How this calculator works
Enter a weight in pounds or kilograms, pick the direction you want to convert, and the calculator applies the exact 0.45359237 kg-per-pound constant. For the pounds-to-stone direction, it splits the result into whole stone plus the leftover pounds instead of a single decimal figure.
The formula
kg = lb x 0.45359237 Inverse: lb = kg / 0.45359237 Stone: stone = floor(lb / 14) remainderLb = lb - stone x 14
Worked example
Converting 154 lb to kilograms:
- Kilograms: 154 x 0.45359237 = 69.85322498, rounded to 69.9 kg
Frequently asked questions (FAQ)
How many kilograms are in one pound?
Exactly 0.45359237 kilograms. This is the international avoirdupois pound definition set by the 1959 yard-and-pound agreement and used consistently across the United States, United Kingdom, Canada, and Australia, so it's the value this calculator uses for every conversion.
Why does this calculator use 0.45359237 kg exactly instead of a rounded value?
Rounding the constant itself (say, to 0.454) would introduce error that compounds across a whole weight, especially for heavier values. Using the exact 0.45359237 kg figure and only rounding the final displayed result keeps the answer as accurate as the input allows.
How do I convert pounds to kilograms by hand?
Multiply the weight in pounds by 0.45359237 to get kilograms. For example, 154 lb x 0.45359237 is 69.85322498, which rounds to 69.9 kg. To go the other way, divide the kilogram figure by the same constant.
How does the stone conversion work, and why 14 pounds?
One stone equals 14 pounds by definition, a unit still used for body weight in the United Kingdom and Ireland. The calculator divides your pounds by 14, keeps the whole number as stone, and shows the leftover pounds as the remainder, for example 160 lb is 11 stone 6 lb.
Why might converting kg back to lb not land on the exact number I started with?
Not every kilogram value divides evenly by 0.45359237. When it doesn't, the result is rounded to one decimal place for display, so converting back and forth can shift by a tenth of a pound. The underlying math is still exact.
Can I use this calculator for weights other than body weight?
Yes. The math is a straightforward mass conversion between pounds, kilograms, and stone, so it works for any weight in that range, not just body weight, as long as the value fits within the input limits above.