November 7, 2024, 1:15 pm | Read time: 2 minutes
A folding ruler belongs in every toolbox and is therefore part of the basic equipment for DIY enthusiasts. However, many people don’t know this: A folding ruler can be used not only to measure lengths but also angles. The 3-4-5 trick helps.
Whether you want to hang a picture on the wall or build a shelf – a folding ruler is indispensable for many projects at home. The folding ruler makes it easy to measure lengths, depths, and heights. However, the folding ruler can be used not only to measure distances but also angles. And this is where the 3-4-5 trick with the folding ruler comes into play. myHOMEBOOK editorial manager Felix Mildner explains what’s behind it.
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How the 3-4-5 ruler trick works
This method, whose name is based on a simple sequence of numbers, makes it easy to check right angles. 90-degree angles are relatively common – but they do not always have the desired precision. If you know the 3-4-5 trick, you can also check right angles with a folding rule.
The numbers represent the aspect ratio of a triangle. This is how the method works, for example, with a wooden board on which you want to check the angle:
- First, measure three (or 30) centimeters on one side of the board, starting from the corner with the right angle you want to check. Mark this point with a pencil.
- Then, place it on the other side or other leg of the angle and measure four (or 40) centimeters. Mark the position here, too.
- Then, measure the diagonal, i.e., the distance between the two markings. If this is exactly five centimeters (or 50) long, the edge is a perfect right angle at 90 degrees.
There is a bit of math behind this – specifically, the Pythagorean theorem, which you may remember from school. It reads: a2 + b2 = c2. The letters “a” and “b” stand for the two legs, while “c” stands for the diagonal. In our case, the calculation is 3×3 + 4×4 = 5×5. But don’t worry; you can use this trick without any previous mathematical knowledge.
Of course, other lengths are also possible when measuring with the 3-4-5 trick, but the ratio should be correct. For example, the measurements could also be 60, 80, and 100 centimeters. Instead of using a folding ruler, you can also use a tape measure.