Square Footage Calculator
Calculate the square footage of a room, wall, yard or lot in seconds. Pick a shape, enter your measurements in feet and inches or metres, and get the area in square feet, square metres, square yards and acres at once — with the space drawn to scale beneath, which you can drag to change the measurements.
Live scale preview
The shape is drawn to scale and relabelled as you type.
An example to start from. Drag a handle or type a measurement and it becomes yours.
How to calculate square footage
Square footage is area measured in square feet, and for any rectangular space it is one multiplication: length × width = area. A room that measures 12 feet by 15 feet is 180 square feet. That is the whole of it — the difficulty is never the arithmetic, it is handling the parts of a real space that are not a clean rectangle, and keeping your units straight while you do it.
This square footage calculator handles both. Measure each part of the space, choose the shape that matches it, and it does the geometry — including the awkward ones, like a circular patio, a triangular attic corner or an L-shaped living room. Every result is computed in metric and converted from one table of factors, so the four units it shows always agree exactly.
Using a square footage calculator with feet and inches
Tape measures read in feet and inches, so this calculator does too: every measurement gets a feet box and an inches box, and the inches box takes fractions. A wall reading 12 ft 6 1/2 in is entered exactly as it reads — 12 and 6 1/2 — with no arithmetic in your head. Each field also carries its own unit picker for inches, yards, metres, centimetres or millimetres.
By hand, divide the inches by 12 to get a decimal fraction of a foot: 12 ft 6 in is 12.5 ft, and 8 ft 3 in is 8.25 ft. These are the conversions that come up most:
| Inches | Decimal feet | Example |
|---|---|---|
| 1 in | 0.0833 ft | 10 ft 1 in = 10.0833 ft |
| 2 in | 0.1667 ft | 10 ft 2 in = 10.1667 ft |
| 3 in | 0.25 ft | 10 ft 3 in = 10.25 ft |
| 4 in | 0.3333 ft | 10 ft 4 in = 10.3333 ft |
| 6 in | 0.5 ft | 10 ft 6 in = 10.5 ft |
| 8 in | 0.6667 ft | 10 ft 8 in = 10.6667 ft |
| 9 in | 0.75 ft | 10 ft 9 in = 10.75 ft |
| 10 in | 0.8333 ft | 10 ft 10 in = 10.8333 ft |
| 11 in | 0.9167 ft | 10 ft 11 in = 10.9167 ft |
Or measure everything in inches and divide by 144: 150 in × 180 in = 27,000 sq in ÷ 144 = 187.5 sq ft — the same answer the calculator gives for 12 ft 6 in by 15 ft. Changing one field's unit moves the others with it, so a metric tape costs one change rather than one per box, and the choice is remembered between visits.
A square footage calculator that draws the space to scale
Numbers on their own hide mistakes. Underneath the calculator is a live scale preview: a to-scale drawing of the space you have entered, sitting on a grid whose squares are a stated size, with every side labelled and the area printed inside the shape. It redraws on every keystroke, so a width typed as 120 ft instead of 12 ft is obvious immediately rather than at the tile counter three steps later. All nine shapes are drawn, not just rectangles — a circle, a sector, a trapezoid and an L-shape each get their real outline, with construction lines for the measurements that are not edges, such as a triangle's perpendicular height.
The drawing is an input, not a picture. Every dimension carries a handle you can drag to resize the shape, and the measurement boxes above follow as you drag. Dragging snaps to the natural step for the unit you are working in — the nearest inch in feet and inches, a quarter of a foot in feet, 5 cm in metres — and holding Shift drags freely for a value in between. The handles are reachable by keyboard as well: tab to one and the arrow keys move it a step at a time. The harder shapes behave properly too, so a triangle's corner can be dragged without producing a triangle that cannot exist, and a sector's radius and its angle are moved independently.
Two things make the preview more than a sanity check. Show something for scale overlays a familiar object at true size against your shape — a queen bed, a parking space, a sheet of plywood, a two-car garage, fourteen in all — and for a rectangular space it says how many of them fit. That answers "is 180 square feet actually big?" in a way the number cannot. The drawing also downloads as a PNG or an SVG, labelled and still to scale, to send to a contractor or paste into a quote.
Rooms and lots that are not rectangles
Almost any floor plan splits into simple shapes: an alcove adds a rectangle, a bay window adds a trapezoid, an angled corner subtracts a triangle. Measure each piece and add the results — which is what the multi-room total calculator is for. You can also sketch the space on the snap-to-grid canvas above and drag its corners to match.
Square footage calculators by space
The measurement is the same everywhere; what changes is which surfaces you count.
Room square footage calculator
Measure wall to wall at floor level rather than at counter height, and take the width at two or three points — walls in older houses are rarely parallel. Do not deduct for furniture, and deduct a kitchen island only when you are buying flooring. For a standard size without measuring, the room size lookup has 30 common dimensions from 8×10 to 30×40, each drawn to scale with its materials worked out.
