Converting pounds to kilograms is one of the most common weight calculations in everyday life — whether you are reading a US recipe, comparing gym lifts, filling in a medical form, or shipping a parcel internationally. This converter handles all of it: type a decimal pound value, or switch to the classic UK stone and pounds entry, and every equivalent is shown instantly.
How it works
The converter is built on a single exact constant: 1 lb = 0.45359237 kg. This figure was fixed by international agreement in 1959 and is the legal definition in the UK, US, Australia and Canada. Everything else derives from it:
| Relationship | Exact value |
|---|---|
| 1 lb to kg | 0.45359237 kg |
| 1 kg to lb | 2.204 622 621 8… lb |
| 1 stone | 14 lb = 6.350 293 18 kg |
| 1 ounce (oz) | 1/16 lb = 0.028 349 523 g |
| 1 US (short) ton | 2 000 lb = 907.184 74 kg |
Internally the tool converts your input to kilograms and then expresses that same mass in every unit simultaneously. No rounding is applied until the display step, where values are shown to four decimal places (kilograms) or two decimal places (grams, ounces) to stay readable without sacrificing accuracy.
Worked example
How many kg is 175 lb?
175 × 0.45359237 = 79.3787 kg
Broken down as stone and pounds: 175 lb ÷ 14 = 12 remainder 7, so 12 st 7 lb.
How many lb is 80 kg?
80 ÷ 0.45359237 = 176.370 lb (12 st 8.37 lb)
Quick mental estimate: multiply kilograms by 2.2 for pounds (slightly under-reports by ~0.2%). For stones, divide kilograms by 6.35.
Formula note
The primary formula is:
kg = lb × 0.45359237
The reciprocal is:
lb = kg ÷ 0.45359237 = kg × 2.204 622 621 848 776…
The reciprocal is irrational (it does not terminate), which is why going from kilograms back to a “nice” pound value can produce long decimals. The converter carries full floating-point precision throughout and only rounds at the point of display.
Stone entry works by first computing total pounds = (stone × 14) + remainder pounds, then applying the same formula. The stone-and-pounds breakdown shown for decimal input is computed by floor dividing the total pounds by 14 to get whole stones, with the leftover as the pounds part.
Common reference values
| Pounds (lb) | Kilograms (kg) | Stone + lb |
|---|---|---|
| 100 lb | 45.36 kg | 7 st 2 lb |
| 130 lb | 58.97 kg | 9 st 4 lb |
| 150 lb | 68.04 kg | 10 st 10 lb |
| 175 lb | 79.38 kg | 12 st 7 lb |
| 200 lb | 90.72 kg | 14 st 4 lb |
| 250 lb | 113.40 kg | 17 st 12 lb |
All figures above are calculated using the exact factor and rounded to two decimal places for the table only. The live converter above shows four decimal places.