How to measure a room
Take a tape to the floor and measure wall to wall at the widest point. Floors are the surface you are covering, and a wall can lean a little or carry a baseboard, so the height you measure at changes the number more than you would expect.
Odd rooms are rectangles stuck together. Sketch the room, split it into rectangles, and measure each one. An L-shaped living room is one big rectangle and one small one, and a bay window is a third.
Enter inches as a decimal of a foot. Ten feet six inches is 10.5, because six inches is half a foot. It is not 10.6. Do the sum on your phone if you need to: divide the inches by 12.
A worked example
Here is a living room of 16 by 12 feet with an alcove of 8 by 6 feet off one side. These lines come from the same formula the calculator above runs.
16 by 12 ft room with an 8 by 6 ft alcove
- Main room: 16 × 12 = 192 sq ft
- Alcove: 8 × 6 = 48 sq ft
- Total: 192 + 48 = 240 sq ft
- In square yards: 240 ÷ 9 = 26.67 sq yd
Carpet is often sold by the square yard, and most other flooring by the square foot, which is why both are shown. From here the flooring calculator turns the area into boxes with waste, and the paint calculator uses the same measurements for the walls.
Common room sizes
These are typical sizes rather than rules, but they are handy for checking that a number looks right. If your bedroom comes out at 400 square feet, a measurement went wrong somewhere.
| Room | Square feet | Square yards | Square metres |
|---|---|---|---|
| Small bedroom, 10 × 10 | 100 | 11.1 | 9.3 |
| Bedroom, 12 × 12 | 144 | 16.0 | 13.4 |
| Main bedroom, 14 × 12 | 168 | 18.7 | 15.6 |
| Living room, 16 × 12 | 192 | 21.3 | 17.8 |
| Large living room, 20 × 14 | 280 | 31.1 | 26.0 |
| Two-car garage, 24 × 24 | 576 | 64.0 | 53.5 |
Mistakes that cost you material
- Reading inches as decimals. 10 ft 6 in is 10.5, and using 10.6 on both sides of a room adds a couple of square feet of nothing.
- Forgetting the second leg. Measuring only the main part of an L-shape can leave you a whole box short.
- Buying exactly the area. Square footage is the floor and not the order. Flooring and tile need extra for cuts, and the amount depends on the layout.
- Comparing with the listing. A whole-house figure measured from outside the walls will always beat the sum of the rooms measured inside them.
- Counting low attic space. Finished area for a house generally needs a ceiling of about 7 feet, and space under 5 feet does not count at all.
Questions
How many square feet is a 12 by 12 room?
A 12 by 12 room is 144 square feet. Multiply the length by the width, both in feet. That is 16 square yards, or about 13.4 square metres.
How do I find the square footage of an L-shaped room?
Split the L into two rectangles, work out each one, and add them. A 16 by 12 room with an 8 by 6 alcove is 192 plus 48, which is 240 square feet. Open the extra section above and enter the alcove as the added section.
Do closets count in square footage?
Closets inside the walls are usually counted in a home's total, but for buying flooring you measure them as their own small rectangles anyway. Lenders use ANSI Z765 for a whole house, measured from the outside, and that standard does not cover the size of a single room.
How do I change square feet to square yards?
Divide square feet by 9. There are 3 feet in a yard, so a square yard is 3 by 3, which is 9 square feet. A 180 square foot room is 20 square yards.
How do I enter inches?
Enter inches as a decimal of a foot, by dividing them by 12. Ten feet six inches is 10.5, not 10.6. Getting that wrong on both sides of a room is an easy way to be several square feet out.
Why does my number not match the listing or the tax record?
They usually measure differently. A listing built on ANSI Z765 measures from the outside faces of the walls and has rules for low ceilings and basements, while you are measuring inside each room. Tax records may follow neither.
This square footage is a planning estimate from the sizes you typed, not an appraisal or an ANSI measurement of a house. Walls that are out of square and waste from cuts change what you actually buy. Confirm with your supplier and the product label before you order.
Sources and review
- NIST Guide to the SI, Appendix B.9, National Institute of Standards and Technology, 2025.
- Understanding ANSI measurement standards, Wisconsin REALTORS Association, 2022.
Checked in November 2026. Spotted a wrong number? Report it and it goes in the corrections log.
How this is calculated
Every figure below is read from the code that produces the answer, so what is written here is what the calculator ran. The constants were last checked against their sources in November 2026.
The arithmetic
Area of a rectangle
Area = Length × Width
- Length
- Longest side, in feet
- Width
- Shorter side, in feet
Worked through: 16 × 12 = 192 sq ft
Square yards
Square yards = Square feet ÷ 9
- 9
- Square feet in one square yard
Worked through: 108 ÷ 9 = 12 sq yd
The constants, and where they come from
SQ_M_PER_SQ_FT
DefinitionalSquare metres in one square foot
Applies to: Definitional, everywhere
Source: Guide for the Use of the International System of Units (SP 811), Appendix B.9, factors for units listed by kind of quantity, National Institute of Standards and Technology, published 2025-08, read 2026-11.
NIST lists 9.290304 E-02. An exact conversion, so it is stored in full and rounded only for display.
SQ_FT_PER_SQ_YD
DefinitionalSquare feet in one square yard
Applies to: Definitional, everywhere
True by definition, so there is nothing to cite. The derivation is below.
Three feet in a yard, and an area is a length times a length, so 3 × 3 = 9.
What the labels mean
- Definitional:
- true by definition, like the number of inches in a foot, so there is nothing to cite.
If a figure here looks wrong, it may be. Tell us what you found and we will check it against the source and publish a correction if it needs one. How constants are chosen and how often they are reviewed is set out in our methodology.
How to use the square footage calculator
- 1
Pick the shape of the main area
- 2
Measure it in feet and enter the sizes
- 3
Open the extra section to add a second leg or take off a cutout
- 4
Read the total in square feet, yards and metres
- 5
Add it to your project list, or open the calculator for what you are buying
What this calculator assumes
Every estimate here rests on the assumptions below. Where your job differs from one of them, the figure will differ too.
- Each shape is measured in feet, and inches are entered as decimals of a foot
- A circle is measured across its widest point, through the centre
- The added section and the cutout are both rectangles
- This measures the areas you give it. It does not apply the ANSI Z765 rules a lender uses for a whole house
Pro tips
- Sketch the room first and mark each rectangle
- Measure at floor level, because a wall can lean or carry a skirting board
- Measure both opposite walls and use the longer figure for buying material