Transparent method
The formula
Worked example
Example inputs
How to interpret the result
An irregularly shaped room doesn't reduce to one length times one width, so getting an accurate area means measuring the room's longest points as if it were a full rectangle and then separately subtracting any fixed obstructions, rather than trying to average out the irregular edges into a single approximate dimension.
Before you rely on it
What to check
Measure to the longest points of an irregular room and subtract built-in obstructions separately, rather than eyeballing one averaged length and width.
The common error
Where people go wrong with square footage calculator
Treating an irregular room as a perfect rectangle using one estimated average length and width. That approach both overstates and understates different parts of the room at once, and the two errors don't reliably cancel out.
Sensitivity evidence
How length (ft) changes the area (sq ft)
| Length (ft) | Area (sq ft) | Area (sq yd) |
|---|---|---|
| 12 | 144 | 16 |
| 14 | 168 | 18.7 |
| 15worked example | 180 | 20 |
| 17 | 204 | 22.7 |
| 18 | 216 | 24 |
Every input, tested
Which input moves the area (sq ft) most
| Input | Tested from | To | Area (sq ft) at each end | Swing |
|---|---|---|---|---|
| Length (ft) | 14 | 17 | 168 to 204 | 36 (20%) |
| Width (ft) | 11 | 13 | 165 to 195 | 30 (17%) |
Two variables at once
Area (sq ft) by length (ft) and width (ft)
| Length (ft) \ Width (ft) | 10 | 12 | 14 |
|---|---|---|---|
| 12 | 120 | 144 | 168 |
| 14 | 140 | 168 | 196 |
| 15 | 150 | 180 | 210 |
| 17 | 170 | 204 | 238 |
| 18 | 180 | 216 | 252 |
Step by step
The worked example, input by input
| Input | Value used |
|---|---|
| Length (ft) | 15 |
| Width (ft) | 12 |
| Area (sq ft) | 180 |
| Area (sq yd) | 20 |
Where the inputs come from
Enter the length and width of the space in feet. For an irregular room, divide the floor into rectangles, measure each and add them, subtracting areas such as closets you do not want to include. Measure wall to wall at the floor, not including wall thickness for the interior area, and use the same unit for both. The tool returns square feet and square yards.
When the result stops applying
Measuring errors of a few inches matter in small rooms. The rectangle formula does not handle angled walls, bays or curved rooms. Ceiling height does not affect floor area, but it matters for wall and volume calculations.
What to compare it with
Use the tile, flooring, carpet and paver calculators for materials, the paint and wallpaper pages for walls, and the rectangle area calculator for shapes. The price per square foot page relates area to price, and the area converter changes units.
People also ask
Frequently asked questions
How do I calculate square footage?
Multiply the length by the width in feet. A 15 by 12 foot room is 180 square feet.
How do I measure an L-shaped room?
Split it into two rectangles, calculate the area of each and add the results together, subtracting any part you do not want to include.
How many square feet are in a square yard?
Nine, since a yard is three feet on each side, and three feet times three feet is nine square feet.