Square Footage Calculator
Area in square feet, square meters, and acres from length and width.
What it does
Square footage is the area of a rectangle: length times width. Nearly every home project starts here, from flooring boxes to paint gallons to mulch yards, and the same number feeds all of them once measured right.
The tool above takes length and width in feet, inches, yards, meters, or centimeters. It returns square feet, square meters, and acres at once, so listings, materials, and land records all read off one pass.
Odd shapes split into rectangles. L shapes become two boxes, rooms with alcoves become a main box plus the nook. Measure each part at its longest points, add the areas, and subtract fixed obstacles like fireplaces only when they truly eat floor space.
Round the plan, not the tape. Keep decimals through the math and round once at ordering, since early rounding on big areas drifts by whole boxes.
How to use
- Measure length and width in matching units.
- Pick that unit so conversion happens inside the tool.
- For L shapes, measure two rectangles and add them with two passes.
- Read square feet for US materials, square meters for metric ones.
Formula
- length, width
- Longest straight measures of the rectangle, same unit both.
- 10.7639
- Square feet in one square meter (3.28084 squared).
- 43,560
- Square feet in one acre, fixed by US survey definition.
Units square with the sides: feet times feet give square feet, and converting sides first keeps one path for every input unit. Circles use 3.14 times radius squared instead.
Worked example
Example: 20 by 15 ft room
Length 20 ft, width 15 ft.
- Multiply: 20 x 15 = 300.00 ft2.
- Metric: 300 / 10.7639 = 27.87 m2.
- Acres: 300 / 43,560 = 0.0069 acres.
- Flooring at 10% waste: 300 x 1.10 = 330 ft2 to buy.
Reference table
| Space | Size | Area |
|---|---|---|
| Parking space | 9 x 18 ft | 162 ft2 |
| Bedroom | 12 x 12 ft | 144 ft2 |
| Two car garage | 20 x 20 ft | 400 ft2 |
| Basketball court | 94 x 50 ft | 4,700 ft2 |
| Acre lot | about 208 x 208 ft | 43,560 ft2 |
Limits
- Rectangles only. Curves and angles need splitting or a planimeter.
- Measures the footprint, not usable space after thick walls and fixtures.
- Does not add waste. Materials need 5 to 15% on top.
- Survey acres follow legal records, which can differ from tape measures.
Common mistakes
- Mixing units, like feet with inches, without converting first.
- Measuring once. Long tapes sag, so measure twice and average.
- Including closets and halls in room flooring, then overbuying.
- Rounding each wall before multiplying on big areas.
- Reading linear feet off a quote as square feet.
Try it yourself
Quick checks. Answers sit tucked under each question.
A wall is 12 ft long and 8 ft high. Paintable area?
12 x 8 = 96 ft2, before subtracting doors and windows.
How many acres is a 100 x 100 ft lot?
10,000 / 43,560 = 0.23 acres.
Questions
How do I measure an L shaped room?
Split it into two rectangles, measure each, and add. Two passes through this tool give both areas.
What is a square foot?
A 12 by 12 inch square. Nine of them make a square yard.
How many square feet in an acre?
43,560. A square acre is about 208.7 ft per side.
Square feet or square meters for flooring?
US stores quote square feet, European ones square meters. The tool prints both, so either shelf works.
Do I subtract closets?
Only when they keep different flooring. Otherwise include them and cut around.
How much extra flooring should I buy?
Ten percent for straight rooms, fifteen with angles or patterns, more for rare tile.