Square footage is the starting point for flooring, tile, paint, sod and almost every surface estimate. For a plain rectangle it is one multiplication. The skill worth learning is breaking an awkward room into shapes you can measure, then adding them up.
Rectangles and squares
Multiply length by width. A room 12 feet by 10 feet is 120 square feet. Measure to the longest points and round up slightly, since walls are rarely perfectly straight and being a little over never hurt an estimate. Measure twice if the number feeds an expensive order like hardwood flooring.
L-shaped and irregular rooms
Split the space into rectangles, work out each one, and add them. A room shaped like an L is just two rectangles. Draw it on paper, divide it into boxes, measure each box, and total them. This handles almost any layout built from straight walls, including bump outs, alcoves and closets you want to include.
Triangles
For a triangular section, area is one half times the base times the height, where the height is measured square to the base, not along a slanted side. A triangle with a 6 foot base and 4 foot height is 0.5 times 6 times 4, which is 12 square feet. Add it to your rectangle total.
Circles and curves
For a circle, area is pi times the radius squared. A circular patio 10 feet across has a 5 foot radius, so the area is 3.14 times 25, about 78.5 square feet. For a half circle, halve that. For a curved edge that is not a clean half circle, approximate it with a rectangle plus a triangle and accept a small overage.
Worked example: an L-shaped living room
An L-shaped living room splits into a 12 by 16 main rectangle, which is 192 square feet, and a 6 by 8 extension, which is 48 square feet. Together that is 240 square feet. If you are buying flooring, add your waste factor on top of this combined total, not onto each piece separately.
Unit conversions
| From | To | Multiply by |
|---|---|---|
| Square feet | Square yards | 0.111 (divide by 9) |
| Square feet | Square metres | 0.0929 |
| Square metres | Square feet | 10.76 |
Measuring tips
- A laser distance measure beats a tape for wall to wall spans and is more accurate for one person working alone.
- Sketch the room first and write each measurement on the sketch, so you are not holding numbers in your head.
- For flooring and tile, measure the actual floor, not the room listed on a plan, since built outs and fittings change it.