The weight formula
Weight is the gravitational force on a mass: W = m·g, where m is mass in kilograms and g is gravitational acceleration (9.8 m/s²). A 10 kg mass weighs 98 N on Earth. Weight changes with gravity, but mass does not. To find the energy of lifting that mass, see the potential energy calculator.
How to use this calculator
Enter the mass in kilograms. The calculator multiplies by g = 9.8 m/s² and returns weight in newtons (N). Weight is a force, not a mass, so its unit is the newton. For pressure from that weight on a surface, see the pressure calculator.
- Grams need converting — divide by 1,000 before entering a mass in grams.
- Bathroom scales show mass, not weight, even though everyday language calls it weight.
- Pounds are a weight unit, so convert to kilograms first by dividing by 2.205.
Worked example
A 10 kg bag of flour: 10 × 9.8 = 98 N. On the Moon, where g is about 1.6 m/s², the same mass would weigh only about 16 N, because weight depends on local gravity.
Even on Earth the figure is not perfectly fixed: g runs closer to 9.78 m/s² at the equator and 9.83 m/s² near the poles, so an object weighs a fraction of a percent more in Oslo than in Nairobi. On Mars, where g is about 3.7 m/s², the same 10 kg bag would push down with only 37 N. Engineers use weight rather than mass whenever they size a support, cable or foundation, because it is the force the structure must actually carry. Weight is just one particular force, so the general force calculator covers every other case.
Frequently asked questions
- How do I calculate weight?
- Multiply the mass by gravity (9.8): W = m·g.
- What is the difference between mass and weight?
- Mass is the amount of matter in kg; weight is the gravitational force on it in newtons.
- What value of g does this use?
- It uses g = 9.8 m/s², standard gravity near Earth's surface.
- What are the units of weight?
- Newtons (N), the SI unit of force.
- How do I convert newtons back into kilograms or pounds?
- Divide newtons by 9.8 to recover the mass in kilograms — 98 N gives 10 kg. To express the same force in pounds-force, divide the newtons by about 4.448, so 98 N is roughly 22 lbf.