Ruler Drop Test

What is the ruler drop test?

The ruler drop test is a reaction time test: someone lets go of a ruler without warning, you pinch it as fast as you can, and the distance it fell tells you how long you took. This page runs the same test on screen.

• A 1 m ruler hangs with its 0 cm end between your fingers. After a random wait of 1.5 to 5 seconds it falls.
• Your time runs from the animation frame in which the ruler starts to move until your tap, click or space bar press, in whole milliseconds.
• The catch distance in centimetres comes from that time with the free-fall formula, so "Caught at 23 cm, 217 ms" means the same thing on any screen size.
• A grab before the drop counts as grabbed too early, and a ruler that falls its full 1 m (about 452 ms) counts as missed. Neither one is scored, and that drop is repeated.
• A set is five valid catches. Your score is the mean of the middle three, shown in ms and cm.

How is the catch distance worked out?

The catch distance is the distance a dropped object falls in your reaction time: d = ½ × g × t², with g = 9.81 m/s² and t in seconds. Here is a catch of 217 ms worked through.

1. Convert the time to seconds: 217 ms = 0.217 s.
2. Square it: 0.217 × 0.217 = 0.047089.
3. Multiply by g and halve: 0.5 × 9.81 × 0.047089 = 0.231 m.
4. Round to whole centimetres: 23 cm. The screen shows "Caught at 23 cm, 217 ms".

The same formula runs backwards for a real ruler, where you read the distance first: t = √(2d ÷ g). For 23 cm that is √(0.46 ÷ 9.81) = 0.2165 s, or 217 ms. Topend Sports gives this formula with g = 9.8 m/s², which changes these results by far less than 1 cm.

Ruler drop chart: centimetres to milliseconds

The ruler drop chart below converts a catch distance into a reaction time. Every row is computed from t = √(2d ÷ g) with g = 9.81 m/s², rounded to whole milliseconds.

Notice how uneven the steps are. The first 5 cm take about 101 ms, while the last 10 cm, from 90 to 100 cm, take only about 23 ms. That is why a small gain in reaction time saves many centimetres on a slow catch.

Why does a dropped ruler start so slowly?

A dropped ruler starts at rest and gains speed the whole way down, so the distance grows with the square of the time. The curve shows the fall for the full 452 ms it takes to pass 1 m.

How is a set of five scored?

A set score is the mean of your three middle catches, so your fastest and slowest catches are left out. For catches of 250, 230, 270, 240 and 260 ms, the 230 and 270 are dropped and the score is (250 + 240 + 260) ÷ 3 = 250 ms, which is 31 cm on the ruler.

Early grabs and missed drops never enter the set. Only real catches count, so every set ends with five of them.

Your last 10 sets

How do you do the ruler drop test with a real ruler?

The real ruler drop test needs two people and a ruler. These steps combine the coaching protocol from Topend Sports and the classroom lesson from the NSW Department of Education.

1. Rest your forearm on a table with your hand over the edge. Topend Sports uses a 1 m ruler or a yardstick; the NSW lesson uses a 30 cm ruler.
2. Your partner holds the ruler upright with the 0 cm mark level with your open thumb and finger.
3. Your partner lets go without warning, and you pinch the ruler as quickly as you can.
4. Read the distance on the ruler where your thumb caught it. That is the distance it fell.
5. Repeat. The NSW lesson does five drops; Topend Sports suggests 5 to 10, leaving out the highest and lowest.
6. Turn each distance into a time with the chart above.

Topend Sports also publishes rating bands for the real ruler test. This page does not rate your screen score against them, because a screen and an input device add delay that a real ruler does not have.

How do you get a fair ruler drop result?

• Play on one device and one browser when you compare sets. Displays, touch screens and mice each add their own lag, and the amount differs from one device to the next.
• Watch the ruler, not the words. The text does not change when the ruler drops, so the movement is your only cue.
• Do two or three sets before you judge a change. In a 2024 study in Aging Clinical and Experimental Research, the simple ruler drop test gave an ICC of 0.57 between two sessions a week apart, which the authors call poor reliability; the choice version reached 0.81. Single sets wobble.
• Expect slower numbers than in click-on-a-flash tests. A falling ruler moves only a few pixels in its first frames, so the start of the drop is harder to spot than a sudden flash.

Questions