Square footage is the number you need before buying flooring, paint, turf, or tiles — get it wrong and you're either short mid-project or paying for material you'll never use. The maths is simple for a plain rectangle, and only a little more involved for odd-shaped rooms.
This guide covers how to calculate square footage for any space, including L-shapes and circles, and how much extra to buy for waste.
What you need
- ✓A tape measure or laser measure.
- ✓A pen and paper (or a calculator) to add up sections.
- ✓The material's coverage and a note of any 'waste' allowance it suggests.
Step-by-step
- 1
Measure a simple rectangle
For a rectangular room, measure the length and the width in feet, then multiply them: length × width = square footage. A room 12 ft by 10 ft is 120 square feet. Measure to the widest points and round up slightly.
- 2
Break odd shapes into rectangles
For an L-shaped or irregular room, split it into rectangles, calculate each one's area, then add them together. Sketching the space and labelling each section keeps you from double-counting or missing an area.
- 3
Handle circles and triangles
For a circular area, square the radius (half the diameter) and multiply by 3.14 (π). For a triangle, it's half the base times the height. Add these to any rectangular sections for the total.
- 4
Subtract areas you're not covering
For flooring or turf, subtract fixed features you won't cover — kitchen islands, a fireplace hearth. For paint, calculate wall area (perimeter × height) and subtract doors and large windows.
- 5
Add a waste allowance
Always buy more than the bare square footage. Flooring and tile makers typically suggest adding 5–10% for cuts, mistakes and future repairs; more for diagonal layouts or complex rooms. Round up to whole boxes.
Examples
- An L-shaped living room split into a 12×10 (120 sq ft) and a 6×8 (48 sq ft) section totals 168 square feet.
- For 168 sq ft of flooring, adding a 10% waste allowance means buying for about 185 sq ft — rounded up to the next full box.
Tips
- →Rectangle area is simply length × width in feet.
- →Split odd rooms into rectangles and add the areas together.
- →Add 5–10% (or more) for waste on flooring and tile.
- →For paint, use wall area (perimeter × height) minus doors and big windows.
- →Measure twice; a small error scales across a whole room of material.
Common mistakes
- Buying the exact square footage. Add a 5–10% waste allowance so cuts and mistakes don't leave you short.
- Forgetting to subtract fixtures. Deduct islands, hearths, doors and large windows from the area you're covering.
- Mismeasuring odd shapes. Split them into rectangles, sketch each, and add — don't guess a single figure.
- Mixing units. Measure everything in the same unit (feet) before multiplying, or convert first.
Conclusion
Square footage is length × width for a rectangle, and the sum of rectangles for anything odd — plus a 5–10% waste allowance so you don't run short. Measure carefully, subtract what you won't cover, round up to whole boxes, and your flooring or paint project starts with the right number.