Grade level and standards: Grades 5–6; Common Core State Standards for Mathematics 5.MD.A.1, 6.RP.A.3.d. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Enter the amount to convert. Zero and decimals are fine, but negative numbers aren't.
- Choose the unit to convert from and the unit to convert to.
- Read the answer, or use the table to compare the amount in every unit.
What the inputs mean
- Weight (mass)
- The amount to convert, in the “From” unit.
- From
- The unit your number is in. Ounces here are ordinary (avoirdupois) ounces, 16 to the pound.
- To
- The unit you want the answer in. A “metric tonne” is 1,000 kg. US short tons and imperial (British) long tons are listed separately.
Formula and method
result = value × (size of the from-unit in kg) ÷ (size of the to-unit in kg) 1 lb = 0.45359237 kg (exact) 1 oz = 1/16 lb = 28.349523125 g 1 st = 14 lb = 6.35029318 kg 1 short ton = 2,000 lb = 907.18474 kg 1 long ton = 2,240 lb = 1,016.0469088 kg 1 t = 1,000 kg; 1 kg = 1,000 g; 1 g = 1,000 mg
In the formulas, lb is pounds, oz is ounces, st is stones, t is metric tonnes, kg is kilograms, g is grams and mg is milligrams. Each unit is stored as its exact size in kilograms. To convert, the calculator multiplies by the size of the unit you start with. Then it divides by the size of the unit you want. Nothing is rounded along the way.
The US short ton (2,000 lb) and the imperial long ton (2,240 lb) are different units. Both differ from the metric tonne of 1,000 kg, which is about 2,204.6 lb.
Worked example
Convert 150 pounds to kilograms.
- 1 pound is exactly 0.45359237 kg.
- 150 × 0.45359237 = 68.0388555.
Result: 150 lb is 68.0388555 kg, or about 68.04 kg. Going the other way, 1 kg is about 2.20462 lb.
Understanding the result
For quick estimates, 1 kg is a little over 2.2 lb, and 1 oz is a little over 28 g.
In the UK and Ireland, body weight is often given in stones and pounds. 10 st 7 lb is 10 × 14 + 7 = 147 lb.
Assumptions and limitations
- Pounds and ounces are the international avoirdupois units, the ones used every day.
- “Ton” means the US short ton or the imperial long ton, as labeled. “Tonne” means the metric tonne.
- Troy ounces and troy pounds, used for gold and other precious metals, aren't included. A troy ounce is heavier than an ordinary ounce.
- It converts mass only. Turning a volume (such as cups) into a weight needs the substance's density (how heavy it is for its size). This tool doesn't use density.
Frequently asked questions
Is this converting weight or mass?
Strictly speaking, mass. Mass is the amount of matter in an object, and it doesn't change from place to place. Weight is the pull of gravity on that mass. In everyday use, “weight” means mass in kilograms or pounds, and that's what this tool converts.
How many pounds are in a kilogram?
About 2.2046226. It's 1 divided by the exact definition, 1 lb = 0.45359237 kg, so it never ends in a round number.
How many pounds are in a stone?
Exactly 14, which makes one stone 6.35029318 kg.
What's the difference between a ton and a tonne?
A US short ton is 2,000 lb (about 907 kg). An imperial long ton is 2,240 lb (about 1,016 kg). A metric tonne is 1,000 kg (about 2,205 lb). Check which one a figure uses before converting.
Is there a page for a single pair, such as kg to lbs?
Yes. The most common weight conversions have their own pages, each with a table of typical values and tips for that pair. They are kilograms to pounds, ounces to grams, grams to pounds, ounces to pounds, stone to kilograms, stone to pounds and US tons to pounds. Use this converter for any other combination.
How this calculator is checked
Method: International yard and pound agreement (1959): 1 lb = 0.45359237 kg exactly; customary multiples (16 oz, 14 lb stone, 2,000 lb short ton, 2,240 lb long ton); SI prefixes. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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