Frequently asked questions

Calculate the floor area, then allow for the fixed roll width — usually 12 ft — which forces a seam and waste in any room wider than the roll.

Both — one square yard is 9 square feet, so always check which unit a quote uses before comparing prices.

Allow 10% on a simple room and more when the room is wider than the roll; stairs are quoted per tread rather than by area.

Underlay covers the same floor area but comes in different roll sizes and needs only about 5% waste, since there is no pattern to match.

Halve the diameter to get the radius, then multiply pi by the radius squared: a 16 ft circle is about 201 square feet.

Measure across the circle and take the longest reading; check it again at right angles, and if the two differ the shape is an oval, not a circle.

Calculate the area, then add 15–20% waste rather than the usual 10% — every edge piece around a circle has to be cut on a curve.

Divide the total wall and ceiling area by the sheet coverage — 32 sq ft for a 4 by 8 sheet, 48 for a 4 by 12 — and round up.

No — the cut-outs are rarely reusable, so count the wall as solid and treat openings as waste unless they are unusually large.

Roughly one gallon of joint compound and 40 linear feet of tape per 100 square feet of drywall for a standard three-coat finish.

Longer 4 by 12 sheets reduce hard-to-finish butt joints on long walls, but 4 by 8 is easier to handle and fine for most rooms.

Add up the floor areas, add 10% waste, divide by the coverage per box and round up to whole boxes.

Add 10% for a simple room, 15% for a complex or diagonal lay, and 20% for wide planks or strong patterns — and keep a spare box.

Floor through closets and under free-standing appliances, but subtract fixed base cabinet runs you will not floor under.

Measure each room to the centre of its doorway so the threshold is counted once, and add roughly 3 sq ft per door for the strip itself.

Square footage is area measured in square feet — the number of one-foot squares that fit inside a space, calculated for a rectangle as length multiplied by width.

Multiply the room's width in feet by its length in feet: a 12 ft by 15 ft room is 180 square feet.

Enter the feet and the inches in their own boxes, or by hand divide the inches by 12: 12 ft 6 in is 12.5 ft, so 12 ft 6 in by 8 ft 3 in is 103.125 square feet.

A square metre is 10.7639 square feet, a square yard is 9 square feet, an acre is 43,560 square feet, and a roofing square is 100 square feet.

Yes — every calculator is free, requires no account, and runs in the browser without sending your measurements anywhere.

The calculation itself is exact, so accuracy comes down to your measurements — reading a tape to the nearest inch keeps a typical room within about one square foot.

Yes — a live scale preview below the calculator draws the space to scale on a measured grid, labels every side, prints the area inside the shape, and downloads as a PNG or SVG.

Yes — each dimension on the live preview has a drag handle that writes straight back to the measurement boxes, snapping to the natural step for the unit, and the arrow keys do the same from the keyboard.

A 12 by 12 foot room is 144 square feet — multiply the two sides together (12 × 12) to get the floor area.

No — 12x12 means 12 feet multiplied by 12 feet, which is 144 square feet, not 12 plus 12.

Split the room into simple shapes — rectangles, circles, triangles — work out each one's area, and add them together; each shape has its own calculator on this site.

Square feet measure area and feet measure length, so one doesn't convert into the other — you need two measurements multiplied together to get square feet.

Yes, for outdoor spaces like a lot or a roof — Google Maps and Google Earth both have a measuring tool — but it can't see indoors and is only accurate to within a few percent.

Gross living area is the finished, heated, above-grade floor area measured to the exterior walls, excluding garages, unfinished space and basements.

No — a finished basement is reported as separate below-grade finished area, not included in gross living area, under ANSI Z765.

Stairs count on each floor they serve, but the opening they pass through is subtracted from the floor above, as are two-storey voids.

At least 7 feet over most of the floor; under a sloped ceiling, half the area must reach 7 feet and only floor with 5 feet of headroom counts.

No — it applies the ANSI Z765 arithmetic to areas you classify, but it cannot judge whether a space qualifies, which is an appraiser's job.

Calculate the floor area, add waste, then divide by the box coverage — typically 18 to 24 square feet — and round up.

Allow 10% for narrow boards, 15% for wide planks and up to 20% for a diagonal lay, and keep a spare box for future repairs.

