Reaction time test

Method and sources of error

1. After each start the box is blue, and it turns yellow after a random wait of 1.5 to 4.5 seconds. The time runs from the frame in which yellow is drawn to the moment you press the mouse, touch the screen or press the space bar. It is measured with performance.now() and the time stamp of the input event.
2. A click before the box turns yellow is too early. A response faster than 100 ms is treated as a guess (a rule of this tool). Neither counts, and the try must be repeated.
3. The test has five tries. The result shows the average, median, fastest and slowest times. The median is less affected by a single slip.
4. Sources of error: a 60 Hz screen draws a new frame about every 16.7 ms, so yellow may appear one frame late, and the screen itself adds from a few to several tens of milliseconds. A mouse, keyboard or touch screen also adds from a few to several tens of milliseconds; wireless devices and touch screens are usually slower. Woods and others (2015) measured about 18 ms for their screen and gaming mouse together, and noted that standard mouse drivers may add 20 ms or more. Results for the same person may differ by tens of milliseconds on different devices.
5. Timing is less accurate when the browser tab is in the background or the computer is busy. Please keep this tab in the foreground and close programs that use a lot of resources.

Sources

1. Woods, Wyma, Yund, Herron, Reed (Frontiers in Human Neuroscience, 2015): Factors influencing the latency of simple reaction time

Last checked: 31 October 2026.