Estimate the average force when a moving or falling object stops. Enter the mass, the drop height or impact speed, and how far or how long it takes to stop. You get the force in newtons, pounds-force and kilograms-force, the g-force, the energy absorbed, and a table showing how much padding reduces the force.
Last updated:
Object
Speed at impact from
How it stops
Stopping given as
How far it travels while slowing down: padding squash, crumple zone, bent knees
Enter your values to see the result.
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How to use the Impact Force Calculator
Enter the mass of the object and pick its unit.
Choose drop height or impact speed and enter the value.
Enter how it stops: the stopping distance (how far it squashes or slides) or the stopping time.
Read the average force, g-force and energy.
Check the table to see how a longer stopping distance lowers the force.
Impact force formulas
Speed after a fall: v = √(2gh), with g = 9.80665 m/s² (air resistance ignored).
Kinetic energy: KE = ½mv².
From stopping distance (work-energy): F = ½mv² ÷ d.
From stopping time (impulse-momentum): F = mv ÷ t.
Converting between them (constant deceleration): d = v × t ÷ 2. G-force: a ÷ g = F ÷ (m × g).
Worked example: an egg (60 g) falls 2 m onto 5 cm of padding. Speed v = √(2 × 9.81 × 2) = 6.26 m/s, energy = ½ × 0.06 × 6.26² = 1.18 J, force = 1.18 ÷ 0.05 = 23.5 N, about 40 g. On a hard floor with 2 mm of give, the same egg would feel about 588 N, 25 times more.
Free-fall speed and energy reference
Speed reached after a fall (no air resistance) and the energy of a 1 kg object:
Drop height
Impact speed
Speed (mph)
Energy for 1 kg
Force for 1 kg stopped in 1 cm
0.5 m (1.6 ft)
3.13 m/s
7.0
4.9 J
490 N
1 m (3.3 ft)
4.43 m/s
9.9
9.8 J
981 N
2 m (6.6 ft)
6.26 m/s
14.0
19.6 J
1,961 N
5 m (16.4 ft)
9.90 m/s
22.2
49.0 J
4,903 N
10 m (32.8 ft)
14.0 m/s
31.3
98.1 J
9,807 N
Ways to reduce impact force
Increase the stopping distance: foam, springs, crumple zones and soft landing surfaces spread the stop over more distance.
Increase the stopping time: airbags and padded packaging slow the object over more milliseconds.
Reduce the speed: energy grows with the square of speed, so halving the speed cuts the energy to a quarter.
Spread the force: a larger contact area lowers pressure even when the total force is the same.
Frequently asked questions
How do you calculate impact force?
Impact force depends on how quickly the object stops. With a stopping distance d, the average force is F = ½mv² ÷ d (the kinetic energy divided by the distance). With a stopping time t, F = mv ÷ t (momentum divided by time). The speed after a fall from height h is v = √(2gh).
What is the impact force of a falling object?
It depends on the stopping distance as much as the height. A 2 kg object dropped 1.5 m reaches 5.42 m/s and has 29.4 J of energy. If it stops in 2 cm, the average force is 29.4 ÷ 0.02 ≈ 1,470 N (about 330 lbf); on a 10 cm cushion it is only about 294 N.
Why can't I calculate impact force from mass and height alone?
Because the force depends on how the object stops. The same fall produces a huge force on concrete (a stop of a millimeter or two) and a small force on a foam pad (several centimeters). Mass and height give the energy and speed, but you also need the stopping distance or time.
How is g-force related to impact force?
The g-force is the deceleration divided by standard gravity (9.80665 m/s²). It also equals the average impact force divided by the object's weight, so an impact of 20 g means the stopping force is 20 times what the object weighs.
Is the result the peak force?
No, it is the average force over the stop, assuming steady deceleration. Real impacts usually build up and fall off, so the peak can be noticeably higher than the average, which is why engineers measure impacts with sensors when it matters.
How do padding and crumple zones reduce impact force?
They increase the stopping distance and time. Since force equals energy divided by stopping distance, doubling the distance halves the average force. That is the idea behind helmets, airbags, crash mats, packaging foam and bending your knees when you land.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.