Ruler drop test
The classic science-class reaction test, on screen. A ruler hangs between your fingers and drops without warning: catch it as fast as you can. The shorter the distance, the faster your reaction.
Three drops, then you get your average catch distance. Shorter is faster.
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How the online ruler drop works
Tap to hold the ruler. After a random pause it starts to fall, speeding up exactly like a real object in free fall. Click, tap or press Space to catch it. We read where your fingers are on the ruler, just like in class.
You get three drops, and your average catch distance is your score. Shorter is better.
The physics: from centimetres to milliseconds
A falling object travels d = ½ × g × t², where g is about 9.81 m/s². So the distance tells us the time: t = √(2d ÷ g). A catch at 20 cm means about 202 ms; 10 cm means about 143 ms; 30 cm means about 247 ms.
Because the ruler speeds up while it falls, a small difference in time makes a big difference in distance near the bottom of the ruler.
Did the test with a real ruler?
Use the calculator below the ruler: enter the distance where you caught it and press “Work out my reaction time”. It uses the same formula, so it's great for school experiments and lab reports.
For a fair real-life test, the catcher's thumb and finger start level with 0 cm, open but not touching the ruler, and the person dropping it doesn't give any signal.
Questions & answers
What is a good ruler drop result?
Around 15 to 25 cm is typical (about 175 to 225 ms). Under 15 cm is fast.
Why 50 cm?
A school ruler is usually 30 cm, which slower catches can miss completely. The longer on-screen ruler means fewer misses.
Is the on-screen ruler exactly like a real one?
The falling motion follows real physics, but you react to a picture with a mouse or screen, which adds a little delay compared to catching with your hand.
What does a miss mean?
The ruler fell more than 50 cm, which takes about 320 ms. Try again and stay focused.