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Educator’s Toolkit: Find the Centre of (almost) Any Shape
Educator’s Toolkit: Find the Centre of (almost) Any Shape
Summary ✨
Whether you're building a cardboard rocket ship, designing a spinning top, or just trying to hang something perfectly on the wall, finding the centre of a shape is one of those surprisingly handy skills that makers use all the time. The good news? It's way easier than it sounds, and you don't need to be a geometry whiz to nail it.
Here are some tried-and-true methods that work for squares, circles, triangles, and don’t require any special tools or mathematics!
Method #1: Ruler & Diagonal Lines
(Best for Squares & Rectangles)
Got a ruler? This classic geometry trick takes about 30 seconds.
What you need: A ruler, a pencil, and your cardboard shape.
The steps:
-
- Draw a straight line from one corner of your shape to the opposite corner (this is a diagonal).
- Draw another line from the remaining two corners.
- The point where the two diagonal lines cross is the centre!
This method works great for rectangular cardboard pieces, and it’s a good one to teach students because the logic is visible - the two diagonals will always meet in the middle of the shape.
Maker Tip: No ruler? A strip of cardboard or a sheet of paper works just as well! Don’t be afraid to improvise.
Method #2: Fold a Paper Template
(Best for Circles)
This is a quick and fairly accurate way to find the centre of a circle.
What you need: A piece of paper wider than your shape.
The steps:
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- Place your shape on a blank piece of paper and trace around it with a pencil.
- Cut the paper circle out.
- Fold your circle in half one way, lining up the edges as best as you can. Gently crease the fold and unfold it.
- Now fold your circle in half the other way. Crease and unfold.
- See where the two lines cross? That’s the centre!
- Mark the centre on your shape or use the Pointy Bit of a tool.
This works well for rectangles, squares, and circles. It can also be applied to irregular shapes, just get as close as you can to the middle with each fold, and you’ll still land very near the centre.
Method #3: Use a Framing Square or Paper
(For Circles)
While you can use a framing square to find the centre of a circle, the same trick can be done with the corner of a simple piece of paper!
The steps:
-
- Place the paper on your circle so that the corner just touches the edge.
- Mark where the paper meets the edge of the circle in both directions.
- Draw a line connecting the two marked points.
- Rotate your circle and repeat steps 1-3, with the paper in a different position (don't forget to check that the corner is touching the edge of your circle!).
- The point where your two lines cross is the centre of your circle!
This method makes use of the precise right angle that is a feature of an everyday piece of paper. You can also use other objects that have a 90-degree corner, as long as they fit neatly across your circle shape.
Why find the centre?
When making things, the centre is an anchor point. It helps you:
-
- Punch holes in exactly the right spot
- Balance spinning pieces like wheels, propellors and gears
- Align decorations symmetrically
- Join pieces together cleanly and evenly
How to apply to (almost) any shape
We've outlined some techniques here that will help you find the centre of standard geometric shapes such as rectangles, circles and triangles. But what if your shape is irregular or even organic?
The good news is that these same techniques can be applied to more complex forms. Try approximating a rectangle or circle that covers the length and width of your shape, and then apply one of the techniques in this guide.
The Maker Academy
Want more cardboard maker tips and tricks like this? Head over to the Makedo Resource Hub - it’s packed with tips, tricks, and step-by-step guides to help makers build bigger and better.