House and total square footage calculator
A house total is the sum of its rooms plus hallways, stairs and closets. Measure room by room rather than measuring the whole footprint at once: an exterior measurement includes wall thickness that an interior total does not, which is the usual reason a homeowner's figure disagrees with the listing. If the number is going onto a listing or into an appraisal it needs to be gross living area, so use the GLA calculator, which applies the ANSI Z765 rules on finished basements, garages and stairwell openings.
Wall square footage calculator
Wall area is height × width per wall, added, then minus the openings. A 10 × 8 ft wall is 80 sq ft; take off about 21 sq ft per door and 15 per window. Painters skip the deduction under 100 sq ft of openings, because cutting in absorbs the difference — the paint calculator follows the same convention.
Roof square footage calculator
A roof is bigger than the building beneath it, because it slopes. Measure the footprint, then multiply by the pitch factor for the roof's rise over a 12-inch run. Roofing is ordered in squares of 100 sq ft.
| Pitch | Multiplier | 1,500 sq ft footprint becomes |
|---|---|---|
| 4/12 | × 1.054 | 1,581 sq ft (15.8 squares) |
| 6/12 | × 1.118 | 1,677 sq ft (16.8 squares) |
| 8/12 | × 1.202 | 1,803 sq ft (18.0 squares) |
| 10/12 | × 1.302 | 1,953 sq ft (19.5 squares) |
| 12/12 | × 1.414 | 2,121 sq ft (21.2 squares) |
Yard, lawn, pool and lot
Outdoor spaces usually need more than one shape. Take the whole lot as a rectangle, then subtract the house footprint, the driveway and the patio to get the lawn you are actually seeding — grass seed and fertiliser are sold by coverage, so an over-estimate is money burned. Pools work the same way: rectangular pools are length × width, round pools are π × radius², and a kidney shape is close enough to a rectangle plus a half-circle at each end for a cover. Above 43,560 sq ft, read the figure in acres.
Square footage calculators by material
Every material adds a waste factor — the offcuts and pattern repeats you pay for but never install — and every material is sold in a unit that is not a square foot.
- Tile. Add 10% for a straight lay, 15% for diagonal or herringbone, then round up to whole boxes — and buy the extra in the same order, because dye lots vary.
- Paint. A US gallon covers roughly 350–400 sq ft per coat on primed drywall, less on bare or textured surfaces. Assume two coats for any colour change.
- Concrete. Ordered by volume, not area: multiply the square footage by the slab thickness in feet (4 in = 0.333 ft), then divide by 27 for cubic yards. A 400 sq ft patio at 4 inches is about 4.9 cubic yards.
- Countertops. Measure each run as its own rectangle at the full slab depth, typically 25 in, and count the corner where two runs meet once, not twice.
- Flooring, carpet and hardwood. Sold by the box or the roll, so the material calculators round up to whole units after the waste factor rather than leaving you to do it at the counter.
Square feet converter: what your result becomes
Every calculation here is shown in four units at once, because the unit you need depends on who is asking. One square metre is 10.764 square feet. A square yard is 9 square feet, which is how carpet and topsoil are sold; an acre is 43,560 square feet, which is how land is sold; and roofers work in squares of 100 sq ft. Conversion is where errors creep in: 3 ft = 1 yd does not make 3 sq ft = 1 sq yd, because the factor gets squared along with the unit.
Where square footage figures usually go wrong
Four mistakes account for most bad numbers. Mixing units — one side in feet, the other in inches — is the biggest, and it lands twelve times out. Measuring to the wrong surface comes next: interior and exterior measurements differ by the thickness of every wall. Forgetting the waste factor leaves you a box short on the last afternoon of a tiling job. And rounding too early compounds — keep the decimals until the final figure, then round once.
Every shape this calculator supports
Each shape has its own page with the formula, a worked example and the questions people ask:
The full index — by shape, by job and by material — is on the calculators page, and the methodology page sets out how every figure is computed.
Square footage questions, answered
What is square footage?
Square footage is the area of a surface measured in square feet. One square foot is a square measuring one foot on each side, so a space that is 12 feet by 15 feet contains 180 of those squares — 180 square feet. It is the standard unit for floor area in the United States, and it is what flooring, paint, tile, carpet, turf and land are all priced against.
How do you calculate the square footage of a room?
Measure the width and the length of the room in feet, then multiply them together. A room 12 ft wide and 15 ft long is 12 × 15 = 180 square feet. Measure at floor level rather than at counter height, take the width at two or three points because walls are rarely perfectly parallel, and use the smallest reading if they differ. For a room that is not a rectangle, split it into simple shapes, work out each one, and add the results.
How do I calculate square footage with feet and inches?
