Stopping Distance Calculator

Total stopping distance = reaction distance + braking distance. Reaction distance is the distance traveled during the driver's reaction time (typically 1.5 seconds per NHTSA). Braking distance is the distance required for the vehicle to come to a complete stop once the brakes are applied, calculated using the kinematic equation: d = v^2 / (2 x mu x g), where v is speed in m/s, mu is the coefficient of friction, and g is gravitational acceleration (9.81 m/s^2).

NHTSA and SAE research cite typical friction coefficients of 0.7 to 0.8 for dry asphalt, 0.4 to 0.5 for wet asphalt, 0.2 to 0.3 for packed snow, and 0.05 to 0.10 for ice. ABS brakes allow braking at near-maximum friction. Without ABS, wheel lock reduces the effective friction coefficient. This calculator uses user-editable friction values so you can model different conditions.

Braking distance increases with the square of speed. If you double your speed from 30 mph to 60 mph, braking distance quadruples (not doubles). This is why speed limits in school zones and residential areas are critical. At 60 mph on dry pavement, total stopping distance is approximately 240 to 300 feet. At 30 mph it is approximately 75 to 100 feet.

AASHTO (American Association of State Highway and Transportation Officials) uses 2.5 seconds as the design reaction time for highway geometric design (AASHTO Green Book). NHTSA uses 1.5 seconds for typical braking scenarios. This calculator allows you to enter your own reaction time; 1.5 to 2.5 seconds covers the realistic range for most drivers.

For the same tire-road friction coefficient, vehicle weight does not significantly affect stopping distance in theory because both the braking force and inertia scale with weight. However, heavier vehicles with the same brakes and tire contact area actually stop in longer distances because brake systems and tires have limits. NHTSA testing shows that large SUVs and trucks often require 20 to 40% more stopping distance than smaller passenger cars.