The Pounds to Kilograms Calculator converts a weight in pounds into kilograms using the exact international avoirdupois definition, 1 pound equals 0.45359237 kilograms. Enter a value in pounds, and the tool multiplies by that factor, showing the substitution so the result can be checked by hand.
Pounds remain the everyday weight unit in the United States, while kilograms are standard almost everywhere else and in scientific and medical contexts worldwide. This page leads with the pounds-to-kilograms direction, the one most often needed when a US weight figure has to be reported or compared internationally.
Convert pounds to kilograms
To convert pounds to kilograms, multiply the pound value by 0.45359237.
kilograms = pounds × 0.45359237Worked example: convert 150 lb to kilograms.
1. Multiply by 0.45359237. 150 × 0.45359237 = 68.0388555 kg.
So 150 lb equals about 68.04 kg. The factor 0.45359237 is exact by international agreement, dating from a 1959 agreement among English-speaking countries that standardized the pound at exactly that fraction of a kilogram, so no rounding error exists in the factor itself.
Understand where the exact factor comes from
Before 1959, different countries used slightly different definitions of the pound, which caused small but real discrepancies in international trade and science. The International Yard and Pound Agreement fixed the international avoirdupois pound at exactly 0.45359237 kilograms, a definition still in use today.
That is why pound-to-kilogram conversions can be treated as exact rather than approximate, unlike some historical unit conversions that carry genuine measurement uncertainty.
Check common weight conversions
| Pounds | Kilograms |
|---|---|
| 1 lb | 0.4536 kg |
| 10 lb | 4.5359 kg |
| 50 lb | 22.6796 kg |
| 100 lb | 45.3592 kg |
| 150 lb | 68.0389 kg |
| 200 lb | 90.7185 kg |
Each figure is the pound value multiplied by 0.45359237 and rounded to four decimal places, which is more precision than most everyday uses require but useful for verifying the calculator's output.
Convert kilograms back to pounds
The Pounds to Kilograms Calculator also runs the reverse direction. To convert kilograms to pounds, divide by 0.45359237, which is the same as multiplying by 2.2046226218.
pounds = kilograms ÷ 0.45359237Worked example: convert 70 kg to pounds.
1. Divide by 0.45359237. 70 ÷ 0.45359237 ≈ 154.32 lb.
That figure, roughly 154.3 pounds for a 70 kg weight, is a commonly cited body-weight reference point in fitness and medical contexts that switch between metric and imperial units.
Watch for the ounce and stone variations
Pounds are sometimes broken down further into ounces (16 ounces to a pound) or grouped into stone (14 pounds to a stone) in UK usage. A weight given as "10 stone 5 pounds" first needs converting to a single pound figure, 10 × 14 + 5 = 145 lb, before the kilogram formula applies: 145 × 0.45359237 ≈ 65.77 kg.
Mixing up stone-and-pounds with a plain pound figure is a common source of error when converting UK body-weight figures.
Convert a lighter and a heavier example
Checking the formula at both ends of a typical weight range confirms it holds outside the 1-to-200-pound table above. Worked example: convert 25 lb to kilograms. 1. Multiply by 0.45359237. 25 × 0.45359237 ≈ 11.34 kg. Worked example: convert 500 lb to kilograms.
1. Multiply by 0.45359237. 500 × 0.45359237 ≈ 226.80 kg.
Both results use the exact same factor as the 150 lb example earlier on this page, so 25 lb becomes about 11.34 kg and 500 lb becomes about 226.80 kg, regardless of whether the weight is a small parcel or a heavy piece of equipment.
Convert pounds and ounces together
A weight is sometimes given as pounds plus a remainder in ounces, such as "8 lb 6 oz" for a newborn's birth weight. Converting that figure first means turning the ounces into a decimal fraction of a pound, since 16 ounces make one pound.
Worked example: convert 8 lb 6 oz to kilograms.
1. Convert ounces to a fraction of a pound. 6 ÷ 16 = 0.375 lb.
2. Add to the whole pounds. 8 + 0.375 = 8.375 lb.
3. Multiply by 0.45359237. 8.375 × 0.45359237 ≈ 3.80 kg.
So a birth weight of 8 lb 6 oz converts to approximately 3.80 kg, using the same multiplication as any other pound figure once the ounces are folded into a single decimal value. Skipping that fraction step and multiplying 8.6 directly instead of 8.375 would produce a noticeably wrong result, since 6 ounces is not the same as 0.6 of a pound.
Frequently asked questions
What is the formula to convert pounds to kilograms?
Multiply the pound value by 0.45359237: kilograms = pounds × 0.45359237. For example, 150 lb converts to 150 × 0.45359237 ≈ 68.04 kg.
How do you convert kilograms back to pounds?
Divide the kilogram value by 0.45359237, or equivalently multiply by 2.2046226218: pounds = kilograms ÷ 0.45359237.
Is the pound-to-kilogram conversion exact?
Yes. Since 1959, the international avoirdupois pound has been defined as exactly 0.45359237 kilograms, so the factor itself carries no rounding uncertainty.
What is 1 pound in kilograms?
1 pound equals 0.45359237 kilograms, or about 0.4536 kg when rounded to four decimal places.
What is 70 kg in pounds?
70 kg equals approximately 154.32 pounds, a figure often referenced as a typical adult body weight.
How do you convert stone and pounds to kilograms?
Multiply the stone figure by 14, add the remaining pounds, then multiply the total by 0.45359237. For example, 10 stone 5 pounds is 145 lb, which converts to about 65.77 kg.
Does this calculator handle other weight units like ounces or metric tonnes?
Yes. Related tools such as the Weight Converter cover ounces, stone, metric tonnes and other units within the same weight-conversion family.
Summary
Pounds convert to kilograms by multiplying by the exact factor 0.45359237, so 150 lb becomes about 68.04 kg and 70 kg becomes about 154.32 lb in reverse. That factor has been fixed by international agreement since 1959, making the conversion exact rather than approximate.
Stone-and-pounds figures need converting to a single pound value first, by multiplying stone by 14 and adding the remainder, before applying the standard formula.