Free square footage calculator
Find the exact square footage of any room shape — rectangle, triangle, circle, or trapezoid — so you can order the right amount of flooring, tile, or paint without guesswork.
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Area unit² matches input units. Enter feet for sq ft, meters for m².
Results are estimates. Consult a professional.
How the square footage calculator works
Square footage is a two-dimensional measurement of surface area. You pick a shape, enter its dimensions in feet, and the calculator applies the matching geometric formula to give you the area in square feet. For rooms that are not a simple rectangle — a bay window alcove, a triangular corner, a curved rotunda — choose the shape that best fits that section, calculate each part separately, then add them up.
Worked example: measuring a 12 × 15 ft bedroom
Marcus is flooring a 12 × 15 ft bedroom and needs to know how many square feet of hardwood to order. He measures the longest wall (15 ft) and the adjacent wall (12 ft) and enters both into the rectangle mode.
Area = length × width = 15 × 12 = 180 square feet. Adding a standard 10% waste factor for cuts and offcuts brings the order to 198 sq ft — so Marcus rounds up to 200 sq ft when he visits the flooring store.
Square footage for common room sizes and shapes
Use this table for a quick ballpark before you measure. All figures are exact to the formula; round up when ordering materials to avoid falling short.
| Shape | Dimensions | Area (sq ft) |
|---|---|---|
| Rectangle | 10 ft × 12 ft | 120 |
| Rectangle | 12 ft × 15 ft | 180 |
| Rectangle | 20 ft × 25 ft | 500 |
| Triangle | base 16 ft, height 10 ft | 80 |
| Circle | radius 5 ft (dia. 10 ft) | 78.54 |
| Circle | radius 10 ft (dia. 20 ft) | 314.16 |
| Trapezoid | sides 8 ft & 12 ft, height 9 ft | 90 |
Rectangle = length × width; triangle = ½ × base × height; circle = π × radius²; trapezoid = ½ × (a + b) × height. Circle values rounded to 2 decimal places.
When to use it and how to measure correctly
Square footage drives material orders for flooring, tile, carpet, paint and wallpaper, as well as listing areas for real-estate valuations. Measuring accurately before you order avoids costly returns or short shipments.
- Measure each room separately. Add the results at the end rather than treating the whole floor as one shape — odd angles and closets add up.
- For irregular rooms, break them into sub-shapes. An L-shaped living room splits cleanly into two rectangles; a bay alcove might be a small rectangle or semicircle added on.
- Add a waste margin when ordering materials. Flooring and tile installers typically add 5–10% for cuts; carpet adds 10–15% for seaming and pattern matching.
- Use interior dimensions for flooring, exterior for painting. Walls are measured exterior-face to exterior-face for paint coverage, but floor area uses the inside measurement only.
How accurate is this square footage calculator?
The formula math is exact. Rectangle, triangle, circle and trapezoid formulas are standard Euclidean geometry — given correct inputs the results are precise to as many decimal places as shown. The circle formula uses π to full floating-point precision; rounding only occurs in what is displayed.
Accuracy in practice depends on your measurements. Rooms are rarely perfectly square — walls bow slightly, corners are not exactly 90° and tape measures flex over long spans. For flooring or tile work, always verify measurements on-site with a quality tape measure. This calculator gives you the planning figure; a licensed contractor will take their own site measurements before ordering materials for a major project. For real-estate square-footage reporting, ANSI Z765-2021 sets the standard method for measuring residential buildings — consult a certified appraiser when official figures are required.
Square footage terms defined
About this square footage calculator
This calculator runs entirely in your browser — your measurements are never sent to a server, stored, or shared with anyone. It works offline once the page has loaded, so you can use it on a job site without a reliable connection.
Need a related result? Pair this with our cubic feet calculator for volume, or head to home & garden calculators to browse all tools. You can also explore our full library of free calculators.