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Calculate your reaction time with Omni! With this simple tool, you will learn how to find the average reaction time of a human (you!) using a simple ruler! Keep reading to learn:

  • What is the reaction time: definition and explanation.
  • How to calculate the reaction time: the ruler drop experiment.
  • How to use our calculator for the average reaction time.

And much more: quick! Let's go!

Reaction time definition: what is the reaction time?

The reaction time measures the quickness with which a human, animal, or any other organism reacts to a stimulus of a specific kind.

The reaction time is tightly connected with how the perception of a stimulus gets elaborated by a living being: we can start from simple chemical responses to arrive at the complex operation of the nervous systems of vertebrates. The generic process that defines the reaction time, however, is the same for all levels of complexities:

  1. A stimulus activates a receptor (a sensor dedicated to that specific stimulus).
  2. The receptor elaborates the strength of the stimulus, possibly integrating it over time.
  3. The receptor sends a signal to the effector; any agent that is supposed to control the response.
  4. The response is any mechanical or cognitive action taken as a consequence of the events we listed above.

In vertebrates, this process is managed by our sensory and nervous system, and ends with any part of the body dedicated to the response. In this case, the agents of the process are:

  • The stimulus (this time, it is the same as the general one). Vertebrates can react to a broad spectrum of stimuli: visual ones (if eyes are included in the package), chemical (bad smells are prime examples of a stimulus we react quickly to), mechanical (ever stepped by mistake on your cat's tail, just to find your leg mangled in less than a second?).

  • The receptor is often a sensory neuron, a nerve cell dedicated to the reception of a specific stimulus. Your body is filled with them: from rods and cones in your retina to neurons that terminate with thermoreceptors that suggest to your body when something is too hot (or cold). The sensory neuron also performs the integration, if necessary.

  • The information (usually a spike in electric potential) travels from the neuron — which is often located on the periphery of your body, as our skin is our largest interface with the world of stimuli surrounding us — to the spinal cord. At this point, there are two possible paths:

    • The spinal cord takes full responsibility. In this case, we move directly to the next step (the reaction).

    • The spinal cord relays the signal to the brain (or whatever agglomerate of neurons dedicated to cognitive abilities).

  • In both cases above, an adequate response gets calculated. In the case of the brain, the response travels back to the spinal cord. The spinal cord then sends the response to the proper body part.

🙋 Did you know that the shortest reaction time in the animal kingdom belongs to the star-nosed mole, a small, blind mole from North America: if you present one of these critters with potential food, the decision "eat or not eat" is done in 8 milliseconds by the brain. The moles then complete the feeding action in, on average, about 225 milliseconds, almost the same time a human usually reacts to a visual stimulus.

How to calculate the reaction time: the ruler drop experiment

If you want to calculate your reaction time, use a simple experiment: the results will surprise you! Here we will explain everything you need to know to calculate the reaction time with the ruler drop method.

All you need is the following:

  • A straight ruler with marks; and
  • A friend.

To set up the experiment, follow these steps:

  1. Take the friend, and ask him to hold the ruler by one end. The ruler should be vertical, with the 00 value at the bottom.
  2. Hold your arm still; maybe rest it on a table. Separate your thumb and index finger by about 8 centimeters, and align the center of your fingers with the zero mark on the ruler.

Now it's time for the execution:

  1. The friend releases the ruler without notice.
  2. Close your fingers on the ruler as fast as you can.
  3. Note the length at which your fingers closed on the ruler.

How to calculate the reaction time from this length? We will use a bit of physics!

The ruler, for a brief period of time, is in freefall which means it's moving only under the effect of gravitational force. This allows us to calculate the reaction time using the equations of a uniformly accelerated motion. In particular, we are interested in the equation that gives us the time as a function of the distance:

t=2dgt = \sqrt{\frac{2\cdot d}{g}}

where, in the case of our experiment:

  • ttReaction time;
  • ddDistance at which you stopped the ruler; and
  • ggAcceleration due to gravity. A value of g=9.81 m/s2g = 9.81\ \mathrm{m/s^2} is adequate for most calculations.

🙋 This equation is the same one we used in our free fall calculator. As the drop will be very short and at low speeds, we can ignore the physics we explained at the free fall with air resistance calculator.

Repeat the experiment as many times as you want to calculate the average reaction time: sum all the resulting times and divide the result by the number of attempts.

🙋 Snakes are notoriously fast as lightning: a strike of a danger noodle can cover a foot in 70 milliseconds. Do you know what is faster than a snake? Cats! Our feline friends have average reaction times between 20 and 70 milliseconds. Check this amazing video to see how fast our dorky friends can be.

A cat slapping the aggressiveness out of a snake's snout in less than a tenth of a secon.
Cats' reflexes are unbelievably fast!

