Reaction Speed Test
Measure reaction time to brake lights and calculate braking distance
Features
Measure 5 times with brake lights
Measure reaction to red light and display average and fastest time
Braking distance by speed
Calculate distance table for 30-100 km/h and custom speeds
Switch between km/h and mph
Switch to mph to see distances in feet, readable in international formats
False start detection and personal best
Early taps require retry, and highest average is saved to device
How to Use
Tap the reaction area
Tap the car's rear brake light area once to enter waiting state
Tap when the light turns on
Tap or press spacebar when brake light turns red
Repeat 5 times and check results
See average reaction time, fastest time, rating, and braking distance table
Change speed and unit
Enter custom speed or switch to mph to match your driving
Copy or retry
Copy results to share or tap retry to measure again
Use Cases
Pre-check before license renewal or training
Know your reaction time and braking distance beforehand
Discuss family driving concerns
Measure together with worried family members for data-driven conversation
Check condition before driving
Compare reaction time when tired or sleep-deprived vs. normal state
Reaction speed competition with friends
Take turns measuring to compete on fastest average reaction time
Knowledge
What is braking distance?
Braking distance is the distance a vehicle travels from when the driver becomes aware of danger until the brakes begin to take effect.
- Braking distance：Braking distance is the distance traveled from when brakes engage until the vehicle stops, and varies significantly based on road conditions, tires, and vehicle weight.
- Stopping distance：Stopping distance is the sum of braking distance and reaction distance, representing the total distance from when danger is detected until the vehicle completely stops.
How to calculate braking distance
Braking distance is calculated by multiplying the distance traveled per second by reaction time in seconds.
- In km/h (m)：When speed is in km/h, divide by 3.6 to get meters per second. At 60 km/h with 0.25 second reaction time, the distance is approximately 4.2 m.
- In mph (ft)：When speed is in mph, multiply by approximately 1.467 to get feet per second. At 60 mph with 0.25 second reaction time, the distance is approximately 22.0 ft.
Reaction time guidelines
In screen-based tests where you wait for a cue and tap, reaction times typically range from 0.2 to 0.3 seconds (200-300 ms).
- Reaction time while driving：In actual driving, detecting danger, making decisions, and moving your foot from accelerator to brake takes time, resulting in typical reaction times of 0.75-1 second.
- Conditions that delay reaction：Reaction time increases when tired, drowsy, intoxicated, or distracted by thoughts or phone use, which proportionally increases braking distance.
Safety and Privacy
Runs entirely in your browser
Your input data is processed only within your browser and is never sent externally.
Processing only in your browser
Measuring reaction time and calculating braking distance is processed entirely within your browser, and input data is not sent to any server.
Communications encrypted with HTTPS
Page loading is also encrypted by TLS, and content cannot be read by third parties.
No transmission to third parties
Input content is not sent to external services such as ad networks or trackers.
No automatic saving of results
Reaction time and personal best and input suggestions are not stored on the server.
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Updates
- update #359
Added reaction time test: convert response time to brake lamp into braking distance
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