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One Quick Try

Guess the Angle

An angle is drawn at a random tilt. How many degrees is it? Estimate by eye.

Type
Perception
Takes
about 1-2 min
Result in
degrees off

Guess the Angle

~1-2 min

  1. An angle is drawn, tilted a different way each time.
  2. Type how many degrees you think it is, from 0 to 180, and press Enter.
  3. 10 angles. Your score is how far off you are on average.

No protractor, no clock. Just your eye.

Your result: — ° off

How it's measured

Try another challenge

How does the guess the angle game work?

An angle appears: two lines meeting at a point, with a small arc marking the angle between them. You type how many degrees you think it is and press Enter. After each guess the true size is shown, along with a dashed line where your guess would have put the second arm. There are 10 angles, each between 5° and 175°, and no clock.

How is your result calculated?

Each guess is compared with the true angle, in whole degrees. Your result is your average miss: how far off you were on average, whether too high or too low. You also see your closest guess, how many you got exactly right, and your tendency, the average of your misses with their direction, which shows whether you lean towards guessing high or low.

The whole angle is turned to a random direction each time, so neither line lines up with the edges of your screen. Otherwise the screen's edges would act as a ruler for one of the arms.

How to estimate angles better

  • Start from a right angle. First decide whether the angle is smaller or bigger than a square corner, 90°. That alone rules out half the answers.
  • Use halves and thirds. Half a right angle is 45°, a third is 30° and two thirds is 60°. Most angles are easier to place between two of these than from scratch.
  • For wide angles, look at what is missing. An angle near 180° is a nearly straight line: judge how far it is from straight, and subtract.
  • Ignore the tilt. The same angle can look different when it is turned. Try to see the gap between the arms, not their directions.

What can change your result

  • Your screen's shape. A display set to stretch the picture, or a zoomed browser on some devices, can distort angles slightly. At normal settings, angles are drawn true.
  • Practice. Seeing the true size after each guess is feedback, so your later guesses in a run can benefit from the earlier ones.

This is an estimation game, not an assessment of anything. For another test of judging shapes by eye, try the Mental Rotation Test, or draw one yourself in Draw a Perfect Circle.

Questions

Can the angle be more than 180 degrees?
No. Every angle here is between 5° and 175°, and the arc shows which side of the lines is meant.
Why is the angle tilted?
So the screen's edges can't be used as a guide. A line lying exactly flat would give you one arm for free.
What does the tendency mean?
The average of your misses with their direction. A positive tendency means you usually guessed too high, a negative one too low.
Do I need to type a whole number?
Yes: a whole number of degrees from 0 to 180. The true angles are whole numbers too.
How can you estimate an angle without a protractor?
Compare it with angles you know. A square corner is 90°, half of it is 45°, and a third and two thirds of it are 30° and 60°. Decide which two of these your angle falls between, then judge where in that gap it sits. For wide angles, judge how far it is from a straight line, 180°, and subtract.