No — the area is the same, but running boards along the longest wall wastes less than running them across or diagonally.

Yes — most manufacturers require three to five days acclimating in the room, opened, before installation, or the boards may cup or gap.

Measure the full outer rectangle, subtract the missing corner rectangle: 20 by 16 ft with a 6 by 8 ft notch is 272 square feet.

Yes — splitting into two non-overlapping rectangles and adding them gives exactly the same area as subtracting the notch.

Subtract each missing rectangle in turn, or sketch the outline on the drawing canvas and let it compute the whole polygon at once.

Around 7 standard bricks per square foot of wall, though it shifts with the brick size and the mortar joint you're using. That figure is based on the common modular brick, laid with a standard 3/8 inch mortar joint; a larger brick or a thicker joint needs fewer per square foot, a smaller brick or thinner joint needs more. Add 5 to 10% on top for cuts, breakage and corners, and check the coverage rate printed on the specific brick you're buying rather than relying on a general rule — sizes vary more between products than people expect.

It depends entirely on how thick the slab is, because concrete is ordered by volume, not area. Multiply the square footage by the slab thickness in feet, then divide by 27 to get cubic yards — a 4-inch slab is 0.333 ft thick, so 100 square feet at 4 inches is 100 × 0.333 ÷ 27, about 1.23 cubic yards. A thicker driveway slab at 6 inches needs roughly 1.85 cubic yards for that same 100 square feet. Round up to the nearest quarter yard and add a little extra — most ready-mix suppliers have a minimum order anyway, and running short mid-pour isn't an option.

Divide the total rent for the period by the square footage of the space. If a 2,000 square foot office costs $4,000 a month, that's $4,000 ÷ 2,000 = $2 per square foot per month, or $24 per square foot annually. Commercial leases usually quote the annual figure, so it's worth converting before comparing two listings — a space advertised at $2 a month and another at $22 a year are close but not identical ($24 vs $22). Also check which square footage is being used: some landlords quote rentable square feet, which includes a share of hallways and lobbies, rather than the usable square feet you actually occupy.

Measure each room separately — including hallways, stairs and closets — and add the areas together rather than measuring the whole floor at once.

Yes for materials, and for a property figure hallways and closets count while a stairwell opening is subtracted from the floor above.

Yes — each row takes its own shape, so circles, triangles and rectangles all add into one running total.

Listings quote gross living area measured to the exterior walls, which typically runs 3–6% above a room-by-room interior total.

Add each wall's width times the ceiling height, subtract doors and windows, then divide by the tin's coverage and multiply by the number of coats.

About 350–400 square feet per coat on primed smooth drywall, dropping to 200–250 on bare or textured surfaces.

Deduct about 21 sq ft per door and 15 per window, though under 100 sq ft of openings most decorators skip it — cutting-in absorbs the difference.

Assume two coats for any colour change; one coat only works for a refresh in the same colour, and dark-to-light usually needs a primer plus two.

Multiply the base by the perpendicular height: a 16 ft base with a 9 ft height is 144 square feet.

The sloping side overstates the area — only the perpendicular distance between the parallel sides matters, and at 45 degrees the error is about 41%.

Diagonal parking bays, slanted driveways, angled decks and diagonal tile layouts are the parallelograms that come up most often.

32 square feet. A standard sheet good — plywood, OSB, drywall — is sold at 4 feet by 8 feet, so 4 × 8 gives you 32 square feet of coverage per sheet, before any cuts or waste. That's the number to divide your total area by when working out how many sheets to buy: a 300 square foot wall needs at least 10 sheets (300 ÷ 32 = 9.4, rounded up), plus a bit extra for cuts around doors, windows and corners.

144. A foot is 12 inches, so a square foot — one foot by one foot — is 12 inches by 12 inches, and 12 × 12 = 144 square inches. That's also the answer to whether 12x12 inches makes a square foot: it does, exactly. Going the other way, divide a figure in square inches by 144 to get square feet — 300 square inches is 300 ÷ 144, or about 2.08 square feet.

