To calculate square feet, measure the dimensions of a surface in the same unit, apply the correct area formula and convert the result to square feet. Use this calculator for rectangles, triangles, circles, L-shaped spaces or a known area, then review material allowance and package estimates separately from measured area.
Square Feet and Area Calculator
Select a shape, enter its measurements and get square footage with common area conversions.
What Is a Square Foot?
A square foot is an area equal to a square measuring 1 foot by 1 foot. Square footage measures a two-dimensional surface, such as a floor, wall, ceiling, countertop or parcel. It is different from linear feet, which measure length, and cubic feet, which measure volume.
1 square foot = 12 in × 12 in = 144 square inches
1 square foot = 0.09290304 square metre
How to Calculate Square Feet for a Rectangle
Measure length and width, convert both measurements to feet, then multiply them. A 12-foot by 10-foot room contains 120 square feet.
Square feet = length in feet × width in feet
Mixed-unit example: If one side is 12 feet and the other is 90 inches, convert 90 inches to 7.5 feet before multiplying. The area is 90 square feet.
Square Footage Formulas by Shape
For a circle measured by diameter, divide the diameter by 2 to get the radius. For a triangle, use the perpendicular height rather than the sloping side.
How to Calculate an L-Shaped or Irregular Room
Break a complex floor plan into simple rectangles, calculate each area and add the results. For an L-shaped space, another method is to calculate the full outer rectangle and subtract the missing rectangular cutout.
L-shaped area = outer rectangle area − cutout area
For curved or highly irregular boundaries, divide the space into smaller measurable shapes or use a scaled drawing, survey or professional measurement service.
How to Calculate Wall Square Footage
- Measure each wall's width and height.
- Multiply width by height for each wall.
- Add all wall areas.
- Calculate door and window areas separately.
- Subtract openings only if the product or contractor's measurement method requires it.
Paint, tile, wallpaper and panel products have different coverage and waste rules. A measured wall area is the starting point, not always the final order quantity.
Square Feet Conversion Table
| Starting area | Equivalent square feet | Conversion method |
|---|---|---|
| 1 square inch | 0.006944 ft² | Divide square inches by 144 |
| 1 square yard | 9 ft² | Multiply square yards by 9 |
| 1 square metre | 10.763910 ft² | Divide square metres by 0.09290304 |
| 1 acre | 43,560 ft² | Multiply acres by 43,560 |
| 1 hectare | 107,639.104 ft² | Multiply hectares by approximately 107,639.104 |
Do not convert area as though it were length. Because 1 foot equals 12 inches, 1 square foot equals 12 squared, or 144 square inches.
Square Footage Calculation Example
12 ft × 10 ft rectangular room
Keep the 120-square-foot measured area separate from the 132-square-foot material-planning quantity.
How to Measure Multiple Rooms
Calculate each room or section separately, then add the individual square-foot results. Keep a simple measurement list so closets, halls, alcoves and repeated spaces are not omitted or counted twice.
Total square footage = area 1 + area 2 + area 3 + …
Published home area may follow appraisal, tax, leasing or building-measurement conventions that differ from a do-it-yourself floor measurement.
Measurement Tips for Better Results
- Use the same unit for every dimension before multiplying.
- Measure finished surfaces when estimating finished coverage.
- Record dimensions immediately and label each room or section.
- Measure at more than one point when walls are not parallel.
- Avoid rounding intermediate values; round the final result.
- Confirm whether openings, columns, cabinets or unusable areas should be deducted.
- Verify package coverage and required installation allowance with the manufacturer.
Related Calculators and Measurement Sources
Use the cubic feet calculator when height or depth makes the problem three-dimensional. Estimate landscaping material with the gravel calculator, browse the Global Calculators directory, or explore more free calculators and money tools from 1Dollars.
Area definitions and conversion methodology were reviewed against the NIST SI Units – Area guide, NIST area calculation guidance and NIST SP 811 conversion factors.
Methodology reviewed: July 19, 2026
How to Calculate Square Feet FAQs
How do you calculate square feet?
Convert length and width to feet, then multiply them. For example, 12 feet multiplied by 10 feet equals 120 square feet.
How many square feet is a 12 × 12 room?
A 12-foot by 12-foot room is 144 square feet because 12 multiplied by 12 equals 144.
How do I calculate square feet from inches?
Multiply length by width in inches to get square inches, then divide by 144. Alternatively, divide each linear measurement by 12 before multiplying.
How do I calculate square feet for an irregular room?
Divide the room into rectangles, triangles or other simple shapes, calculate each area and add them. For an L-shape, subtract the cutout from the full outer rectangle.
How do I calculate wall square footage?
Multiply each wall's width by its height and add the wall areas. Subtract doors and windows only when the project measurement method calls for those deductions.
How many square feet are in a square yard?
One square yard equals 9 square feet because a yard is 3 feet and 3 feet multiplied by 3 feet equals 9 square feet.
How many square feet are in an acre?
One acre contains 43,560 square feet.
How do I convert square metres to square feet?
Divide square metres by 0.09290304, or multiply by approximately 10.7639104.
Should I add extra square feet for flooring?
Many installations need an allowance for cuts, pattern matching, breakage or future repairs, but the percentage varies. Follow the product and installer's guidance.
Is square footage the same as cubic footage?
No. Square footage measures two-dimensional area. Cubic footage measures three-dimensional volume and includes length, width and height or depth.
Measurement notice: This calculator provides geometric estimates. Contracts, appraisals, permits, property listings and material orders may require a defined measurement standard or professional verification.