What is Perimeter?
Six tiny lessons. Play with each one — you'll know perimeter in ten minutes.
1 · Walk around the edge
Press the button and watch the robot walk all the way around the rectangle. Every step it takes gets counted — the total distance it walks is the perimeter.
2 · Squares & rectangles
Drag the sliders. The shape changes size — and the perimeter changes with it. See how the formula is just a quick way of adding all four sides.
3 · Triangles & polygons — add every side
Click each side to tick it off into the running total. Perimeter doesn't care how many sides a shape has — add them all!
4 · Irregular shapes
Odd shapes are no harder. Click the sides in ANY order — start anywhere you like. The total is still just every side added up.
5 · Working backwards — the missing side
Sometimes you know the perimeter but one side is hiding. Reveal the strategy step by step: take the perimeter, subtract the sides you know, and what's left is the missing side.
6 · Perimeter in real life
People use perimeter all the time — here are four favourites.
🚧 Fence a garden
A garden 5 m by 3 m needs a fence all around: P = 2 × (5 + 3) = 16 m of fencing.
🖼️ Frame a photo
A photo 20 cm by 10 cm needs P = 2 × (20 + 10) = 60 cm of frame.
🎂 Ribbon around a cake
A square cake tin 25 cm wide needs P = 4 × 25 = 100 cm of ribbon.
⚽ Walk the soccer field
A field 90 m by 45 m: walking all the way around is P = 2 × (90 + 45) = 270 m.