Square Footage Calculator
Add or subtract rectangular, circular, triangular, and trapezoidal areas with flexible measurement units.
How to use the square footage calculator
- Measure the actual project. Break irregular work into separate sections and record finished dimensions consistently.
- Enter the core measurements. The quick view focuses on project geometry; add or subtract sections where the calculator supports multiple areas.
- Review purchasing assumptions. Open Advanced inputs to replace example prices, waste, coverage, density, pack size, minimum order, or delivery assumptions with current project information.
- Calculate and verify. Review the formula, limitations, whole-unit rounding, product instructions, and supplier requirements before purchasing.
Key inputs covered: Optional example price, Area operation, Shape, Length, Width, Border width, Radius / outer radius, Base, Top width, Perpendicular height, and additional project-specific assumptions.
Result coverage: The square footage calculator reports 5 separate quantities so the primary estimate and its supporting purchase or planning values can be checked together.
Find total square footage across multiple areas
Combine rooms, outdoor areas, and deductions in one estimate. Choose a shape for each area, enter its measurements, and subtract openings or excluded zones when needed.
Multiple rooms and deductions
Add each room as its own row and use subtract rows for excluded areas. This preserves a transparent breakdown instead of requiring one combined length and width.
Irregular and curved shapes
Circles, rings, sectors, triangles, parallelograms, and trapezoids help approximate spaces that are not simple rectangles. Split complex plans into smaller measurable shapes.
Common area conversions
Use one measurement system consistently. These factors convert a completed area total rather than individual length measurements.
| Starting area | Equivalent square feet |
|---|---|
| 1 square inch | 0.006944 ft² |
| 1 square yard | 9 ft² |
| 1 square meter | 10.7639 ft² |
| 1 acre | 43,560 ft² |
Planning note: Conversions follow the unit relationships published in the NIST Handbook 44 unit tables. Retain unrounded values until the final result.
How the estimate works
Net area is the sum of added shapes minus subtracted shapes. Each shape quantity is applied before totaling.
A 15 ft × 12 ft rectangle contains 180 ft², or 20 yd².
Assumptions, rounding, and limitations
Dimensions are treated as finished measurements. Only deductions and allowances entered above are included. Decimal measurements display to two places; purchase quantities round up when a whole container or piece is required.
- Use subtract areas for openings or excluded zones.
- Shared edges can make the summed perimeter larger than the actual outside boundary.
- Measure different rooms as separate rows.
Sources and review
These references support unit conversions and selected planning assumptions. Product instructions and local requirements control the actual project.
Last reviewed: 2026-10-09
Editorial process
BuildPlanCalc publishes the formula, editable assumptions, limitations, and supporting references so the estimate can be checked rather than treated as a black box. See the calculation and review methodology, or report a correction.
Frequently asked questions
Are the results exact?
No. Results are planning estimates based on the dimensions and assumptions entered. Confirm product coverage, site conditions, and ordering rules with the supplier.
How do I calculate square footage for an irregular room?
Divide the room into simple shapes, add each shape as a separate area, and subtract any openings or missing sections.