Updated July 8, 2026
To measure a room's square footage, use a tape measure to record the length and width in feet, then multiply them together. A 12-foot by 15-foot room is 180 square feet (12 times 15 equals 180). For rooms that are not a simple rectangle, divide the space into separate rectangles, calculate each one, and add the totals.
What you need
- A 25-foot tape measure (a laser measuring tool works well for large rooms)
- Pencil and paper or a phone to note dimensions
- A sketch of the room layout, even a rough one, helps avoid mistakes
The basic rectangle method
- Measure the longest wall from corner to corner. Write it down.
- Measure the adjacent wall, perpendicular to the first. Write it down.
- Multiply length times width to get square feet.
- Example: 13 ft times 11 ft equals 143 sq ft.
Splitting an irregular room into rectangles
Split an L-shaped room into two rectangles. Measure each rectangle separately and add the two results. An L-shaped living room might be a 12x18 section (216 sq ft) plus an 8x10 section (80 sq ft), for a total of 296 square feet. Use our square footage calculator to handle L-shaped and multi-section rooms automatically once you have your two sets of dimensions.
Reference chart by room size
| Room dimensions | Square footage |
|---|---|
| 10 x 10 | 100 sq ft |
| 10 x 12 | 120 sq ft |
| 12 x 12 | 144 sq ft |
| 12 x 15 | 180 sq ft |
| 14 x 14 | 196 sq ft |
| 15 x 20 | 300 sq ft |
Flooring math vs. paint math
These two projects need different numbers from the same room. For flooring, measure the floor area only, length times width of the floor. For painting, you need wall area: the room perimeter, all four walls added together, multiplied by ceiling height, then doors and windows subtracted. Grab both figures on the same visit with a tape measure so you are not remeasuring the room twice for two different projects. See how much flooring to order and how much paint to buy for what to do with each number.
Measuring in inches and converting
If your tape shows inches, divide each measurement by 12 to convert to feet. A room that measures 147 inches by 168 inches is 12.25 feet by 14 feet, or about 171.5 square feet. It is easier to measure directly in feet by reading the large numbers on the tape and estimating the fraction of a foot for whatever inches are left over.
Skip the manual math
Enter your dimensions, including L-shapes, and get area instantly.