How to Calculate Square Footage
To calculate square footage (sq ft), measure the length and width of a space in feet (ft), then multiply the two measurements together. The result is the area in square feet.
Basic Formula for Area
For a room that measures 15 feet (4.57 meters) long and 12 feet (3.66 meters) wide, the area is 180 square feet (16.72 square meters). Measure both dimensions in the same unit before multiplying. Convert inches (in) to feet by dividing by 12, since 1 foot equals 12 inches (30.48 centimeters).
Area Formulas for Different Shapes
Below are formulas for five of the most commonly used shapes. The calculator above also supports sectors, parallelograms, annuli and border shapes. Select a shape below to see the formula, diagram, and example calculation for each shape.
Square
A square shape with sides of 10 feet (3.05 meters) has an area of 100 square feet (9.29 square meters). All 4 sides of a square are equal in length.
Rectangle
A rectangle shape measuring 15 feet (4.57 m) long and 10 feet (3.05 m) wide has a rectangle area of 150 square feet (13.94 square meters). The rectangle area formula is the most commonly used formula in square footage calculations.
Circle
A circle shape with a diameter of 10 feet (3.05 meters) has a radius of 5 feet. The area of a circular shape is π × 5² = 78.54 square feet (7.30 square meters). Use this formula for round rooms, pools, and circular driveways.
Triangle
A triangle shape with a base of 12 feet (3.66 m) and a height of 8 feet (2.44 m) has an area of 48 square feet (4.46 sq m). Use this formula for triangular shapes in gable walls, roof sections, and angled corners.
Trapezoid
A trapezoid with a top base of 8 feet (2.44 m), a bottom base of 14 feet (4.27 m), and a height of 6 feet (1.83 m) has an area of 66 square feet (6.13 sq m). Use the trapezoid formula for cathedral walls, right trapezoid shapes, and sloped ceilings.
How to Figure Out the Square Footage of a Wall
To calculate the square footage of a wall, multiply the wall height by the wall width. Subtract the area of any windows or doors from the total wall area to get the net paintable or coverable surface.
Wall and Window Shape
A wall that measures 10 feet (3.05 m) wide and 8 feet (2.44 m) tall has 80 square feet (7.43 sq m) of total area. A window measuring 3 ft × 4 ft occupies 12 sq ft (1.11 sq m). The net wall area is 80 − 12 = 68 square feet (6.32 sq m). Subtract additional areas for doors, vents, and other openings when calculating square footage for drywall or painting a house.
How to Calculate the Square Footage of a House
To calculate the square footage of a house, measure the length and width of each room, calculate each room's area in square feet, then add all room areas together. The square footage of a house includes all finished, conditioned (heated and cooled) spaces measured from the exterior walls.
Bedrooms, living rooms, kitchens, bathrooms, and hallways count toward the total square footage of a house. Garages, unfinished basements, unfinished attics, and covered porches are excluded from the standard square footage in most real estate listings, excluding non-conditioned spaces from the total.
Usable square footage is the floor area a homeowner or tenant occupies directly. Usable square footage excludes shared areas such as lobbies, stairwells, and mechanical rooms. Usable square footage is always smaller than gross square footage in commercial real estate and multi-story additions.
Adding a Waste or Surplus Allowance for Materials
Add a surplus percentage to the calculated square footage before purchasing materials for flooring installation, painting a house, or drywall work. The surplus accounts for cuts, waste, mistakes, and pattern matching during installation. Most contractors recommend adding 10% surplus for standard materials.
Waste Percentages by Material Type
| Material Type | Waste Percentage | Multiply Area By |
|---|---|---|
| Standard Flooring (vinyl, laminate) | 5–10% | × 1.10 |
| Diagonal / Herringbone Pattern | 10–15% | × 1.15 |
| Complex Tile Patterns | 15–20% | × 1.20 |
| Hardwood Flooring | 5–10% | × 1.10 |
| Carpet | 5–10% | × 1.10 |
| Drywall | 10–15% | × 1.15 |
| Painting (coverage) | 5–10% | × 1.10 |
Basic Length Conversion
Use the table below to convert between common length units when measuring square footage. Convert all dimensions to the same unit before multiplying length by width.
| From | To | Multiply By | Example |
|---|---|---|---|
| Feet (ft) | Inches (in) | × 12 | 10 ft = 120 in |
| Inches (in) | Feet (ft) | ÷ 12 | 36 in = 3 ft |
| Feet (ft) | Meters (m) | × 0.3048 | 10 ft = 3.048 m |
| Meters (m) | Feet (ft) | × 3.2808 | 3 m = 9.84 ft |
| Feet (ft) | Centimeters (cm) | × 30.48 | 5 ft = 152.4 cm |
| Feet (ft) | Yards (yd) | ÷ 3 | 12 ft = 4 yd |
| Yards (yd) | Feet (ft) | × 3 | 5 yd = 15 ft |
| Meters (m) | Centimeters (cm) | × 100 | 2.5 m = 250 cm |
| Inches (in) | Millimeters (mm) | × 25.4 | 6 in = 152.4 mm |
Area Conversion
Use the table below to convert between common area units. These conversions are used during renovation planning, commercial real estate audits, and HVAC sizing for multi-story additions.
| From | To | Multiply By | Example |
|---|---|---|---|
| Square Feet (sq ft) | Square Meters (sq m) | × 0.0929 | 500 sq ft = 46.45 sq m |
| Square Meters (sq m) | Square Feet (sq ft) | × 10.764 | 50 sq m = 538.2 sq ft |
| Square Feet (sq ft) | Square Yards (sq yd) | ÷ 9 | 1,800 sq ft = 200 sq yd |
| Square Feet (sq ft) | Acres | ÷ 43,560 | 43,560 sq ft = 1 acre |
| Acres | Square Feet (sq ft) | × 43,560 | 0.5 acre = 21,780 sq ft |
| Square Inches (sq in) | Square Feet (sq ft) | ÷ 144 | 1,728 sq in = 12 sq ft |
| Square Meters (sq m) | Square Centimeters | × 10,000 | 1 sq m = 10,000 sq cm |
| Acres | Square Meters (sq m) | × 4,046.86 | 1 acre = 4,046.86 sq m |
Specialty & Area Calculators
Explore our specialized calculators for specific room types, materials estimation, and complex geometric shapes.
Flooring Calculator
Calculate square footage for wood, laminate, or vinyl floors with automatic 10% waste calculation.
Paint Calculator
Estimate paint gallons needed based on wall square footage and coverage per gallon.
Tile Calculator
Determine the number of tiles required for floors or walls, accounting for gap size and waste.
Drywall Calculator
Calculate standard 4x8 or 4x12 drywall sheets needed for room walls and ceilings.
Annulus Area
Calculate the area of a ring or donut shape using outer and inner radii measurements.
Sector Area
Calculate the area of a circle sector (pie wedge) using radius and angle in degrees.
Parallelogram Area
Compute the area of a slanted parallelogram using base length and vertical height.
Triangle Area
Calculate triangle area using base and height, or three sides using Heron's formula.
Cathedral Wall
Calculate the square footage of walls with a peaked gable roof design (triangular top + rectangular bottom).
Sq Ft to Sq Meters
Convert area measurements between imperial square feet and metric square meters instantly.