Calculating Impact Forces

This guide is designed to assist Police Services in quickly calculating impact forces, to assist in investigations.

How to Calculate Impact Forces – Punch

This calculation is to be used when the victim has been punched with a fist.

Weight of Perpetrator (WP) – in kg

Weight of Arm (WA) – in kg (if arm weight unknown, use the average arm weight of 4.5kg)

Arm Length of Perpetrator (ALP) – in cm (if arm length unknown, use the average arm length of 70cm)

The calculation is:

WP x WA x ALP  = Force of Impact (N)

         1000

How to Calculate Impact Forces – Blunt Object

This calculation is to be used when the victim has been struck with a blunt object, such as a brick or metal rod.

Weight of Blunt Object (WB) – in kg

BMI of Perpetrator (BMIP)

Arm Length of Perpetrator (ALP) – in cm (if arm length unknown, use the average arm length of 70cm)

The calculation is:

WB x BMIP x ALP  = Force of Impact (N)

How to Calculate Impact Forces – Stabbing

This calculation is to be used when the victim has been stabbed with a knife or other bladed instrument.

You will need to know:

Weight of Knife (WK) – in kg

BMI of Perpetrator (BMIP)

Weight of Perpetrator (WP) – in kg

The calculation is:

WK x BMIP x WP  = Force of Impact (N)

How to Calculate Impact Forces – Fall

This calculation is to be used when the victim has fallen and struck themselves on an object or the ground.

You will need to know:

Height of Victim (HV) – in cm

Weight of Victim (WV) – in kg

Height of Object Struck (HO) – in cm (this is 0cm if they have hit the ground)

The calculation is:

WV(HV – HO)  =    Force of Impact (N)

     9.807