Pounds-force to kilograms-force
One pound-force is 0.45359237 kilograms-force, and this shows the working rather than just the answer. Nothing you type here leaves your browser — it is worked out on your own device, so there is nothing to send and nothing to log.
The factor
One pound-force is 0.45359237 kilograms-force. That is the whole of the conversion: multiply by it, and nothing else happens.
What this page will not claim
It will not call this conversion exact. The factor is right to every figure shown, but at least one of these two units is not defined exactly in terms of the other, so there is a limit to how far the decimals mean anything.
The pound-force is a pound under standard gravity.
The kilogram-force is standard gravity is defined as exactly 9.80665 m/s², so this is exact too.
The number in your head
Most people use 0.45 for this, which is the factor to two significant figures. It is low by 0.792% — 7.92 kilograms-force too few in every thousand, and 79.2 in every ten thousand.
Going the other way
The reverse is not this sum backwards in your head. It is a different factor, 2.204622621849, and dividing by one is not the same as multiplying by a rounded version of the other.
Rounded, the way back is 2.2, which is low by 0.2097%. So the two roundings do not cancel: go out and back with both and you do not land where you started.
How many of those decimals mean anything
The box above will give you ten decimal places because it can. Whether they mean anything is decided by your measurement, not by the arithmetic.
If you measured to the nearest pound-force, your figure is already uncertain by half of one — so the answer is uncertain by about 0.226796 kilograms-force, and every digit past that is decoration. Quoting 0.559987 when you measured with a tape is claiming a precision the tape never had.
Where these two sit
Pounds-force and kilograms-force both measure force, which is why they can be converted at all. A conversion between families — a length into a weight — is not a conversion, it is a question with a missing quantity in it.
The unit converter pairs pounds-force with newtons rather than with kilograms-force, because that is the conversion people ask for most. This page exists because a good many ask for this one instead.