What this calculator does
A kilogram measures mass, the amount of matter in an object, and a newton measures force, specifically the weight force gravity exerts on that mass. The two are related by a single multiplication: weight in newtons equals mass in kilograms times the local gravitational acceleration, which on Earth is close to 9.80665 m/s². This converter handles both kg to newtons and the reverse.
The mix-up between mass and weight is common because everyday speech treats them as the same thing: a "75 kg person weighs 75 kg." In physics they are not interchangeable. Mass stays the same everywhere; weight, the force in newtons, changes with gravity. The same 75 kg mass weighs about 736 N on Earth and roughly a sixth of that on the Moon.
The formula
Multiply mass in kilograms by the gravitational acceleration in metres per second squared to get weight in newtons. To go the other way, divide the weight force in newtons by the same gravitational acceleration to recover the mass in kilograms.
| Term | Meaning |
|---|---|
| Mass | The amount of matter in an object, in kilograms, independent of gravity. |
| Weight force | The force gravity exerts on that mass, in newtons: mass × gravitational acceleration. |
| Gravitational acceleration (g) | Standard Earth gravity is 9.80665 m/s². The field is editable so the same conversion works for the Moon (about 1.62 m/s²), Mars (about 3.71 m/s²), or a specific local value. |
The inputs explained
| Field | What to enter |
|---|---|
| Direction | Choose from Kilograms to newtons, Newtons to kilograms. |
| Mass (kg) or weight force (N) | Enter the mass in kilograms, or the weight force in newtons, depending on the direction selected above. |
| Gravitational acceleration (m/s²) | Gravitational acceleration to use. Leave at 9.80665 m/s² for standard Earth gravity, or change it for another body or a specific local value. |
When to use it
Engineering and structural calculations
Loads are specified as a mass in kilograms, but structural formulas for force, stress and load-bearing capacity work in newtons, so the mass has to be converted to a weight force before it goes into the equation.
Checking a spec sheet
Product datasheets sometimes quote a maximum load in newtons rather than kilograms, or the other way round; converting both figures to the same unit makes them directly comparable.
Working out weight on another world
Changing the gravitational acceleration field to the Moon or Mars value converts the same kilogram mass into its weight force on that body, without changing the mass itself.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What do common masses weigh in newtons?
A range of everyday masses converted to their weight force on Earth.
How does the same mass weigh on Earth, the Moon and Mars?
A fixed 75 kg mass converted using different gravitational accelerations.
Questions
Why are kg and newtons not directly interchangeable?
Kilograms measure mass, an intrinsic property of an object that does not change with location. Newtons measure force, and weight force depends on both mass and the local gravitational acceleration, so the same mass gives a different newton figure on different planets.
What gravitational acceleration should I use for Earth?
The standard value is 9.80665 m/s², defined as standard gravity. Actual local gravity varies very slightly by latitude and altitude, but 9.80665 m/s² is the figure used in almost all everyday and engineering conversions.
How is this different from the gravitational force calculator?
The gravitational force calculator works out the attractive force between two masses using Newton's law of universal gravitation, which depends on both masses and the distance between them. This converter is the simpler everyday case: one mass, standard gravity, done.
Is 1 kg exactly equal to 9.8 N?
Approximately, at standard Earth gravity: 1 kg weighs 9.80665 N. It is a close approximation rather than an exact unit equivalence, because the newton figure depends on gravitational acceleration rather than being a fixed conversion factor like metres to feet.
For the gravitational pull between two masses rather than a simple weight conversion, see the gravitational force calculator. For force, mass and acceleration in Newton's second law more generally, see the related physics calculators on this site.