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Square Footage Calculator

Work out the square footage of a room, a floor plan or any shape — rectangle, triangle, circle, trapezoid, parallelogram or ellipse — in any of seven units. Enter your dimensions and the answer updates as you type.

6 shapes7 length unitsCalculated in your browser

Calculate square feet for any shape

Pick a shape, choose a unit, and fill in the dimensions. The formula in use is shown with your own numbers substituted into it.

Shape

Formula: A = length × width

A = 10 × 5

50 m2

The same area in other units

UnitArea
m250
cm2500,000
km20.00005
in277,500.155
ft2538.1955
yd259.7995
mi20.00001931

Conversion factors are the squares of the exact unit definitions — one inch is exactly 2.54 cm, one foot is 12 inches, one yard is 3 feet and one mile is 5,280 feet.

Area formulas at a glance

ShapeFormulaWhat to measure
RectangleA = length × widthLength · Width
TriangleA = ½ × base × heightBase · Height
CircleA = π × radius²Radius
TrapezoidA = ½ × (base a + base b) × heightBase a · Base b · Height
ParallelogramA = base × heightBase · Height
EllipseA = π × semi-axis a × semi-axis bSemi-axis a · Semi-axis b

Using the square footage calculator

Three steps, and no sign-in.

  1. Pick the shape

    Choose rectangle, triangle, circle, trapezoid, parallelogram or ellipse. The input fields change to match the measurements that shape actually needs.

  2. Enter the dimensions

    Set the unit once — every dimension for a shape is read in that same unit. Convert first if your measurements are currently a mix of metres and feet.

  3. Read the result

    The area appears in your chosen unit squared, followed by a table giving the identical area expressed in each of the other six units.

What this calculator does

A small tool, but an honest one — here is exactly what is going on behind the input boxes.

  • Six shapes

    Rectangle, triangle, circle, trapezoid, parallelogram and ellipse — between them these cover most rooms, plots, worktops and openings you will need to size.

  • The formula is on screen

    Every result shows both the general formula and the same formula with your numbers filled in, so you can check the working instead of trusting a black box.

  • Seven length units

    Metres, centimetres, kilometres, inches, feet, yards and miles. The result is labelled in the squared form of whichever unit you picked.

  • Exact conversion factors

    Area conversions are the squares of the exact unit definitions — an inch is exactly 2.54 cm, a foot exactly 12 inches — rather than rounded decimals copied off a chart.

  • Nothing is uploaded

    The arithmetic runs in JavaScript on the page in front of you. No dimension you type is sent to a server.

  • Guarded inputs

    Blank, negative and zero dimensions produce a plain hint rather than a meaningless number. You will never see NaN in the result box.

How to find the square footage of an irregular room

Very few real rooms are a single clean shape. The reliable method is to break the floor into pieces that each match one of the shapes above, calculate them one at a time, and add the results together. An L-shaped living room is two rectangles; a room with a bay window is a rectangle plus a trapezoid or a half-ellipse.

Alcoves, chimney breasts and boxed-in pipework work the same way in reverse: calculate the full rectangle, calculate the intrusion, and subtract. Doing it piece by piece is also easier to check later than one clever formula you will not remember the reasoning behind.

Measure at floor level rather than at waist height, and take each wall in two places if the building is old — walls that look parallel often are not, and a trapezoid is frequently a better fit than a rectangle.

Pick your unit before you start measuring

All the dimensions in a single calculation share one unit, which is deliberate: mixing units inside a shape is the most common way area calculations go wrong. If your tape measure reads feet and inches, convert everything to decimal feet or everything to inches before entering it.

Converting once at the end is safer than converting each measurement as you go, because rounding a value at every step compounds the error. The conversion table below each result lets you take a single accurate figure into whichever unit the next person needs.

Where an area figure gets used

Floor area drives most material estimates: flooring and underlay, tile counts, screed volume, insulation, and the coverage figures printed on paint tins. Suppliers normally quote coverage per square metre or per square foot, so getting the area right is the step everything else hangs off.

It also matters for compliance and comparison — minimum room sizes, rental listings and heating calculations are all expressed as areas. When you are ordering materials, add a waste allowance on top of the calculated area rather than inflating the measurement itself, so you keep the true dimension recorded somewhere.

Square Footage Calculator FAQ

Measure the length and width in feet and multiply them: a room 12 ft by 15 ft is 180 sq ft. If the room is not a rectangle, split the floor into simple shapes, work out each one, and add the results. Measure wall to wall at floor level, not across skirting or furniture.

Multiply the length by the width, with both figures in the same unit. A room measuring 10 m by 5 m has an area of 50 m². If one measurement is in metres and the other in centimetres, convert first — otherwise the answer is off by a factor of 100.

Half the base multiplied by the perpendicular height: A = ½ × b × h. The height is the straight-line distance from the base to the opposite corner measured at a right angle to that base, which is not the same as the length of a slanted side.

Multiply by 10.7639, which is 1 divided by 0.3048 squared, because a foot is defined as exactly 0.3048 metres. Note that the area factor is the square of the length factor, so it is roughly 10.76 rather than 3.28. The table under each result does this conversion for you.

Multiply the length by the width in inches, then divide by 144, because a square foot is 12 × 12 = 144 square inches. A floor 90 in by 120 in is 10,800 sq in, or 75 sq ft. Alternatively, choose inches as the unit here and read the square feet figure from the conversion table.

Yes, by splitting it. Divide the L into two rectangles, calculate each one, and add them together. The same approach handles any irregular outline: break it into shapes the calculator supports, then add the pieces, subtracting any alcoves or recesses.

A waste allowance of around 5–10% is common for straight-laid flooring, and more for diagonal or patterned layouts, where offcuts are harder to reuse. Add it to the calculated figure rather than to your measurements, and check the manufacturer’s own guidance, which varies by product.

The radius, which is half the diameter. If you measured across the full width of a circular feature, divide that figure by two before entering it — using the diameter by mistake makes the area four times too large.

No. The calculator is plain JavaScript running in the page, so your dimensions stay in the browser tab. There are no network calls involved in producing a result, and nothing is stored between visits.

Turn those measurements into a floor plan

Once you know the dimensions, describe the rooms in a short brief and generate a labelled floor plan image to see how the space could work.

Start a floor planConvert cm to feet