How do you calculate reaction time from a ruler drop?

Take a 15 cm catch. The distance is 0.15 m, twice that divided by 9.80665 is 0.0306, and the square root of that is 0.175 s, or 175 ms. The converter does the same for any catch up to a metre.

How should I read my results?

A shorter catch is a quicker reaction. The time grows with the square root of the distance, so a 5 cm catch is 101 ms and a 20 cm catch is 202 ms: four times the distance, twice the time. Take five drops, use the middle one, and compare it with your own earlier results, since another pair of people will drop and read the ruler differently.

Is this the reaction time test used in fitness testing?

The ruler drop is a standard reaction time test in fitness testing and school PE, and it needs only a ruler and a partner. This page converts the catch distance into a time; it does not grade the result against any fitness table.

Can I use a ruler marked in inches?

Yes. Choose inches and type the mark at your thumb; the chart switches to 2 to 20 inches. A 12-inch ruler covers catches up to about 249 ms.

Does it work as a stick drop test?

Yes. Any straight stick or metre stick falls the same way, so if you can read how far it dropped before you caught it, enter that distance. The converter accepts catches up to 100 cm.

Ruler Drop Reaction Time Test

The ruler drop test needs a partner and a ruler, and this page does the arithmetic. Enter how far the ruler fell before you caught it, in centimetres or inches, and read the time it was falling, which is your reaction time. The steps for the drop and a chart of catch distances sit with the converter.

Ruler drop reaction timeReadyHow far the ruler fell before you caught it

Distance fallen

Ruler marked in

A partner holds the ruler upright with its zero mark level with the top of your open thumb and finger, then lets go without warning. Catch it as fast as you can and read the mark at the top of your thumb: that is the distance it fell. Changing the unit reads the number you typed in the new unit. A ruler that falls past the end of its scale is a miss rather than a time, so drop it again. Five drops and their middle reading tell you more than one.

Ruler drop chart, centimetres
Caught at	Reaction time
5 cm	101 ms
10 cm	143 ms
15 cm	175 ms
20 cm	202 ms
25 cm	226 ms
30 cm	247 ms
35 cm	267 ms
40 cm	286 ms
45 cm	303 ms
50 cm	319 ms

How the time is worked out. A dropped ruler falls freely, so the distance gives the time: t = √(2d / g), with d in metres and g = 9.80665 m/s², standard gravity. Air resistance on a ruler over this distance is far too small to show at a whole millisecond. The answer is only as precise as the mark you read: a centimetre either way moves a 15 cm catch by about 6 ms.

Common questions

How do you calculate reaction time from a ruler drop?: Take a 15 cm catch. The distance is 0.15 m, twice that divided by 9.80665 is 0.0306, and the square root of that is 0.175 s, or 175 ms. The converter does the same for any catch up to a metre.
How should I read my results?: A shorter catch is a quicker reaction. The time grows with the square root of the distance, so a 5 cm catch is 101 ms and a 20 cm catch is 202 ms: four times the distance, twice the time. Take five drops, use the middle one, and compare it with your own earlier results, since another pair of people will drop and read the ruler differently.
Is this the reaction time test used in fitness testing?: The ruler drop is a standard reaction time test in fitness testing and school PE, and it needs only a ruler and a partner. This page converts the catch distance into a time; it does not grade the result against any fitness table.
Can I use a ruler marked in inches?: Yes. Choose inches and type the mark at your thumb; the chart switches to 2 to 20 inches. A 12-inch ruler covers catches up to about 249 ms.
Does it work as a stick drop test?: Yes. Any straight stick or metre stick falls the same way, so if you can read how far it dropped before you caught it, enter that distance. The converter accepts catches up to 100 cm.

Timed with the browser's high-resolution clock, to the millisecond it reports. The figure includes your screen or speaker presenting the signal and your device registering the press, so it is comparable between your own runs on one machine rather than against a laboratory instrument. A ruler drop time is free-fall arithmetic, only as precise as the mark you read at the catch.