kN to kg: why a kilonewton is not a kilogram
A kilonewton is a force and a kilogram is a mass, so strictly speaking the two do not convert. Everyone converts them anyway, and on Earth the answer is 101.97 kilograms per kilonewton. Here is the division that produces it, and the moment it stops being true.
A force and a mass are not the same quantity
The newton measures a pull: one newton accelerates one kilogram by one meter per second squared. The kilogram measures matter, and it does not change when you carry it up a mountain or take it into orbit. A converter that turned one into the other without a word would be hiding an assumption rather than doing arithmetic.
The assumption is that the load hangs still at the surface of the Earth. Under that condition, and only under it, a force has a weight in kilograms, and the shortcut has a proper name: the kilogram-force, written kgf, which is exactly the pull of one kilogram under standard gravity.
The division, and the number worth remembering
Standard gravity was fixed by convention in 1901 at 9.80665 meters per second squared. Divide newtons by that number and you get kilogram-force. A kilonewton is a thousand newtons, so one kilonewton is 101.97 kilograms, near enough a tenth of a metric ton.
Read backwards, the same division answers the question people actually type: 100 newtons is 10.2 kilograms, and a 50 kN rating holds a little over five tons. The rough version, one kilonewton for a hundred kilograms, is 2 percent low, which is fine on a sketch and not fine on a safety margin.
Where the shortcut holds, and where it breaks
Gravity is not the same everywhere on Earth, but it varies little: 9.780 at the equator, 9.832 at the poles, a spread of half a percent. For a crane, a hoist, a climbing anchor or a bolt pulled out of concrete, the 101.97 figure is more precise than the load will ever be measured.
It breaks in two places. A load being accelerated pulls harder than its own weight, which is why lifting gear carries a working load limit well under its breaking force. And gravity elsewhere is not 9.80665: the same kilonewton holds six times more mass on the Moon, and none at all in free fall, where the mass is unchanged and the force reads zero.
Lowercase kn is a knot, not a kilonewton
The two symbols differ by one capital letter, and almost nobody types it. kN with a capital N is the kilonewton, a force. kn in lowercase is the knot, one nautical mile per hour, a speed, and a search box has to guess which one was meant.
If you came here for boat speed, the knot has its own page: one knot is 1.852 kilometers per hour exactly, because the nautical mile is defined as 1852 meters. If you came here for a load rating, you are on the right page.
Kilonewtons, and the mass they hold under standard gravity
| Force | Mass on Earth |
|---|---|
| 1 kN | 101.97 kg |
| 2 kN | 203.94 kg |
| 5 kN | 509.86 kg |
| 10 kN | 1,019.72 kg |
| 14 kN | 1,427.60 kg |
| 50 kN | 5,098.58 kg |
| 100 kN | 10,197.16 kg |
Each line divides the force by 9.80665. On another body, or on a load being accelerated, the second column no longer holds.
Frequently asked questions
How many kg is 1 kN?
1 kN is 101.97 kg on Earth, or 101.97 kgf to be exact about it. The figure comes from dividing 1000 newtons by the standard gravity of 9.80665.
How many kg is 100 newtons?
100 N is 10.2 kg. The same division applies: 100 divided by 9.80665 gives 10.197 kilogram-force, which a scale under the load would read as 10.2 kg.
Is kn the same as kg?
No. A kilonewton is a force and a kilogram is a mass, and one only becomes the other if you assume standard gravity on Earth. Watch the capital letter too: lowercase kn is the knot, a speed of 1.852 km/h.