Weirdly Accurate · Magic Theatre

Optical Illusion Test: How Easily Are You Fooled?

Five classic size illusions on a magic-theatre stage. Resize B until it looks like A, then the rulers show exactly how far your eyes were fooled.

Raise the curtain

Privacy · Terms

How easily do optical illusions fool you?

This optical illusion test measures how far five classic size illusions move your own eyes, with one number for each illusion instead of a yes or no. It uses the method of a 2017 laboratory study in which 59 adults adjusted classic size illusions until the two parts looked equal, and after each round it shows that study’s average next to your own result. Being fooled is not a sign of poor eyesight, and the test is not an eye exam.

This test puts five classic size illusions on a small magic-theatre stage. In each round you resize B until it looks the same as A; then two rulers lift off the figure and lie side by side, and you see exactly how far your eyes were moved, as a percentage. It takes about a minute, works on a phone, and ends with a shareable result card.

What the test measures

Five rounds, one illusion each, all measured the same way: you set B until it matches A, and the gap between your setting and true equality is your result for that illusion.

The five illusions

  • The Müller-Lyer illusion: two rods, one with arrowheads and one with tails
  • The Ebbinghaus (Titchener) illusion: an apple among small cherries and an apple among large oranges
  • The Delboeuf illusion: the same pie on a snug small plate and on a wide large plate
  • The Ponzo illusion: two planks laid across railway tracks that converge into the distance
  • The vertical–horizontal illusion, as a top hat whose height you match to the width of its brim

How each round is scored

  • Your setting is read as how much bigger or longer the illusion made one part look, shown as a percentage
  • Within 5% of true equality counts as not fooled — roughly how precisely people can match two lengths at all
  • Pushing past equality the other way is shown as overcorrecting, not counted as being fooled
  • Where a published average exists, it appears next to your result for comparison

What you get

  • A result for each illusion, and the one that fooled you most
  • A share card and a challenge link a friend can play against
  • No account: your answers stay on your device

Optical illusion FAQ

Is this test free? Do I need to sign up to see my result?

Yes, it’s free, and there’s nothing to sign up for: no account, no email, no payment. Your result appears on this page the moment you finish, and you can share it or play again straight away.

Why do optical illusions fool the brain?

Each of the five figures plays on a different habit of how the visual system judges size, and researchers still argue over the details. This page doesn’t spell them out before you play, because knowing which way a figure pushes changes how you set it. Instead, each round shows which part fooled you, which way and by how much as soon as you confirm, with the published average beside it.

Is it bad if I fall for optical illusions?

No. Falling for these figures is what they were designed to do, and seeing the illusion is no sign that anything is wrong. How strongly you are fooled says nothing about intelligence or eyesight, and illusion strength varies a lot from person to person and with small changes in how a figure is drawn.

How is the percentage calculated?

Each round asks you to make B match A, and your result is how much bigger or longer the illusion made one part look, in percent; the round names that part as soon as you confirm. A result within 5% of equal counts as not fooled, and a negative result means you overcorrected, pushing past equal the other way.

If one illusion fools me, will the others fool me too?

Not necessarily. Researchers disagree on how closely different illusions go together: several studies found that susceptibility to one size illusion predicts little about another, while a large 2023 study found a factor the illusions share alongside differences between them. That is why this test reports each illusion on its own instead of adding them into one score.

Do children see optical illusions the same way as adults?

Not always. In a study of the Ebbinghaus illusion, children younger than about seven were hardly affected, and ten-year-olds were still less affected than adults.

How long does the optical illusion test take?

About a minute: five rounds, each a single adjustment. It works on phones and computers, in 14 languages.

Where the numbers come from

The averages shown in the test come from a 2017 laboratory study that used the same method of adjustment with its own drawings, so treat them as a rough reference rather than a norm for this exact test.