How to Do the Ruler Drop Test
You need a 30 cm ruler, a partner and a table.
Get in position
Rest your forearm on a table with your hand past the edge. Hold your thumb and finger a few cm apart at the zero mark.
Partner drops it
Your partner holds the top and lets go without warning. They should change the wait on every try.
Catch and read
Catch it as fast as you can and read the mark just above your thumb.
Enter it here
Type the number and press Add catch. Repeat 5 to 10 times and use your average.
Ruler Drop Conversion Chart and Ratings
Values are rounded to the nearest millisecond, using gravity of 9.81 m/s².
Most people catch the ruler between 15 and 25 cm. The ratings are a VoltReflex guide for fun and classroom use, not a scientific standard.
Ruler Drop vs Online Reaction Test
Two good tools that measure slightly different things.
The physics
A dropped ruler speeds up as it falls, so distance tells you time. That is why 10 cm is not twice as fast as 20 cm. Our ruler drop test guide explains the formula.
Online test
The reaction time test adds screen and mouse delay, so scores are usually higher than ruler scores. Compare like with like.
For students
Planning a class or science fair project? See our reaction time experiment for students with method and results table.
Go further
Try the audio test to react to sound, or the choice reaction test to add a decision.
Frequently Asked Questions
Quick answers about the ruler drop calculator.
How do you calculate reaction time from a ruler drop?
Use the falling object formula. Reaction time equals the square root of 2 times the distance divided by 9.81, with the distance in metres. A catch at 20 cm, or 0.2 m, works out to about 202 ms. This calculator does the maths for you.
What is a good ruler drop score?
Most people catch a 30 cm ruler somewhere between 15 and 25 cm, which is roughly 175 to 226 ms. Under 15 cm is quick. If you miss a 30 cm ruler, that try took longer than about 247 ms.
Can I enter inches instead of centimetres?
Yes. Switch the unit to inches and type the mark above your thumb. The calculator converts inches to centimetres, 1 inch is 2.54 cm, and then works out your reaction time.
Why is my ruler score faster than my online test?
The ruler only measures your body. An online test also includes the time your screen takes to change and the time your mouse, keyboard or touchscreen takes to register. Compare ruler with ruler and online with online.
How many catches should I do?
Do at least 5 and ideally 10 catches, then use the average. Single catches jump around a lot. Ask your partner to change the waiting time on every drop so you cannot guess the moment.
VoltReflex results are for entertainment and self-benchmarking, not a medical diagnosis. Method based on the IIHS Think Fast, Act Fast classroom activity and NRICH, How Do You React