Force Calculator
Newton's second law solved for force, mass or acceleration, plus weight on any planet from NASA surface gravities — in newtons, pounds-force and kgf.
Force Calculator: with the default inputs, force (n) is 30.
Not used when solving for mass.
Not used when solving for acceleration or weight.
Used when solving for mass or acceleration.
- Solved for
- F = 30 N
- Force (lbf)
- 6.7443
- Force (kgf)
- 3.0591Kilogram-force: the weight of 1 kg under standard gravity.
- Mass
- 10 kg
- Acceleration (m/s²)
- 3
- Acceleration in g's
- 0.3059Acceleration ÷ 9.80665 m/s².
Assumptions
- Constant mass and non-relativistic speeds.
- Planetary g values are equatorial surface gravities from NASA; Earth uses standard g₀ = 9.80665 m/s².
- Force and acceleration are along the same line (1-D).
| Body | g (m/s²) | Weight (N) | Weight (lbf) |
|---|---|---|---|
| Earth | 9.81 | 98.07 | 22.05 |
| Moon | 1.62 | 16.2 | 3.64 |
| Mars | 3.71 | 37.1 | 8.34 |
| Mercury | 3.7 | 37 | 8.32 |
| Venus | 8.87 | 88.7 | 19.94 |
| Jupiter | 24.79 | 247.9 | 55.73 |
| Saturn | 10.44 | 104.4 | 23.47 |
| Uranus | 8.87 | 88.7 | 19.94 |
| Neptune | 11.15 | 111.5 | 25.07 |
| Pluto | 0.62 | 6.2 | 1.39 |
| Sun | 274 | 2,740 | 615.98 |
Surface gravities from the NASA Planetary Fact Sheet (equatorial). Earth uses the standard g₀ = 9.80665 m/s²; the fact-sheet value is 9.80.
How this is worked out
The formula
F = m × a (Newton's second law) W = m × g (weight) F = net force (N = kg·m/s²) m = mass (kg) a = acceleration (m/s²) g = 9.80665 m/s² on Earth (standard) 1 lbf = 4.44822 N 1 kgf = 9.80665 N
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Solve for
- Choose one of 4 options.Force — from mass & acceleration (F = ma) · Mass — from force & acceleration · Acceleration — from force & mass · Weight — on a planet or moon
- Mass
- Not used when solving for mass.in kg · 0 or more · defaults to 10
- Acceleration
- Not used when solving for acceleration or weight.defaults to 3
- Force
- Used when solving for mass or acceleration.defaults to 30
- Planet or moon (weight mode)
- Choose one of 11 options.Earth — g = 9.80665 m/s² · Moon — g = 1.62 m/s² · Mars — g = 3.71 m/s² · Mercury — g = 3.7 m/s² · Venus — g = 8.87 m/s² · Jupiter — g = 24.79 m/s² · Saturn — g = 10.44 m/s² · Uranus — g = 8.87 m/s² · Neptune — g = 11.15 m/s² · Pluto — g = 0.62 m/s² · Sun — g = 274 m/s²
What you get back
- Force (N)main answer
- Solved for
- Force (lbf)
- Force (kgf)
- Kilogram-force: the weight of 1 kg under standard gravity.
- Mass
- Acceleration (m/s²)
- Acceleration in g's
- Acceleration ÷ 9.80665 m/s².
What this assumes
- Constant mass and non-relativistic speeds.
- Planetary g values are equatorial surface gravities from NASA; Earth uses standard g₀ = 9.80665 m/s².
- Force and acceleration are along the same line (1-D).
About this calculator
Newton's second law, F = ma, is the whole of introductory mechanics in three letters: the net force on an object equals its mass times the acceleration it produces. Weight is the special case where the force is gravity and the acceleration is g. Choose what to solve for, enter the other two, and the calculator shows the rearranged equation with your values, converts to pounds-force and kilograms-force, and — in weight mode — shows what the same mass weighs on every planet.
Mass is not weight
Your mass is the same everywhere; your weight is the force gravity exerts on it, and it changes with g. A 70 kg person weighs 686 N on Earth, 113 N on the Moon and 1,735 N on Jupiter — the table under the results lists all of them. Bathroom scales are calibrated to display mass by assuming Earth gravity, which is why a scale on the Moon would read 11.6 "kg" for that person.
Reading the results
- Newtons are the SI unit: 1 N accelerates 1 kg at 1 m/s². An apple weighs about 1 N.
- Pounds-force are what US engineering uses; 1 lbf = 4.44822 N exactly, the weight of one pound-mass under standard gravity.
- Kilograms-force (kgf, kp) still appear on old gauges and torque specs: 1 kgf = 9.80665 N.
- Acceleration in g's — useful for crash and roller-coaster numbers; sustained 5 g is a fighter-pilot load.
Common mistakes
- Using the wrong force. F in F = ma is the net force — the vector sum of everything acting. A book at rest on a table has gravity and the table's push cancelling to zero net force and zero acceleration.
- Mixing pounds. "Pounds" can be mass (lbm) or force (lbf). Under Earth gravity 1 lbm weighs 1 lbf, which hides the difference until you leave Earth or do a dynamics problem.
- Using g = 10 in exam calculations when the marking expects 9.8, or vice versa. This calculator uses the standard 9.80665.
Where it breaks
F = ma assumes constant mass and speeds far below light. A rocket burning fuel needs the momentum form F = dp/dt, and relativistic objects need γ factors. Rotating things obey the rotational analogue τ = Iα. Surface gravity also varies by about 0.5% across Earth (equator vs. poles, altitude), so "9.81" is a rounding, not a law.
Frequently asked questions
▸What is the formula for force?
F = ma: net force equals mass times acceleration. With mass in kilograms and acceleration in m/s², the force is in newtons.
▸How do I calculate weight from mass?
Multiply by the local gravitational acceleration: W = mg. On Earth g = 9.80665 m/s², so 1 kg weighs 9.81 N (2.205 lbf).
▸How much would I weigh on Mars?
About 38% of your Earth weight, because Mars's surface gravity is 3.71 m/s² versus Earth's 9.81. Your mass would be unchanged.
▸How do I convert newtons to pounds?
Divide by 4.44822 to get pounds-force (lbf). 100 N ≈ 22.5 lbf. To get pounds-mass you would instead divide the weight by g and convert kilograms.
▸Why is the net force zero for an object at rest?
Because its acceleration is zero, and F = ma says zero acceleration means zero net force. Forces are still acting — gravity down, the floor up — they simply cancel.
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