Area Calculator guide
How to Work Out Square Footage for Flooring and Paint
To find square footage, measure the length and width in feet and multiply them. A room 14 feet by 12 feet is 168 square feet. For flooring, add 10% for waste — or 15% if the planks run diagonally or the room is an awkward shape.
The basic calculation
Measure the length and the width of the room in feet, then multiply them together.
A room 14 feet long and 12 feet wide is 14 × 12 = 168 square feet.
If your measurements include inches, convert them to a decimal first rather than trying to work in feet and inches. 14 feet 6 inches is 14.5 feet, because 6 inches is half a foot. Nine inches would be 0.75 feet.
Always add waste
This is the part that catches people out, and running short partway through a floor is a genuinely miserable experience — the replacement batch may not match.
- Standard rooms, straight lay — add 10%
- Diagonal or herringbone patterns — add 15%, sometimes 20%
- Large-format or patterned tile — add 15%, since matching the pattern wastes more
- Rooms with many alcoves, doorways or angles — add 15%
Applying the waste allowance
For our 168 square foot room with a standard 10% allowance: 168 × 1.10 = 185 square feet to buy.
Buy in whole boxes, rounding up. If a box covers 20 square feet, 185 needs ten boxes rather than nine and a bit.
Keep any full leftover box rather than returning it. Floors get damaged, and having matching material from the same production batch is worth considerably more than the refund.
L-shaped and awkward rooms
Do not try to find a single clever formula. Split the room into rectangles, work out each one, and add them up.
For an L-shape, draw a line across it to make two rectangles. Measure each, calculate each, add the results. An L that splits into 10 × 12 and 6 × 8 gives 120 + 48 = 168 square feet.
For a room with a bay window or alcove, treat each protrusion as its own small rectangle and add it on. Where a shape is genuinely irregular, splitting it into rectangles and one or two triangles will get you within a couple of percent, which the waste allowance covers.
Paint is a different calculation
For paint you want the area of the walls, not the floor, and that changes what you measure.
Work out the perimeter of the room, then multiply by the ceiling height. For our 14 × 12 room with 8 foot ceilings: perimeter is 2 × (14 + 12) = 52 feet, and 52 × 8 = 416 square feet of wall.
Subtract roughly 20 square feet per door and 15 per average window. With one door and two windows, that is 416 − 20 − 30 = 366 square feet.
Then check the coverage figure on the tin — typically 350 to 400 square feet per gallon — and remember to double it if you are applying two coats, which you almost always should.
Measuring properly
A few habits that prevent expensive mistakes:
- Measure at floor level for flooring. Walls are rarely perfectly straight, and the measurement at waist height can differ by an inch or two.
- Measure each wall at both ends. Old rooms are frequently not rectangular, and if the two ends differ, use the larger.
- Include the space under where furniture will sit, and the doorway thresholds.
- Write measurements down as you take them rather than trusting your memory across four walls.
- Measure twice. It costs a minute and it has saved a great many floors.