Enter them directly: every measurement on this site has a feet box and an inches box, and the inches box accepts fractions as well as decimals, so 6, 6.5 and 6 1/2 all work. To do it by hand, divide the inches by 12 to get a decimal fraction of a foot — 12 ft 6 in becomes 12.5 ft and 8 ft 3 in becomes 8.25 ft, so a wall 12 ft 6 in by 8 ft 3 in is 12.5 × 8.25 = 103.125 square feet.
How many square feet are in a square metre, a square yard and an acre?
One square metre is 10.7639 square feet, one square yard is exactly 9 square feet, and one acre is exactly 43,560 square feet. Roofers also use the square, which is 100 square feet of coverage. Note that a length conversion does not carry over to area: 3 feet make 1 yard, but it takes 9 square feet to make 1 square yard, because the conversion factor is squared too.
Is this square footage calculator free?
Yes. Every calculator on the site is free, needs no account and runs entirely in your browser — the measurements you type are never sent anywhere. The site is funded by display advertising, which is set out in full on the ad disclosure page.
How accurate is a square footage calculator?
The arithmetic is exact; the accuracy of the answer depends entirely on your measurements. A tape measure read to the nearest inch on a 15-foot wall carries about half a percent of error, which on a 180 square foot room is roughly one square foot. That is well inside the waste factor for any material, so it will not change what you buy. Where figures genuinely go wrong is mixing units, measuring to the wrong surface, or rounding before the final step.
Does this square footage calculator show a diagram of the room?
Yes. Below the calculator is a live scale preview that draws your space to scale as you type, on a grid whose square size is stated on the drawing, with every side labelled and the area printed inside the shape. All nine shapes are drawn rather than just rectangles, and the drawing is redrawn on every keystroke — so a measurement typed with the wrong number of digits is obvious straight away. You can also overlay a familiar object at true size, such as a queen bed, a parking space or a two-car garage, to judge how big the area really is, and download the finished diagram as a PNG or an SVG.
Can I change the measurements by dragging the drawing?
Yes. Every dimension on the live preview carries a handle you can drag, and the measurement boxes above update as you drag it. Dragging snaps to the natural step for the unit you are working in — the nearest inch in feet and inches, a quarter of a foot in feet, five centimetres in metres — and holding Shift drags freely for anything in between. The handles work from the keyboard as well: tab to one and the arrow keys move it a step at a time, or ten steps with Shift held. The awkward shapes behave properly too, so a triangle corner cannot be dragged into a triangle that could not exist, and a sector's radius and its angle move independently.
How many square feet is a 12x12 room?
144 square feet. Multiply the two sides — 12 × 12 — and that's the whole calculation, with no fractions or odd angles involved, which is probably why it's the single most-searched room size on this site. That's roughly the footprint of a small bedroom, a home office, or one bay of a garage. Enter your own numbers in the calculator above for an instant answer on a different size, or see the room size lookup page for two dozen more common dimensions already worked out.
Isn't 12x12 the same as 24 square feet?
No — that's adding the sides instead of multiplying them. Square footage always comes from multiplication: 12 feet times 12 feet is 144 square feet, not 12 plus 12. It's an easy slip to make, since doubling a number and squaring it can look similar at a glance, but a 12x12 room genuinely holds 144 of those one-foot squares. 24 would only be right if you were adding two sides together, which gets you a length, not an area.
How do I calculate the square footage of a room that isn't a rectangle?
Break it into shapes you already know how to measure, work out each one, then add them together. A circular patio uses pi times the radius squared, a triangular corner is base times height divided by two, and an L-shaped room splits into two rectangles. This site has a calculator for each of those shapes, plus trapezoids, parallelograms and sectors, so you can pick the one that matches instead of doing the geometry by hand. For a room that's a genuine mix of shapes, add each piece as its own row in the multi-room calculator and let the running total do the rest.
How many feet are 'in' a square foot?
That's a bit of a trick question — square feet and feet measure different things, so one doesn't convert into the other. A square foot is a unit of area, not length, and it takes two measurements multiplied together to make one. Ten feet of wall, on its own, has no square footage until you multiply it by a height or a width — there's no single conversion factor because a length and an area aren't the same kind of thing. Treating a length as if it were already an area is the single most common reason a square footage figure comes out wrong.
Can I estimate square footage using Google Maps?
For a rough figure on a lot or a roof, yes — Google Maps and Google Earth both have a measuring tool that lets you trace an outline and read off the area, and it's free. It's genuinely useful for land, driveways or anything you can see from above. It won't help indoors, since satellite and street imagery can't see through a roof, and even outdoors the accuracy depends on the imagery's resolution and how carefully you trace the edges — expect it to be off by a few percent rather than exact to the inch the way a tape measure is. Treat it as a starting estimate, not a final number for ordering material.