Car Crash Calculator

The average impact force is calculated using the conservation of energy: F = mv² / (2d), where m is mass, v is velocity, and d is the collision distance (crumple zone). This gives the average force exerted on an object during deceleration from full speed to a complete stop.

G-force is the ratio of impact force to the person's weight force (mass × 9.81 m/s²). It tells you how many times the force of gravity you experience during the crash. A crash at 60 km/h with a 1 m stopping distance produces roughly 14 g — equivalent to having 14 times your body weight pressing on you.

A seat belt extends your effective stopping distance by allowing your body to decelerate with the car rather than continuing forward and hitting the dashboard or windshield. Since impact force is inversely proportional to stopping distance (F = mv²/2d), increasing d significantly reduces the force on your body. Without a seat belt, your stopping distance might be just a few centimeters, multiplying the force dramatically.

Airbags work on the same principle as seat belts — they increase the stopping distance for your head and upper body. By spreading the deceleration over a longer time and distance, airbags reduce peak impact force on the skull and face. Together with seat belts, they form the primary passive safety system in modern vehicles.

There is no single fatal speed threshold — it depends heavily on stopping distance, crash type, and safety equipment. However, research suggests that crashes at or above 60–70 km/h (37–43 mph) without restraints generate g-forces well above the human tolerance limit of approximately 50 g, making serious injury or death increasingly likely. With modern crumple zones and restraints, survivability extends to much higher speeds.

At 100 km/h with a 75 kg person and a 1 m collision distance, the impact force on the body is approximately 28,900 N — generating about 39 g of deceleration. This highlights why high-speed crashes are so dangerous even with safety equipment.

Stopping time is calculated as t = 2d / v, where d is the collision distance and v is the initial velocity in m/s. For example, a crash at 60 km/h (16.67 m/s) with a 1 m crumple zone results in a stopping time of about 120 milliseconds — a fraction of a second that determines survival.

Modern cars are designed with crumple zones typically ranging from 0.5 m to 2 m. In a frontal collision, the car body absorbs energy over this distance. Wearing a seat belt can add an additional 20–30 cm of effective stopping distance for the occupant. Older or smaller vehicles may have significantly shorter crumple zones, increasing crash forces.