Square Footage Calculator
Calculate area for any common shape. Output in square feet, square meters, acres, hectares — plus optional cost estimate.
Area
Area formulas — the basics
- Rectangle: length × width
- Square: side × side (or side²)
- Triangle: (base × height) ÷ 2
- Circle: π × radius²
- Trapezoid: ((base₁ + base₂) ÷ 2) × height
- Parallelogram: base × height (where height is perpendicular)
- Ellipse: π × radius₁ × radius₂
For irregular shapes, decompose into combinations of these. A T-shaped room is two rectangles. A pentagon is a triangle plus a rectangle. Everything reduces to basic shapes.
Unit conversions for area
- 1 ft² ≈ 0.0929 m²
- 1 m² ≈ 10.764 ft²
- 1 yd² = 9 ft² ≈ 0.836 m²
- 1 acre = 43,560 ft² ≈ 4,047 m² ≈ 0.405 hectare
- 1 hectare = 10,000 m² ≈ 2.47 acres
- 1 km² = 100 hectares ≈ 247 acres
- 1 mile² = 640 acres ≈ 2.59 km²
Real estate square footage standards
US real estate uses the ANSI Z765 standard for measuring single-family home square footage. Key rules:
- Measured from the exterior of exterior walls.
- Only finished, heated/cooled spaces count.
- Ceilings must be at least 7 feet (5 feet under sloped ceilings, with 50%+ at full 7').
- Garages, unfinished basements, and uninsulated attics are NOT included.
- Finished basements are usually listed separately as “below-grade” square footage.
- Stairs count as part of both floors they serve.
Listing agents sometimes inflate “total” or “living” square footage by including spaces ANSI excludes. When comparing homes, ask for ANSI-compliant measurements or hire an appraiser if buying.
Common use cases
Flooring
Calculate the room area, add 5–10% waste factor for cuts and pattern matching. Hardwood: 7–10% waste. Tile (especially diagonal layouts): 10–15%. Carpet: 5–10%. Don't forget closets and hallways.
Paint
Walls: perimeter × ceiling height = wall area. Subtract doors (~21 ft² each) and windows (~15 ft² each). One gallon covers ~350 ft² with two coats. Use our Paint Calculator for the full math.
Lawn / sod
Sod is sold by square footage or by pallet (~450 ft² per pallet typically). Measure each lawn section separately, sum, add 5% waste for trimming.
HVAC sizing
Square footage is one input for HVAC capacity (Manual J calculation). Rough rule: 1 ton AC per 500–600 ft² in moderate climates, more in hot/humid areas. But this varies dramatically with insulation, windows, ceiling height, and orientation — always have an HVAC pro do a Manual J for a real install.
Tips for measuring
- Use a laser distance measure — $30 hardware-store tools are accurate to ¼ inch over 50 feet. Faster and more accurate than a tape measure for room measurements.
- Measure twice — small errors at one wall multiply across the room.
- Sketch the shape before measuring — helps you catch missed corners and double-count zones.
- Watch for closet spaces — easy to miss when measuring living areas.
- Round consistently — measure to nearest inch or 0.1 ft, don't mix.
- For very irregular spaces — divide and conquer. Mark sections, measure each.
Pair this with our Paint Calculator for room painting, the Concrete Calculator for slabs and patios, and the Unit Converter for any conversions.