Reaction Time Estimator Formula

Understand the math behind the reaction time estimator. Each variable explained with a worked example.

Use the Reaction Time Estimator

Formulas Used

Reaction Time

reaction_time_ms = round(sqrt(2 * drop_distance_cm / 100 / 9.81) * 1000)

Reaction Time (sec)

reaction_time_sec = round(sqrt(2 * drop_distance_cm / 100 / 9.81) * 1000) / 1000

Performance Rating (lower = better)

rating = round(sqrt(2 * drop_distance_cm / 100 / 9.81) * 1000)

Variables

VariableDescriptionDefault
drop_distance_cmRuler Drop Distance(cm)15

How It Works

How the Ruler Drop Test Works

Formula

Reaction Time = sqrt(2 x Distance / g)

Where distance is in meters and g = 9.81 m/s^2. The result is in seconds; multiply by 1000 for milliseconds.

How to Perform the Test

1. Have a partner hold a ruler vertically at the 0 cm mark between your open thumb and finger. 2. Without warning, the partner drops the ruler. 3. Catch it as quickly as possible and read the cm mark where you caught it.

Benchmarks

| Reaction Time | Rating | |--------------|--------| | < 150 ms | Excellent | | 150-200 ms | Good | | 200-250 ms | Average | | 250-300 ms | Below average | | > 300 ms | Slow |

Worked Example

The ruler fell 15 cm before being caught.

drop_distance_cm = 15
  1. 01Distance in meters = 15 / 100 = 0.15 m.
  2. 02Reaction time = sqrt(2 x 0.15 / 9.81) = sqrt(0.0306) = 0.175 sec.
  3. 03In milliseconds = 175 ms.
  4. 04Rating: Good (150-200 ms range).

Ready to run the numbers?

Open Reaction Time Estimator