Impact Force Calculator
The force of an impact from the fall height and the stopping distance — with the g-force and how much a softer surface would help.
How hard something hits.
How the impact force calculator works
Impact force is not fixed by the fall; it is set by how far the object travels while stopping. Energy mgh must be absorbed over distance d, so F = mgh/d.
That is why the stopping distance is the only variable worth engineering. A 2 m fall onto concrete stopping in 5 mm generates 400 times the falling object's weight; the same fall onto 200 mm of crash matting generates ten times less.
Formula: F = m g h / d; v = √(2gh)
Worked examples
| Inputs | Average impact force | Note |
|---|---|---|
| 80 kg falling 2 m, stopping in 50 mm | 31,381 N | 31.4 kN — 40 g |
| Onto concrete, 5 mm | 313,813 N | ten times worse |
| Onto 300 mm of matting | 5,230 N | 5.2 kN — survivable |
FAQFrequently asked questions
Why is the stopping distance the key variable?
Because the energy is fixed by the fall. All that changes is the distance over which it is absorbed, and force is energy divided by that distance.
How much does soft ground help?
Enormously. Stopping in 200 mm rather than 5 mm cuts the force by a factor of forty.
Is this an average or a peak force?
An average. Real peak forces are typically 1.5 to 3 times higher, because deceleration is not uniform.
What fall is survivable?
It depends far more on the surface than the height. Falls from over 20 m have been survived onto snow or water; 2 m onto concrete has killed people head-first.
Does this apply to car crashes?
The same principle. A crumple zone is a stopping distance, and every extra centimetre of it lowers the force on the occupants.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G, g₀, R, c
- NIST Special Publication 811 — Guide for the use of the International System of Units — unit conversions
- The Engineering ToolBox — material properties — specific heats, expansion coefficients, densities
- National Measurement Institute — Australia's measurement authority
Last checked: September 2026. Constants are the CODATA 2018 values; formulas are the standard textbook forms.