Square Footage Calculator
Calculate the square footage of rooms, walls, and surfaces for accurate construction estimates.
Formula
Square Footage = Length (ft) × Width (ft). For walls: Height × Width. For triangles: (Base × Height) / 2. For circles: π × Radius²
How to Use
- 1Measure the length and width of each rectangular area in feet (convert inches to decimal feet by dividing by 12).
- 2Multiply length by width for each rectangular section.
- 3For wall area, multiply wall height by wall length for each wall, then subtract window and door openings.
- 4Break irregular rooms into rectangles, triangles, and circles, calculate each section, and add them together.
- 5Record all measurements and calculations to support your estimate and catch errors.
Example
Scenario
You need to calculate the total wall area for a 14×16 foot room with 9-foot ceilings, one 3×5 foot window, and one 3×7 foot door.
Calculation
Room perimeter: (14 + 16) × 2 = 60 linear feet. Total wall area: 60 × 9 = 540 sq ft. Window opening: 3 × 5 = 15 sq ft. Door opening: 3 × 7 = 21 sq ft. Net wall area: 540 - 15 - 21 = 504 sq ft.
Result
The paintable wall area is 504 square feet. For drywall, you would also need 224 square feet for the ceiling (14 × 16).
Tips
- Always measure actual dimensions on site — plans and blueprints may not match as-built conditions, especially in older homes.
- Convert all measurements to feet before multiplying (6 inches = 0.5 feet, 3 inches = 0.25 feet).
- For estimating purposes, some contractors do not subtract small openings (under 20 sq ft) since the extra material covers waste and cutting.
- Sketch each room with dimensions as you measure — this creates a record you can reference when building the estimate.
Estimate the Whole Job
ContractorIQ builds an itemized estimate of materials and labor from a photo or a description of the job.
FAQs
Common questions about the square footage calculator
Break the room into simple shapes: rectangles, triangles, and partial circles. Calculate the area of each shape separately (length × width for rectangles, base × height / 2 for triangles, π × r² for circles). Add all the areas together for the total square footage. For L-shaped rooms, divide into two rectangles.
For painting and drywall estimates, subtract all openings larger than about 20 square feet. Many contractors leave in smaller openings as a built-in waste allowance. For siding and exterior work, subtract all openings since material costs are higher and accuracy matters more.
Measure the footprint of the roof from the ground (length × width), then multiply by a pitch factor to account for the slope. A 4/12 pitch uses a factor of 1.054, 6/12 uses 1.118, 8/12 uses 1.202, and 12/12 uses 1.414. For example, a 30×40 foot footprint (1,200 sq ft) with a 6/12 pitch = 1,200 × 1.118 = 1,342 actual square feet of roof surface.