Pounds to Kilograms Converter
Convert lb to kg instantly with the exact factor — free, no sign-up.
Type a weight in pounds and get the exact kilogram equivalent instantly. The converter multiplies by the internationally defined factor of 0.45359237, shows the math, and lets you swap direction with one tap.
How it's calculated
kilograms = pounds × 0.45359237. The factor is exact: the international pound is legally defined as 0.45359237 kg.
How the pound-to-kilogram conversion works
The international avoirdupois pound is defined as exactly 0.45359237 kilograms, an agreement fixed in 1959 between English-speaking nations. Converting pounds to kilograms is therefore one multiplication: kilograms = pounds × 0.45359237. No rounding is hiding anywhere — the definition itself carries the full precision.
This single exact factor covers every pound-to-kilogram conversion you'll ever need, from a newborn's birth weight to freight tonnage. The converter above applies it directly, so its results match what a laboratory balance calibrated in SI units would read.
Common pound to kilogram reference points
A few anchors make mental estimates easy. One pound is about 0.45 kg, so 10 lb is 4.54 kg, 25 lb is 11.34 kg, and 50 lb is 22.68 kg — the numbers you'll meet on US luggage scales and gym plates.
Body-weight landmarks: 100 lb converts to 45.36 kg, 120 lb to 54.43 kg, 150 lb to 68.04 kg, 180 lb to 81.65 kg, 200 lb to 90.72 kg, and 250 lb to 113.40 kg. A 45 lb Olympic plate is 20.41 kg, which explains why metric plates are stamped 20 kg instead.
Where you'll use pounds to kilograms
Anyone reading a US cookbook, fitness plan, or product manual outside America hits this conversion constantly. Baby weights announced in pounds, NFL player stats, and US shipping labels all need translating for metric-system readers.
In medicine the stakes are higher: drug doses are calculated per kilogram of body weight, so converting a patient's weight from pounds must use the exact factor, never a rounded one. The same applies to checked baggage — a 50 lb airline limit is exactly 22.68 kg, and rounding down the allowance could cost you an overweight fee.
Frequently asked questions
What is the exact lb to kg conversion factor?
One pound equals exactly 0.45359237 kilograms by international definition (1959). Multiply any pound value by 0.45359237 for an exact kilogram result.
How do I convert lbs to kg in my head?
Halve the pounds and subtract about 10% of the result: 150 lb → 75 − 7.5 = 67.5 kg, close to the exact 68.04 kg. Or simply divide by 2.2 for a quick estimate.
How many kg is 150 lbs?
150 pounds is exactly 68.0388555 kg, usually rounded to 68.04 kg. Try it in the converter above — the answer appears as you type.
Is the pound the same everywhere?
The avoirdupois pound (0.45359237 kg) is the standard pound used in the US, UK, and internationally for commerce. Older troy pounds and apothecary pounds differ and are now rare outside precious-metals trading.