How this calculator works
Impulse is the change in momentum, and average force is impulse divided by the time over which it acts. A 75 kg body moving at 10 m/s that stops in 0.05 s implies a momentum change of 750 kg m/s and an average force of 15,000 N. Dividing by the contact area turns the force into pressure. The whole-body mass overstates the effective mass of a punch, because the legs, torso and other arm do not stop with the fist, so use the result as an order-of-magnitude estimate rather than a measurement.
Formula
Impulse = mass x speed. Average force = mass x speed / delivery time. Pressure = force / contact area. Punch speed = force x delivery time / mass. Delivery time = mass x speed / force. Kinetic energy = 0.5 x mass x speed squared.
Worked example
A 75 kg striker with a fist moving at 10 m/s and a 0.05 s stop: impulse is 750 N s, average force is 750 / 0.05 = 15,000 N, and pressure over 0.01 square metres is 1,500 kPa. The kinetic energy is 0.5 x 75 x 100 = 3,750 J, though much of that energy goes into the body and not the target.
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Frequently asked questions
Is this a real punch force?
It is an upper-bound estimate. Force plates and instrumented bags measure the actual force, and elite punches are often in the low thousands of newtons rather than tens of thousands. The difference comes from the effective mass and the short contact time.
Why does delivery time matter so much?
Force is impulse divided by time. Halving the stopping time doubles the average force for the same change in momentum, which is why a hard surface and a stiff strike produce a higher peak force than a padded one.
What is contact area?
It is the area of the fist or glove that meets the target. A smaller area raises pressure for the same force, which is why a bare knuckle concentrates more pressure than a padded glove.