Square footage is the number behind almost every home-improvement estimate. Paint, flooring, tile, drywall, insulation — they all start from the area you are covering. Get this one figure right and every downstream calculation is sound; get it wrong and the error follows you to the checkout. This calculator does the basic length-times-width maths and converts between square feet and square metres, and the guide below shows how to handle the awkward shapes that real rooms throw at you.
The basic formula
For walls: area = width × height
Total = area × number of identical areas
That is all there is to a rectangle. The skill in measuring area is not the multiplication — it is breaking a real, irregular space into rectangles you can multiply.
Measuring rectangular spaces
- Measure in one consistent unit — all feet or all metres — and convert at the end if needed.
- Measure the longest points in each direction; walls are rarely perfectly square.
- Use the count field when you have several identical rooms or walls, rather than adding them up by hand.
Formulas for non-rectangular shapes
| Shape | Area formula |
|---|---|
| Rectangle / square | length × width |
| Triangle | ½ × base × height |
| Circle | π × radius² |
| Trapezoid | ½ × (a + b) × height |
For a curved or rounded room, approximating it as the nearest rectangle or circle is usually close enough for material ordering, where a waste factor covers small errors.
A worked example
An L-shaped living-dining room made of a 14×12 ft section and a 10×8 ft section:
- Section one = 14 × 12 = 168 sq ft
- Section two = 10 × 8 = 80 sq ft
- Total = 168 + 80 = 248 square feet
Converting between units
Square feet and square metres trip up a lot of projects, especially when a product is sold in one system and you measured in the other. One square metre is about 10.76 square feet, so to go from feet to metres divide by 10.76, and to go the other way multiply. The calculator shows both figures at once so you never have to do it by hand.
Where this number goes next
Once you have an accurate area, the rest of the project opens up: feed it into the flooring calculator for boxes, the paint calculator for gallons, the tile calculator for tile count, or the drywall calculator for sheets. This single figure is the doorway to every material estimate on the site, which is why it is worth measuring carefully and writing down.
Tackling truly awkward rooms
Most rooms that look impossible to measure are just a few simple shapes in disguise. An L-shaped room is two rectangles; a room with a bay window is a rectangle plus a trapezoid or a half-hexagon; a room with an angled wall is a rectangle plus a triangle. The technique is always the same: divide the floor into shapes you have a formula for, measure each, calculate its area, and add them up. Sketch the room on paper, draw the dividing lines, and label each piece with its dimensions — the arithmetic becomes trivial once the shapes are separated, and you are far less likely to miss or double-count an area.
Circles, triangles and curves
Beyond rectangles, two formulas cover almost everything. A triangle's area is half its base times its height — useful for angled corners and gable walls. A circle's area is pi times the radius squared, for round patios and columns; a half-round bay is simply half of that. For a genuinely curved edge, approximate it as the nearest rectangle or as a series of straight segments; the small error is well within the waste factor that material orders include. You rarely need precise calculus for home projects — sensible approximation of curves into known shapes is accurate enough for buying materials.
The feet-and-inches trap
A frequent and costly error is mixing units mid-measurement. Twelve feet six inches is not 12.6 feet — it is 12.5 feet, because six inches is half a foot, not six-tenths. Convert inches to a decimal fraction of a foot (divide by twelve) before multiplying, or measure everything in inches and convert the final area. Being sloppy here can throw an estimate off by enough to matter on an expensive material. The same care applies when a product is sold in metric and you measured in imperial: convert deliberately rather than eyeballing, and let the calculator show both figures so you can cross-check.
Turning area into a materials order
Square footage is rarely the end goal — it is the input for a material estimate, and each material adds its own twist. Flooring and tile add a waste factor and round to whole boxes; paint converts area to gallons via a coverage rate; drywall and plywood divide by sheet size. That is why this site has a dedicated calculator for each: they take the accurate area you establish here and apply the right rules for that product. Measure once, carefully, write the number down, and feed it into the relevant tool rather than re-measuring for every material — the area does not change, only what you do with it.
A number you will reuse constantly
Square footage is the most-used measurement in home improvement, and establishing it accurately once saves repeated effort. Real estate, flooring, paint, tile, insulation, heating and cooling sizing, and even property tax assessments all rest on area. Measure each room carefully, record the figures with a sketch, and you have a reference for every future project in that space rather than re-measuring each time. For whole-house figures, sum the rooms and circulation; for projects, use the relevant room or wall. Keep in mind that finished, heated floor area is measured differently from gross area including garages and unfinished spaces, which matters for listings and assessments. Whatever the purpose, the discipline is the same: break the space into simple shapes, measure in consistent units, multiply and add. The calculator handles the arithmetic and the metric conversion; your careful measuring and sketching are what make the result trustworthy enough to build and budget on.
Frequently asked questions
How do I calculate square footage?
Multiply length by width. A room 12 ft long and 10 ft wide is 12 × 10 = 120 square feet. For walls, multiply width by height.
How do I find the square footage of an irregular room?
Divide the room into rectangles, calculate the area of each, and add them together. For triangular sections, use ½ × base × height; for circles, π × radius squared.
How do I convert square feet to square metres?
Multiply square feet by 0.0929, or divide by 10.764. So 120 sq ft is about 11.15 m². The calculator shows both automatically.
Why does square footage matter for projects?
It is the starting point for nearly every material estimate — paint, flooring, tile, drywall and more all begin with an accurate area. Get this number right and the rest follows.