Square Footage Calculator
Enter your measurements in whatever units you took them in — feet, inches, yards or meters — and get the area in square feet, along with square yards, square meters and acres. Pick a shape for L-shaped rooms, circles and triangles, and add extra areas to total up a whole house.
Results
How to calculate square footage
Square footage is just length times width once both are in feet. The only thing that trips people up is that measurements rarely arrive in feet — a tape gives you 14 ft 6 in, a plan gives you meters, a lot listing gives you yards. Convert first, multiply second. The calculator does the converting for you; the formulas underneath are these:
| Shape | Formula | Example |
|---|---|---|
| Rectangle or square | length × width | 20 × 15 ft = 300 sq ft |
| L-shaped room | (overall length × overall width) − (cut-out length × cut-out width) | 20 × 15 − 8 × 6 = 252 sq ft |
| Circle | π × (diameter ÷ 2)² | 12 ft across = 113 sq ft |
| Triangle | base × height ÷ 2 | 18 × 10 ÷ 2 = 90 sq ft |
For a whole house or a yard made of several sections, work out each rectangle separately and add them up — that is what the Add another area button does. Breaking an awkward space into two or three rectangles is almost always faster and more accurate than trying to find one clever formula for the whole thing.
Converting to other units
Bulk suppliers, flooring boxes and lot listings all use different units for the same area. These are the conversions the calculator applies:
| Unit | Conversion |
|---|---|
| Square inches | 1 sq ft = 144 sq in |
| Square yards | 1 sq yd = 9 sq ft — divide sq ft by 9 |
| Square meters | 1 sq ft = 0.0929 sq m — divide sq ft by 10.764 |
| Acres | 1 acre = 43,560 sq ft |
Watch the squaring when you convert lengths. A yard is 3 feet, but a square yard is nine square feet, because both sides tripled. The same trap catches meters: 1 m is 3.28 ft, so 1 sq m is 3.28² = 10.76 sq ft. Converting the length measurements before multiplying, as this calculator does, avoids the mistake entirely.
Measuring a real room accurately
- Measure at floor level, not at waist height — baseboards, bay windows and out-of-plumb walls all make the mid-wall figure wrong.
- Take each wall twice if the room looks square but might not be. Older houses are routinely an inch or two out over 15 feet, which is a couple of square feet either way.
- Round up to the nearest inch, not down. Under-measuring costs a second delivery; over-measuring costs a few dollars.
- Closets, alcoves and door swings count if you are flooring them and do not if you are not. Decide once, before you measure, and stay consistent.
- Sloped ceilings and stairs are not covered here — measure the floor they sit over, then handle the slope separately.
Square footage is not the order quantity
Almost nothing is ordered at exactly the square footage you measured. Flooring is sold in boxes and needs about 10% extra for cuts; sod comes in rolls and pallets; gravel and mulch are sold by volume, so the area has to be multiplied by a depth before it means anything. Work out the area here first, then take it to the material calculator that matches your project — each one applies the waste factor and the packaging unit that product actually uses.
Frequently asked questions
How do I calculate square footage?
Measure the length and the width in feet and multiply them. A room 20 feet by 15 feet is 300 square feet. If your measurements are in inches, divide by 12 first; if they are in meters, multiply by 3.28 first. For rooms that are not simple rectangles, split the space into rectangles, work out each one, and add the results together.
How many square feet is a 20x15 room?
A 20 by 15 foot room is 300 square feet (20 × 15 = 300). That is the same as 33.33 square yards or 27.87 square meters. At 10% waste you would order flooring for about 330 square feet.
How do I find the square footage of an L-shaped room?
Measure the overall rectangle as if the missing corner were filled in, then measure the missing corner itself and subtract it. A 20 × 15 ft room with an 8 × 6 ft corner missing is 300 − 48 = 252 square feet. The L-shape option on this calculator does that subtraction for you.
How many square feet are in an acre?
An acre is 43,560 square feet. A square acre is roughly 209 feet on each side. This calculator shows the acreage automatically once the area passes 0.01 acres, which is about 436 square feet.
What is the difference between square feet and linear feet?
Square feet measure area — a surface, needing two dimensions. Linear feet measure length along a single line, so only one dimension. Flooring and paint are sold by area; baseboard, fencing and gutters are sold by linear foot. They are not interchangeable, and no conversion exists between them without knowing a width.
How do I calculate the square footage of a house?
Measure each room separately, then add the results. Use the Add another area button to keep a running total rather than writing figures on paper. Conventionally, finished heated space counts and garages, unfinished basements and open porches do not — though appraisers and local listing rules vary, so check which standard you need to match.