How to calculate the average reaction time: an example

Let's say that you collected the following set of data for your two friends, Sammy and Olga:





26 cm26\ \mathrm{cm}

17 cm17\ \mathrm{cm}


28 cm28\ \mathrm{cm}

20 cm20\ \mathrm{cm}


23 cm23\ \mathrm{cm}

16 cm16\ \mathrm{cm}


26 cm26\ \mathrm{cm}

15 cm15\ \mathrm{cm}


25 cm25\ \mathrm{cm}

21 cm21\ \mathrm{cm}

Let's apply the formula for the reaction time to calculate the ruler drop time. Let's fit the values in a similar table:





230.23 ms230.23\ \mathrm{ms}

186.17 ms186.17\ \mathrm{ms}


238.9 ms238.9\ \mathrm{ms}

201.93 ms201.93\ \mathrm{ms}


216.54 ms216.54\ \mathrm{ms}

180.6 ms180.6\ \mathrm{ms}


230.23 ms230.23\ \mathrm{ms}

174.87 ms174.87\ \mathrm{ms}


225.76 ms225.76\ \mathrm{ms}

206.9 ms206.9\ \mathrm{ms}

Find the average reaction time by summing all the values for Sam and Olga and dividing the results by 55 (the number of attempts). For Sam, we find:

tˉr=(230.23+238.9+216.54+230.23+225.76)15=1141.665=228.34 ms\begin{split} \bar{t}_\mathrm{r}&= (230.23+238.9+216.54\\ &\quad+230.23+225.76)\cdot\frac{1}{5}\\[1em] &=\frac{1141.66}{5} = 228.34\ \mathrm{ms} \end{split}

Accounting for the relative roughness of this experiment, we round to 230 ms230\ \mathrm{ms} according to the number of significant figures of the ruler data.

For Olga, we calculate the following:

tˉr=(186.17+201.93+180.6+174.87+206.9)15=950.475=190.1 ms\begin{split} \bar{t}_\mathrm{r}&= (186.17+201.93+180.6\\ &\quad +174.87+206.9)\cdot\frac{1}{5}\\[1em] &=\frac{950.47}{5} = 190.1\ \mathrm{ms} \end{split}

This result we round to 190 ms190\ \mathrm{ms}. Both these results are good, but Olga has got exceptionally good reflexes!

How to use our reaction time calculator

Our reaction time calculator allows you to calculate the reaction time in five repetitions of the experiment. It will calculate the average for you. The correct number of variables will show up when you need it!

Worry not if you want to repeat the experiment a larger number of times. Simply insert each new distance you measure in the relative field on the top of the tool: the new result will overwrite the old one, so keep a notebook at hand or open our average calculator!

🙋 What should you expect from your results? A good reaction time for visual stimuli in humans is between 200 ms and 300 ms.

Calculate the reaction time in other ways: variation on the experiment

Adding other stimuli your brain needs to consider can make this experiment more complicated.

You can, for example, use a word cue to signal that the drop has to be caught. Choose a cue word, for example, "dingus". Now, at every drop, have your friend also say a word (at the exact time of the drop). Every now and then, the word will be "dingus": these are the times you should try stopping the ruler. If you stop the ruler not on cue, don't count the attempt in the average. In this case, your brain needs to integrate a visual and an auditive stimulus.

If you want, you can also add a decision in the process: allow any cue word, but as the ruler drops, have the subject answer the word with an associated word to measure a valid drop; for example, if your friend says "Moon", consider valid the attempt where you answered "night" and not valid the one where you answered "carrot".

🙋 Do you want to bring it to the next level? Try how your implicit association bias affects your reaction time: take inspiration from these tests from Project Implicit and design your own experiment!


What is the average reaction time of a human?

A human's average reaction time depends on the stimulus we are considering. Tactile stimuli are the fastest answered ones, with average reaction times below 0.2 seconds. Visual stimuli fall in the 200-300 ms range. The reaction time to pain stimuli is rather slow, clocking on average at 700 ms.

What is my reaction time if I stop a ruler at 26 cm?

The drop ruler experiment tells you that if you stop the ruler at 26 cm, your reaction time is 230 ms. To find this result, consider the equation for the free fall time and follow these steps:

  1. Convert the distance to meters, and multiply the distance by 2:

    0.26 m × 2 = 0.52 m

  2. Divide the result by the acceleration due to gravity:

    0.52 m / 9.81 m/s² = 0.053 s²

  3. Take the square root of the result:

    √0.053 s² = 0.230 s = 230 ms

How do I calculate the reaction time with a ruler?

To calculate the reaction time with a ruler, follow these easy steps:

  1. Ask a friend to hold a ruler so that it dangles with the zero mark at the bottom, and keep your index and thumb separated by about 8 cm around the zero mark.

  2. Let your friend drop the ruler, and close your fingers as fast as possible on the ruler.

  3. Read the distance d at which you stopped the ruler.

  4. Find the reaction time with the following formula: t = √(2 × d/g) where g is the acceleration due to gravity.

What is a good reaction time in the ruler drop experiment?

A good reaction time you can compute with the ruler drop experiment is around 220 ms. This is also the average reaction time for a visual stimulus followed by a motorial response. Try to reduce it! Be more attentive and rested, or remove any distractions from the room.

Davide Borchia
Read how to perform this experiment by referring to the section "How to calculate the reaction time" in the text.
First attempt
Reaction time
Second attempt
Reaction time
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