There's no fixed answer — square feet measure a flat area and cubic feet measure a volume, so you need a third dimension, height or depth, to go from one to the other. Multiply the square footage by that height in feet to get cubic feet: 100 square feet of floor with a 1-foot-deep layer of gravel on top is 100 cubic feet, but the same 100 square feet at 6 inches deep is only 50 cubic feet, because 0.5 ft is the height you're using. This is exactly the calculation behind ordering mulch, topsoil, gravel or concrete — get the depth right and the volume follows.

No, and mixing them up is a common source of confusion, especially outside the US. Square footage here is a plain measurement — length times width, whatever surface you're measuring. Carpet area is a specific real estate term, used mainly in India and defined under RERA, for the usable floor space inside a unit's walls, excluding the walls themselves, balconies, and any shared common areas. It sits below built-up area (carpet area plus the walls) and super built-up area (built-up area plus a share of lobbies, stairwells and other shared spaces), which is why a flat advertised at 1,000 square feet of super built-up area might only have 700 to 750 square feet of actual carpet area inside it. If you're comparing listings, check which of the three figures is being quoted before comparing price per square foot.

A single bedroom typically runs 10x10 to 12x12 feet — 100 to 144 square feet — while a primary bedroom is usually bigger, 12x15 to 14x16, or roughly 180 to 225 square feet. A living room tends to run 12x18 to 16x20, so 216 to 320 square feet. A 2BHK flat (two bedrooms, a hall and a kitchen) varies a lot by market, but commonly falls somewhere between 600 and 900 square feet of carpet area, or roughly 850 to 1,100 square feet of built-up area once the walls and common spaces are added in. These are typical ranges rather than a fixed rule, so don't be surprised by a smaller room in an older building or a larger one in new construction — measure the actual space with the calculator above rather than assuming the average applies.

Multiply width by length in feet: a 12 ft by 15 ft rectangular room is 180 square feet.

No — width times length gives the same area either way round, so 12 by 15 and 15 by 12 are both 180 square feet.

Subtract permanently fixed floor obstructions such as islands when buying flooring, but include closets — and for a property listing, count closets as living area.

Multiply pi by the radius squared, then by the angle divided by 360: a 90-degree sector with a 10 ft radius is 78.54 square feet.

Most sectors on site are obvious quarter-circles (90 degrees) or half-circles (180 degrees); otherwise measure the radius and the chord across the ends of the curve.

Rounded patio corners, fan-shaped decks, curved driveway aprons and half-round pool ends are the sector shapes that come up most.

Multiply the side length by itself: a square room 14 ft on each side is 196 square feet.

Loosely they mean the same, but strictly 4 square feet is an area of 4 sq ft while 4 feet squared is a 4 ft by 4 ft square, which is 16 sq ft.

Take the square root of the area: a 400 square foot square room is 20 ft on each side.

Calculate the area, add 10–15% waste, divide by the coverage per box and round up: a 180 sq ft floor at 10% waste needs 198 sq ft of tile.

Add 10% for a straight lay, 15% for diagonal or herringbone, and buy the extra in the same order so the dye lot matches.

Subtract permanently fixed floor obstructions such as base cabinets and islands, but tile under toilets and free-standing appliances.

Multiply width by height for each wall and subtract openings; a 12 ft run with an 18 in backsplash is 18 square feet before waste.

Average the two parallel sides and multiply by the height between them: parallel sides of 14 ft and 10 ft, 8 ft apart, give 96 square feet.

The parallel sides are the pair that stay the same distance apart along their whole length; if no pair does, split the shape into two triangles.

Bay windows, widening driveways, gable ends and angled extensions are the trapezoids that come up most in a house.

Multiply the base by the perpendicular height and divide by two: a 12 ft base with a 9 ft height is 54 square feet.

The height is the perpendicular distance from the base to the opposite corner, not the length of the sloping side.

Use the three-sides version whenever a perpendicular height is hard to measure — three side lengths are easier to take and give the same area.

Heron's formula: halve the perimeter to get s, then take the square root of s(s−a)(s−b)(s−c) — sides of 9, 12 and 15 ft give 54 square feet.

Any two sides must add up to more than the third; if they do not, the measurements cannot form a triangle and one of them is misread.

Mark the three corners and measure each side corner to corner with the tape flat and taut, taking horizontal distances rather than following any slope.