How to Calculate Square Footage
Square footage is area measured in square feet. Multiply length by width for rectangular spaces. For irregular rooms, break the area into simple shapes, calculate each, and add them together.
Area Formulas
| Shape | Formula |
|---|---|
| Rectangle | A = l × w |
| Rectangle Border | A = (l+2b)(w+2b) − l×w |
| Circle | A = πr² |
| Circle Border | A = π(r+b)² − πr² |
| Ring | A = π(D/2)² − π((D−2b)/2)² |
| Triangle (edges) | A = √(s(s−a)(s−b)(s−c)) — Heron's formula |
| Triangle (base/height) | A = ½ × b × h |
| Trapezoid | A = ½(b₁+b₂) × h |
| Sector | A = (θ/360) × πr² |
| Parallelogram | A = b × h |
Measuring Tips
- Measure to the nearest inch, then convert: divide inches by 12 to get feet
- For L-shaped rooms, split into two rectangles and add the areas
- Include closets and alcoves in your total
- Measure from wall to wall, not baseboard to baseboard
- Take 2-3 measurements per wall and average them — walls are rarely perfectly straight
Example: L-Shaped Room
A room that's 15×12 with a 5×8 alcove:
- Main area: 15 × 12 = 180 sq ft
- Alcove: 5 × 8 = 40 sq ft
- Total: 220 sq ft
Common Uses for Square Footage
- Flooring: Calculate area and add 10% for waste. Use our Flooring Calculator for boxes and cost
- Paint: One gallon covers 350-400 sq ft. Calculate wall area (perimeter × ceiling height), subtract doors/windows. See our Paint Calculator
- HVAC sizing: Roughly 20 BTUs per sq ft for cooling. A 1,500 sq ft home needs about 30,000 BTUs (2.5 tons)
- Real estate: Price per sq ft is the standard comparison metric. Average US home price is roughly $150-250/sq ft depending on market
- Rent pricing: Commercial leases are quoted per sq ft per year. $25/sq ft means a 1,000 sq ft office costs $25,000/year
Unit Conversions
- 1 square foot = 0.0929 square meters
- 1 square meter = 10.764 square feet
- 1 square yard = 9 square feet
- 1 acre = 43,560 square feet (roughly 209 × 209 ft)
- 1 hectare = 107,639 square feet = 2.471 acres