How to Calculate Square Footage
Rectangle (Most Common)
For rectangular rooms — the most common shape — simply multiply length × width. A 12-foot by 15-foot room is 180 square feet. Always measure in feet (or convert from inches: divide by 12). Measure at the widest points and include closets and alcoves separately.
Shape Formulas
| Shape | Formula | Example |
|---|---|---|
| Rectangle | length × width | 12 × 15 = 180 sq ft |
| Triangle | ½ × base × height | ½ × 10 × 8 = 40 sq ft |
| Circle | π × radius² | π × 5² = 78.5 sq ft |
| Trapezoid | ½ × (a + b) × height | ½ × (8 + 12) × 6 = 60 sq ft |
Flooring Material Estimates
How Much Flooring Do You Need?
When ordering flooring materials, always add a 10% waste factor — the Tile Council of North America recommends 10–15% extra for straight-laid tile and 15–20% for diagonal patterns. Complex room shapes and doorways increase waste.
| Material | Avg. Cost/sq ft | Coverage per Box |
|---|---|---|
| Laminate | $1.50–$5 | 20–25 sq ft |
| Hardwood | $5–$12 | 20 sq ft |
| Tile (ceramic) | $2–$8 | Varies by size |
| Vinyl plank | $2–$7 | 20–24 sq ft |
| Carpet | $2–$8 | Sold per sq yd |
Paint Coverage Calculator
How Much Paint per Room?
One gallon of paint covers approximately 350–400 square feet with a single coat according to most paint manufacturers. To calculate wall area: multiply the room perimeter by wall height, then subtract window and door areas. A standard interior door is about 21 sq ft, and a standard window is about 15 sq ft.
Wall Area Formula
Wall area = (2 × length + 2 × width) × ceiling height − doors − windows. For a 12×15 room with 8-foot ceilings, one door, and two windows: (2×12 + 2×15) × 8 − 21 − 30 = 432 − 51 = 381 sq ft. That's about 1 gallon for one coat, or 2 gallons for two coats.
Area Unit Conversions
| From | To | Multiply By |
|---|---|---|
| Square feet | Square meters | 0.0929 |
| Square meters | Square feet | 10.764 |
| Square feet | Square yards | 0.1111 |
| Square feet | Acres | 0.0000229568 |
| Acres | Square feet | 43,560 |
Step-by-Step Instructions
- 1Select the shape of the area you want to measure (rectangle, triangle, circle, etc.).
- 2Enter the dimensions (length, width, radius, etc.) in feet or meters.
- 3Add additional rooms or shapes to calculate total project area.
- 4View the total square footage and unit conversions.
- 5Use the materials estimator for flooring or paint coverage.
- 6Adjust the waste factor for your specific project needs.