Enter your length and width below and this square footage calculator does the math for you, down to the inch. Use it for flooring, paint, rugs, rent comparisons, or any project where guessing gets expensive.
Square Footage Calculator
Pick the shape of your space, add a few measurements, and we will handle the math.
- Shape
- Measure
- Results
What shape is your space?
The closest match is fine. Odd layout? Split it into simple shapes and add them one at a time.
Add your measurements
Your areas
Waste allowance
Pros usually order 5 to 15 percent extra to cover cuts, breakage and pattern matching.
Order about 0 sq ft
Cost estimate
Results are estimates based on the measurements you enter. Always confirm quantities with your installer or supplier before ordering.
How Do You Calculate Square Footage?
Multiply length by width. A room that measures 12 feet by 10 feet is 120 square feet, because 12 × 10 = 120. That single formula, length × width, covers any rectangular space, which is most rooms, walls, decks, and yards you will ever measure.
The logic is simpler than it sounds. A square foot is literally a 12-inch by 12-inch square, so when you multiply the two sides of a room, you’re counting how many of those squares would fit on the floor.
Say your bedroom measures 14 feet along one wall and 11 feet along the other. 14 × 11 = 154 square feet. That’s the number you take to the carpet store.
Measuring a Room Without Messing It Up
The calculator can’t fix a bad measurement. Use a steel tape, not the floppy one from the sewing kit, and run it along the floor at the baseboard, because walls lean and eyeballed mid-air measurements drift.
Measure each wall at both ends. Older houses are almost never perfectly square, and when the two readings disagree, keep the larger one. I’ve had to re-buy quarter round over a half-inch I decided didn’t matter.
If you’re doing floors, measure into closets, doorways, and bay window nooks too. They feel small until you’re three boxes short on a Sunday evening.
What About Feet and Inches?
Tape measures don’t say 12.5 feet. They say 12 feet 6 inches, and the fix is to divide the inches by 12 before you multiply. So 6 inches becomes 0.5, 3 inches becomes 0.25, and 9 inches becomes 0.75.
A room that’s 12’6″ by 10’3″ works out as 12.5 × 10.25 = 128.1 square feet. For small areas it’s easier to stay in inches: multiply the two sides, then divide by 144, since one square foot holds 144 square inches. A 30 × 48 inch hearth is 1,440 square inches, or exactly 10 square feet.
Rooms That Aren’t Rectangles
An L-shaped room is just two rectangles wearing a trench coat. Split it at the corner, calculate each piece, and add them. A living room that’s 15 × 12 on the main section with a 6 × 8 dining nook is 180 + 48 = 228 square feet.
For a triangle, multiply base by height and cut it in half. For a circle, multiply 3.14 by the radius squared, where the radius is half the distance across. Genuinely odd rooms break down the same way: carve out the biggest rectangles you can and treat the leftover slivers as triangles.
Square Footage for Flooring and Paint
The number you measured is rarely the number you buy. Flooring installers add 5 to 10 percent for cuts and waste, and closer to 15 percent for diagonal lays, herringbone, or patterned tile that needs matching. Carpet also comes on 12-foot rolls, so a 13-foot-wide room means a seam and more waste than the raw math suggests.
Walls flip the formula on its side. Add up the perimeter of the room, multiply by ceiling height, then subtract about 20 square feet per door and 15 per window. One gallon of paint covers roughly 350 to 400 square feet per coat.
Price per square foot runs in reverse: divide total cost by area. A $1,200 quote on a 240 square foot floor is $5 per square foot, which is the only honest way to compare two bids.
How House Square Footage Is Measured
Room math and listing math are not the same thing. US listings generally follow the ANSI Z765 standard, which counts finished, heated, above-grade space and measures from the outside of the exterior walls. Garages, porches, and unfinished basements stay out of the total, and finished basements are usually listed separately.
Ceiling height matters too. Sloped attic rooms only count where the ceiling clears five feet, and at least half of the space needs seven. This is also why your room-by-room tape total never quite matches the listing: exterior measurement quietly adds the thickness of every wall.
Common Room Sizes in Square Feet
If your room is a standard size, skip the square foot calculator entirely. The math is already done.
| Dimensions | Square feet | Typical space |
|---|---|---|
| 8 × 10 | 80 | Home office or nursery |
| 10 × 10 | 100 | Small bedroom |
| 10 × 12 | 120 | Kids’ bedroom |
| 12 × 12 | 144 | Standard bedroom |
| 12 × 16 | 192 | Primary bedroom |
| 15 × 20 | 300 | Living room |
| 20 × 20 | 400 | Two-car garage |
How many square feet is a 12×12 room?
A 12×12 room is 144 square feet, because 12 × 12 = 144. If you’re buying flooring for it, order around 158 square feet so the standard 10 percent waste factor doesn’t leave you one box short of finishing.
Can you convert square feet back to feet?
Not directly. Square feet measure area and feet measure length, so a 100 square foot space could be 10 × 10 or 5 × 20. If the space is a perfect square, take the square root: a 144 square foot room runs 12 feet per side.
Do closets count in square footage?
Yes, when they’re finished and heated. Listings include closets in a home’s total, and you should include them when ordering wall-to-wall flooring. Leave them out only when the job stops at the closet door, like an area rug or a quick paint estimate.