Force converter

A kilo is not a force

This is the confusion nearly all the difficulty with these units comes from. The kilogram is a mass: it says how much matter there is, and it stays the same on Earth, on the Moon and in space. The newton is a force: on Earth, a kilo of mass presses with a force of about 9.81 N, on the Moon with a sixth of that. When a hook says «capacity 50 kg», what's meant is the weight force of fifty kilos, about 490 newtons: it's a practical way of speaking, but it isn't the same quantity.

The units you actually meet

The kgf (kilogram-force, or kilopond in German texts) is exactly the weight force of a kilo: 9.81 N. The daN, decanewton, is 10 N and is almost identical to the kgf (1 kgf = 0.981 daN): that's why it appears on tow hooks, ropes and harnesses, where reading «500 daN» as «about 510 kilos» is convenient and practically correct. The lbf, pound-force, is 4.45 N. The dyne is a crumb, a hundred-thousandth of a newton, and survives only in some old physics texts.

How much is a newton

Not much: it's roughly the force with which a hundred-gram apple presses on your hand — the image is the one from the Newton story, and for once it's useful. From there the other numbers make sense: a 70 kg adult presses on the floor with about 690 N, and a one-and-a-half-tonne car with nearly 15,000 N, that is 15 kN.

Nearby tools

For tightening torque, which is a force times a lever, there is Torque converter; for pressure, which is a force per unit of area, Pressure converter. For masses the page is Weight converter and for energy Energy converter.