Enter crash scenario
- Enter a valid vehicle mass.
- Enter a valid initial speed.
Example data table
These examples show both methods side-by-side using the same inputs.
| Scenario | Mass (kg) | vi (km/h) | vf (km/h) | Duration (s) | Distance (m) | Time avg force (kN) | Distance avg force (kN) | Time g | Distance g | Peak factor |
|---|---|---|---|---|---|---|---|---|---|---|
| Urban stop | 1500 | 60 | 0 | 0.15 | 0.75 | 166.7 | 277.8 | 11.3 | 18.9 | 2.0 |
| Moderate impact | 1200 | 50 | 10 | 0.20 | 1.00 | 66.7 | 111.1 | 5.7 | 9.4 | 1.8 |
| High-speed barrier | 2000 | 80 | 0 | 0.12 | 0.90 | 370.4 | 548.7 | 18.9 | 28.0 | 2.2 |
| Compact crash | 1700 | 40 | 0 | 0.18 | 0.60 | 104.9 | 174.9 | 6.3 | 10.5 | 1.7 |
| Offset collision | 1400 | 90 | 30 | 0.14 | 1.20 | 166.7 | 324.1 | 12.1 | 23.6 | 2.0 |
Formula used
- Time-based (Impulse): F̄ = m·Δv/Δt, where Δv = vi − vf.
- Distance-based (Work–energy): F̄ = ΔKE/d, with ΔKE = ½m(vi2 − vf2).
- Deceleration: a = Δv/Δt (time) or a = (vi2 − vf2)/(2d) (distance).
- g-load: g = a/9.80665.
- Impulse: J = m·Δv.
These are average estimates under simplified assumptions. Peak forces can be higher than averages.
How to use this calculator
- Enter the vehicle mass and select its unit.
- Enter initial and final speeds, then pick a speed unit.
- Select a method: time-based, distance-based, or both.
- Provide duration and/or stopping distance as available.
- Optionally set a peak factor for peak force estimates.
- Click Calculate, then export to CSV or PDF.
For conservative estimates, use shorter durations or smaller distances.
Car crash force guide
1) What this crash force number means
In this calculator, “crash force” is an average impact force during the deceleration pulse. It is not a single instant peak. Average force helps compare scenarios, estimate loads on restraints, and see how mass, speed, time, and crush distance interact. It also shows why similar speeds can create very different outcomes.
2) Two ways to estimate average impact force
The time-based model uses impulse: F̄ = m·Δv/Δt. The distance-based model uses work–energy: F̄ = ΔKE/d. Both assume roughly constant deceleration, so treat outputs as practical estimates and compare both methods when possible. Use time-based when you know pulse duration, and distance-based when you know crush or stopping distance.
3) Example scenario with real numbers
For a 1500 kg vehicle changing from 60 km/h to 0, Δv ≈ 16.67 m/s. If the pulse lasts 0.15 s, deceleration is about 111 m/s² (≈11.3 g) and average force is ≈166.7 kN.
4) Why duration and crush distance change results
If the same event stops over 0.75 m of effective crush, the distance-based average force becomes ≈277.8 kN and deceleration ≈185 m/s² (≈18.9 g). Double the crush distance and the distance-based force halves. Halve the duration and the time-based force doubles. That is why better inputs matter more than extra decimals.
5) Peak factor and force pulse shape
Real crash pulses rise and fall. A peak factor (for example 2.0×) gives a simple peak estimate: a 166.7 kN average becomes ≈333 kN peak. Peak-to-average ratios often sit near 1.5–3. Use this as sensitivity, not certification.
6) Using g-load to sanity check
g-load is a/9.80665. Minor bumps may be below 2 g, while severe crashes can exceed 10 g depending on the pulse and structure. If you see 30–50 g, recheck units and confirm final speed is not higher than initial speed.
7) Practical tips for better inputs
Prefer measured or reconstructed Δv. Many impact pulses fall around 0.08–0.18 s, and 0.5–1.2 m can represent major front-end deformation. Run both methods, document assumptions, and export results for reporting. Large gaps between methods usually mean time or distance needs refinement.
FAQs
1) Which inputs matter the most?
Speed change (Δv) is the biggest driver. After that, impact duration controls the time-based force, and crush or stopping distance controls the distance-based force. Mass scales both methods linearly.
2) Why do the two methods give different forces?
Because you may be assuming a different deceleration pulse shape. A short duration implies a sharp pulse, while a short distance implies rapid energy absorption. If both inputs describe the same crash, results should be closer.
3) What does peak factor do?
Peak factor multiplies the computed average force to estimate a simple peak. Real pulses are not flat, so peaks can be higher than averages. Choose a factor based on test data or sensitivity testing.
4) Can I use mph and pounds?
Yes. Select lb for mass and mph for speed, and the calculator converts to SI internally. Results are shown in Newtons, kilonewtons in the table, and g for deceleration.
5) Why do I see a warning about high g-load?
Very high g values often come from unit mistakes, like entering milliseconds as seconds or centimeters as meters. They can also indicate an unrealistically short pulse or distance for the chosen speed change.
6) Is this suitable for injury prediction?
No. This tool estimates average forces from simplified physics. Injury risk depends on occupant position, restraint systems, crash pulse shape, and biomechanics. Use it for comparison and education, not medical or legal conclusions.