‘Square feet’ is the workhorse unit of home improvement, real estate and landscaping. At its core it’s a single multiplication, but the details — converting units and handling odd shapes — are where mistakes creep in. This guide is the plain-English reference for all of it.
What’s in this guide
The square feet formula
Unit conversions to square feet
| From | Operation | To square feet |
|---|---|---|
| Square inches | ÷ 144 | 1,440 sq in = 10 sq ft |
| Square yards | × 9 | 5 sq yd = 45 sq ft |
| Square meters | × 10.7639 | 10 sq m = 107.6 sq ft |
| Acres | × 43,560 | 0.5 acre = 21,780 sq ft |
| Square centimeters | ÷ 929.03 | 10,000 sq cm = 10.76 sq ft |
Square feet of other shapes
| Shape | Area formula |
|---|---|
| Rectangle / square | length × width (or side²) |
| Triangle | ½ × base × height |
| Circle | π × radius² |
| Trapezoid | ½(a + b) × height |
| Parallelogram | base × height |
Worked example
A room 20 ft long and 14 ft wide, with an 18-inch bump-out (1.5 ft) 4 ft wide:
| Piece | Calculation | Area |
|---|---|---|
| Main room | 20 × 14 | 280 sq ft |
| Bump-out | 4 × 1.5 | 6 sq ft |
| Total | — | 286 sq ft |
Divide inches by 12 to get feet (18 in ÷ 12 = 1.5 ft) before you multiply. This one step prevents most errors.
Odd-shaped rooms
There is no special formula for an L-shape or a bay — just split it into rectangles (and the occasional triangle), calculate each, and sum. The composite shape calculators on this site automate exactly this.
Common mistakes
Length + width gives a perimeter-like number, not area. Square feet come from multiplication.
Convert everything to feet first. 10 ft 6 in is 10.5 ft, not 10.6.
Keep decimals through the calculation and round only the final answer.
Key takeaways
- Square feet = length × width, both in feet.
- Convert inches to feet (÷ 12) before multiplying.
- Other shapes use their own area formula.
- Split odd rooms into rectangles and add.
Related calculators & guides
Frequently asked questions
- How do I calculate square feet?
- Multiply length by width when both are in feet. A space 20 ft long and 14 ft wide is 20 × 14 = 280 square feet. For other shapes, use that shape's area formula.
- How do I convert to square feet from other units?
- From square inches divide by 144, from square yards multiply by 9, from square meters multiply by 10.764, and from acres multiply by 43,560. Always convert linear measurements to feet before multiplying.
- How do I find square feet of an odd-shaped room?
- Divide it into rectangles and triangles, calculate each area, and add them. This works for L-shapes, T-shapes and any composite outline.
- What is the difference between feet and square feet?
- Feet measure length (one dimension). Square feet measure area (length × width, two dimensions). You multiply two feet measurements to get square feet.