How to Calculate Square Footage
Square footage is length times width - the only trick is splitting an odd-shaped room into pieces you can measure. Here is the method for a room, a wall and a whole house, plus a table of common room sizes.
By the Calculate My Reno Team / Published
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Open the Square Footage Calculator
Square footage is just length times width. The only thing that makes it tricky is a room that is not a clean rectangle - and the fix is always the same: break it into simple shapes, measure each, and add them up.
Skip the math
Enter each part of the room as a rectangle, triangle or circle and the square footage calculator adds them up and shows the total in square feet, square metres, square yards and acres. You can type feet and inches straight off the tape. The rest of this guide is the method behind it.
The basic formula
area = length × width
Measure the length and the width in feet, multiply, and the answer is in square feet. A room 12 ft by 10 ft is 12 × 10 = 120 sq ft.
Working in inches? Divide each measurement by 12 to turn it into feet first. A wall 150 in by 96 in is 12.5 ft by 8 ft, so 12.5 × 8 = 100 sq ft.
Square footage of a room
- Measure the length of the room wall to wall.
- Measure the width the same way.
- Multiply the two.
For a plain rectangle that is the whole job. Round measurements to the nearest inch or two - precision past that will not change how much material you need to buy.
L-shaped and irregular rooms
A room that is not a rectangle is just two or more rectangles (and sometimes a triangle):
- Draw the room and divide it into rectangles with a couple of pencil lines.
- Measure and calculate each rectangle.
- Add the pieces together.
For an angled wall, the leftover triangle is base × height ÷ 2 - a triangle 6 ft along the base and 4 ft tall is 6 × 4 ÷ 2 = 12 sq ft. For a curved bay, treat it as part of a circle (π × radius², where π is about 3.14 and the radius is half the width across) - a half-round bay 4 ft across has a 2 ft radius, so π × 2² ÷ 2 ≈ 6.3 sq ft. Add each piece as its own shape in the calculator and it totals them for you.
Common room sizes
Floor area for a rectangular room, in square feet and square metres:
| Room size | Square feet | Square metres |
|---|---|---|
| 8 × 10 ft | 80 sq ft | 7.4 m² |
| 10 × 12 ft | 120 sq ft | 11.1 m² |
| 12 × 12 ft | 144 sq ft | 13.4 m² |
| 12 × 15 ft | 180 sq ft | 16.7 m² |
| 15 × 20 ft | 300 sq ft | 27.9 m² |
| 20 × 20 ft | 400 sq ft | 37.2 m² |
Floor area or wall area?
Be clear about which surface you are measuring:
- Floor square footage is length × width - what you cover with flooring, tile or carpet.
- Wall square footage is wall length × wall height - what you cover with paint, wallpaper or wall tile. A room has one floor but four walls, so add the walls together and subtract the doors and windows.
Worked example
An L-shaped living room: a main part 16 × 12 ft, plus a 6 × 8 ft alcove off one end.
- Main part: 16 × 12 = 192 sq ft.
- Alcove: 6 × 8 = 48 sq ft.
- Total: 192 + 48 = 240 sq ft (about 22.3 m²).
Whole house rather than one room? See how to calculate the square footage of a house, and to picture the result, how big is 1,000 square feet.
Frequently asked questions
What is the formula for square footage?
Area equals length times width, with both measured in feet. A room 12 ft long and 10 ft wide is 12 × 10 = 120 square feet. If you measured in inches, divide each measurement by 12 to get feet first, or multiply the two inch figures and divide by 144.
How do I calculate square footage of an irregular room?
Split the room into rectangles and triangles, work out each one, and add them together. An L-shaped room is two rectangles; a room with an angled wall is a rectangle plus a triangle. Measure each piece, calculate its area, and total them - which is exactly what the square footage calculator does when you add each shape.
How do I calculate square footage from inches?
Convert each measurement to feet by dividing by 12, then multiply. A wall 150 inches by 96 inches is 12.5 ft by 8 ft, which is 100 square feet. Or multiply the inches directly (150 × 96 = 14,400 square inches) and divide by 144 to get 100 square feet.
Is square footage the same as the floor size?
For a floor, yes - floor square footage is the area you would cover with flooring or carpet. Wall square footage is different: it is the wall length times its height, used for paint, tile or wallpaper. Always be clear which surface you are measuring, because a room has one floor area but four walls.
How accurate do I need to be?
For buying materials, measure to the nearest inch or two centimetres - small errors barely move the total, and material calculators add a waste margin anyway. For an official figure like an appraisal or a listing, follow the local measuring standard, because what counts as living area is defined precisely.