MEASURE YOUR SPACE. PLAN YOUR NEXT STEP.
Square Footage Calculator
From a single room to your next outdoor project. Calculate area, combine spaces, and get the numbers you need to plan with confidence.
with the right numbers.
Your measurements
Enter your measurements to get started.
Example measurements are filled in. Adjust them for your project.
SOURCED REFERENCE FACTS
How do square-foot conversions work?
Square footage measures area. For a rectangle, multiply length by width after putting both measurements in the same unit. First calculate each non-overlapping shape, then add the areas, and finally convert the total if needed. The exact US customary conversions used here are documented by NIST Handbook 44 (2026): 1 square yard is 9 square feet, 1 acre is 43,560 square feet, and 1 square foot is 0.09290304 square meters. The examples below use unrounded intermediate values.
| Fact | Value | Source |
|---|---|---|
| 12 ft × 12 ft rectangle | 144 ft² | Answered example |
| 1 square yard | 9 ft² | NIST Handbook 44 (2026) |
| 1 acre | 43,560 ft² | NIST Handbook 44 (2026) |
| 1 square foot | 0.09290304 m² | NIST Handbook 44 (2026) |
| 300 square feet | 33.33 yd² or 27.87 m² | Exact conversions, rounded for display |
Direct answer: These figures use exact unit definitions and unrounded intermediate calculations. Displayed examples are rounded for readability; gravel density remains a material assumption that should be confirmed with a supplier.
THE SHORT ANSWER
How do you calculate
square footage?
For a rectangle, multiply length by width, with both measurements in feet. A 20 ft × 15 ft room has an area of 300 square feet. For an irregular space, calculate separate non-overlapping sections and add their areas.
01 / MEASURE ONCE. PLAN BETTER.
A few measurements. A clear answer.
Choose your shape
Use a rectangle for a room or square patio, a circle for a round bed, or a triangle for a corner. Split an L-shaped room into two rectangles without overlap.
Enter your measurements
Select the unit you measured in. For 12 feet 6 inches, enter 12.5 feet or 150 inches. Triangle height means the perpendicular distance from the base.
Plan your materials
Add more areas if needed. Optional extra material and a price per square foot help with an order estimate. The measured area is shown separately from the extra.
Square footage formulas
Square footage is the two-dimensional area inside a shape, expressed in square feet. Each formula needs dimensions in the same unit before calculation. A rectangle uses length and width; a circle uses its radius, which is half the entered diameter; and a triangle uses a base and the perpendicular height. Measurements in feet produce square feet. These geometry formulas are separate from the NIST Handbook 44 (2026) unit conversions used to display square meters, square yards, and acres.
| Shape | Area formula |
|---|---|
| Rectangle / square | length × width |
| Circle | π × (diameter ÷ 2)² |
| Triangle | base × height ÷ 2 |
The circle formula uses diameter, not radius. The calculator uses the full value of π internally and rounds only the displayed result.
A room-sized example
A rectangular room measures 20 feet long and 15 feet wide. Here is how the estimate changes when you add extra material.
Measured area: 20 × 15 = 300 ft²
With an illustrative 10% extra: 300 × 1.10 = 330 ft²
At $2.50 per ft²: 330 × $2.50 = $825
The extra percentage is your choice. Follow the material manufacturer’s guidance for cuts, patterns, and waste.
Convert square feet to other area units
Square feet, square meters, and square yards describe the same area in different units. They do not include thickness.
| From square feet | Conversion | 300 ft² example |
|---|---|---|
| Square meters (m²) | ft² × 0.09290304 | 27.87 m² |
| Square yards (yd²) | ft² ÷ 9 | 33.33 yd² |
| Acres | ft² ÷ 43,560 | 0.00689 acres |
Need to fill that space with material? Add a depth using the cubic yard calculator. For stone coverage and weight, use the gravel calculator.
A LITTLE MORE CLARITY
Square footage, explained.
How many square feet is a 12 × 12 room?
A room that is 12 feet long and 12 feet wide has 144 square feet of floor area. If those dimensions are in meters or inches, select that unit first; “12 × 12” alone does not identify the area unit.
How do I calculate an L-shaped room?
Divide it into two non-overlapping rectangles. Calculate each rectangle and add the results. For example, sections of 10 × 12 ft and 6 × 8 ft total 120 + 48 = 168 ft². Use “Add another area” for each section.
Can I calculate wall area with this tool?
Yes. Enter wall width as one dimension and wall height as the other. Add multiple walls. Subtract the area of doors and windows separately if your material estimate requires it; this calculator does not automatically subtract openings.
Is square footage the same as linear feet?
No. Linear feet measure length; square feet measure area. To convert a length to area, you also need a width. For example, a 10-foot-long strip that is 2 feet wide covers 20 square feet.
Can I use this for a home’s official listed square footage?
This tool calculates geometric area. It does not apply appraisal, building-code, or real-estate measurement rules about finished space, ceiling height, stairs, garages, or exterior walls. Verify requirements with the relevant professional before using a result in a property listing.
Formula reference: our calculation methodology. Unit conversion basis: NIST Handbook 44 (2026), Appendix C. Examples are illustrative, not quotes or construction specifications. Updated August 31, 2026.