Force Calculator
Newtons, pounds force, and g force from mass times acceleration.
What it does
Newton second law says force equals mass times acceleration. Push twice the mass or accelerate twice as hard and the force doubles; it is the most direct equation in mechanics.
The tool above takes mass and acceleration in metric or imperial. It returns newtons first with pounds force beside them, plus the acceleration stated in g units for feel.
The default of 5 kg at 5 m/s² gives 25.0 N, about 5.6 lbf or 0.51 g. The imperial mirror of 11.02 lb at 16.4 ft/s² lands on the same 25.0 N through converted units.
The newton definition follows NIST SI unit references (one kilo meter per second squared) with the same F = ma treatment in Khan Academy physics units. Weight falls out as the special case with acceleration set to local gravity.
How to use
- Pick metric or imperial for your numbers.
- Enter the mass in kg or lb.
- Enter the acceleration in m/s² or ft/s².
- Read newtons first for the SI answer.
- Use lbf and g force for shop and body feel.
Formula
- mass
- Kilos or converted pounds being pushed.
- acceleration
- Rate of velocity change per second.
- g
- 9.80665 m/s² reference dividing acceleration for g force.
Direction is ignored here; the magnitude follows mass times acceleration regardless of heading. Friction and other forces add as separate vectors outside this page.
Worked example
Example: 5 kg at 5 m/s²
Metric defaults: 5 kg, 5 m/s².
- Multiply: 5 x 5 = 25 N.
- Pounds force: 25 x 0.224809 = 5.6 lbf.
- g force: 5 / 9.80665 = 0.51 g.
- Weight check: 5 kg weighs 5 x 9.81 = 49 N, about double this push.
- Tool shows 25.0 N, 5.6 lbf, 0.51 g.
Reference table
| Acceleration | Force | g force |
|---|---|---|
| 1 m/s² | 5.0 N | 0.10 g |
| 5 m/s² | 25.0 N | 0.51 g |
| 9.81 m/s² | 49.1 N | 1.00 g |
Limits
- Net force only; friction and thrust add separately.
- Constant mass assumed; rockets lose mass as they burn.
- Classical range; extreme speeds need relativity.
- Direction ignored, magnitude only.
Common mistakes
- Weighing in pounds mass and calling it force directly.
- Mixing grams with kilos without converting.
- Reading g force as grams of mass.
- Forgetting gravity when pushing uphill.
- Adding forces pointing different ways as plain numbers.
Try it yourself
Quick checks. Answers sit tucked under each question.
10 kg at 2 m/s²?
20.0 N, about 4.5 lbf.
1 kg at 9.81 m/s²?
9.8 N, exactly 1.00 g by definition.
Zero acceleration?
0 N at any mass: no change in motion needs no net force.
Questions
What is one newton?
The force pushing 1 kg at 1 m/s². A 5 kg push at 5 m/s² is 25 N.
Newtons or pounds force?
Same push in SI vs imperial: multiply newtons by 0.224809 for lbf.
What is g force?
Acceleration divided by 9.81. Here 5 m/s² reads 0.51 g.
Is weight a force?
Yes: mass times gravity. 5 kg weighs about 49 N on Earth.
Why lb vs lbf?
Pounds mass weigh pounds; force pounds push. On Earth 1 lb mass weighs about 1 lbf.
Net vs applied force?
Applied minus friction and drag gives net, and only net accelerates the mass.