Add up the area of one or two rectangular spaces, subtract any cut-outs, and see square feet, square yards and square meters.
How to calculate square footage
For a rectangular surface, multiply length by width in feet. A 12 x 10-foot room is 120 square feet. For two spaces, add their rectangular areas and subtract only the area you will not cover. Our default example is 20 x 15 plus 10 x 8 minus 20 = 360 square feet, 40 square yards or 33.45 square meters.
Net square feet = length 1 x width 1 + length 2 x width 2 - excluded area.
Square yards = square feet / 9.
Square meters = square feet x 0.09290304. A rectangle's length-times-width formula is documented by Math Is Fun and Calculator.net.1, 2 Unit conversions follow squared length factors: 3 feet per yard gives 9 square feet per square yard.
Room size chart
Our calculated chart assumes one full rectangle without deductions or waste. These are example room sizes, not estimates of your room.
| Length x width | Square feet | Square yards | Square meters |
|---|---|---|---|
| 8 x 10 feet | 80 | 8.89 | 7.43 |
| 10 x 10 feet | 100 | 11.11 | 9.29 |
| 10 x 12 feet | 120 | 13.33 | 11.15 |
| 12 x 12 feet | 144 | 16.00 | 13.38 |
| 12 x 15 feet | 180 | 20.00 | 16.72 |
| 15 x 20 feet | 300 | 33.33 | 27.87 |
| 20 x 20 feet | 400 | 44.44 | 37.16 |
Three checked examples
1. Two spaces with a cut-out
Space 1 is 20 x 15 = 300 square feet. Space 2 is 10 x 8 = 80. Add: 300 + 80 = 380. An excluded 20-square-foot area leaves 360 square feet. Divide by 9: 40 square yards. Multiply by 0.09290304: 33.4450944, displayed as 33.45 square meters.
2. A room measured in feet and inches
A 12-foot-6-inch by 10-foot-3-inch room uses 12.5 by 10.25 feet. Its area is 12.5 x 10.25 = 128.125 square feet, or 14.2361111 square yards and 11.9032020 square meters. Enter 0 or leave both second-space fields blank. Do not enter 12.6 for 12 feet 6 inches: 6 / 12 is 0.5 foot.
3. An L-shaped floor
Split it into two nonoverlapping rectangles, for example 18 x 10 and 8 x 6 feet. Their areas are 180 and 48 square feet. Total: 228 square feet, or 25.33 square yards and 21.18 square meters. Leave subtraction at zero if the split already excludes the missing corner. Subtracting that corner again would undercount.
Measure the area you will cover
Measure each side rather than assuming a room is an exact rectangle. Keep the original measurements and convert inches to decimal feet using inches / 12. For instance, 9 feet 9 inches is 9.75 feet. Avoid rounding every measurement up before calculating; that can hide how much extra material you deliberately choose to buy.
A closet is not automatically a deduction. Include it if you will install flooring there. Subtract it only if the measured outer rectangle includes it and you will not cover it. Treat built-ins the same way. The form rejects a deduction equal to or larger than the total area so a mistaken cut-out does not produce a usable-looking quantity.
Irregular spaces and more than two rooms
Use nonoverlapping rectangles for an L-shaped area. For more than two rectangles, calculate groups and add their unrounded areas. Do not combine a full outer rectangle with an interior rectangle that it already contains. Calculator.net explains splitting complex areas into simple shapes and totaling them.2
This form does not have a circle or triangle input. For those, use the shape formulas in our irregular-yard measuring guide: triangle area is base x perpendicular height / 2, and circle area is pi x radius squared.1 The radius is half the diameter, not the full width. Curved boundaries may need several smaller measured sections rather than a bounding rectangle.
Square footage is not the purchase quantity
The result is net area, before waste or rounding to cartons, rolls, sheets or bags. Enter that net area in the relevant flooring calculator, tile calculator or sod calculator, then use the product's actual coverage and appropriate allowance there. Applying an allowance here and again in a material calculator would count it twice.
For paint, measure the walls or ceiling you will paint, not the floor area. For mulch, gravel or concrete, area alone is not volume: the chosen depth is also needed. A 100-square-foot patch at 2 inches deep uses a different volume than the same patch at 6 inches. This calculator does not choose a construction depth or a product coverage rate.
Metric mode
The site's unit switch converts feet dimensions to meters and the subtraction field to square meters. Equivalent metric inputs return the same physical area, with the original square-foot result available. The area-to-subtract input is an area, not a side length. Enter square meters there in metric mode, not meters.
FAQ
Is 12 x 12 equal to 144 square feet?
Yes, when both dimensions are feet. 12 x 12 = 144 square feet, 16 square yards or 13.38 square meters. A 12 x 12-inch tile is 1 square foot, not 144 square feet.
Can I leave the second space blank?
Yes. Leave both second-space dimensions blank or use zero for both. The form rejects a single positive dimension without its matching positive width or length. Negative optional inputs are rejected rather than silently treated as zero.
Is this suitable for listing a home's official square footage?
It calculates geometric areas, not a certified appraisal or property-listing measurement. It does not decide which spaces count under a measurement standard, and it does not account for wall thickness or listing rules. Use a qualified measurement when those distinctions matter.
Sources
- Math Is Fun: Area of Plane Shapes (rectangle, triangle and circle formulas)
- Calculator.net: Area Calculator (rectangular area and complex-shape decomposition)
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