Form a Perfect Right Angle Using Just String

A perfect right angle whenever you need one; marking out a football field or a building plot, checking a fence, this method always gives 100% accurate right angles.


  1. Take a length of string (it can be a metric length, or an imperial length, or just any old length, it won't affect the accuracy of our method).
  2. Tie a small loop in the end of your string.
  3. Wrap your string round some convenient object, such as the back of a chair, counting off 5 turns.
  4. Tie another small loop in your string.
  5. Wrap your string a further 4 times round your chair back, and again tie a small loop.
  6. Wrap your string a further 3 times and tie a final small loop. Cut off the remaining string and give it away.
  7. Unravel your string from the chair and get your willing helpers to each hold a loop. Put the two end loops together.
  8. Each person needs to pull against the other 2 people (you will have worked out you need 3 people for this altogether), and as they do so, the string forms a perfect right angled triangle.


  • Try to keep your wrappings as accurate as you can, don't choose a soft chair, or a sloping back chair, and don't wrap the string over itself.
  • Why? You will remember Pythagoras, that old Greek with the honour of having found that the square of the hypotenuse is equal to the sum of the squares of the other two sides of the triangle. The hypotenuse is the side of the triangle opposite the right angle, and in this case, this was the part of the string wrapped 5 times round the chair.
    • 5x5 = 25
    • 4x4 = 16 3x3 = 9 16 + 9 = 25 QED


  • Don't get yourself tangled up in the string!

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