Square Footage Calculator

How this is calculated

sq ft = (length ft + in⁄12) × (width ft + in⁄12)    m² = sq ft ÷ 10.7639

Worked example (the defaults): 12 ft 6 in × 10 ft = 12.5 × 10 = 125 sq ft (11.61 m²). With the +10% plank-flooring allowance, buy for 137.5 sq ft — in 20 sq ft boxes, that's 7 boxes, with sensible spares left for the radiator pipe cut you haven't discovered yet.

Multiple rooms

Run each room through and add the results (a note app or the copy button keeps the running list). Add the waste allowance once at the end on the total, not per room — waste pools across the whole job, which is why pros calculate it last.

Measuring a room that is not a rectangle

Most real rooms are rectangles with pieces added or removed, and the reliable method is to break the shape into rectangles, calculate each, and add or subtract. An L-shaped room splits into two rectangles along an imaginary line; measure both, add them. A chimney breast or a built-in cupboard is a rectangle to subtract. A bay window is a rectangle plus a triangle, and a triangle is base × height ÷ 2.

Sketch the room, write the measurements on the sketch, and do the arithmetic afterwards. Trying to hold six numbers in your head while balancing on a chair is how the wrong quantity gets ordered.

What to add for waste — and why

Never order exactly the calculated area. The standard allowance is 5–10% for straightforward layouts and 10–15% for diagonal or herringbone patterns, complicated shapes, or large-format tiles where every cut wastes a big piece. Patterned wallpaper and patterned flooring need more still, because matching the repeat throws away material at every drop.

There is a second reason beyond offcuts. Tiles and flooring are manufactured in batches, and batches vary slightly in shade. Ordering short and topping up later frequently means a visible mismatch, so the spare material is also insurance for future repairs — keep the leftovers with the batch number.

Common conversions

From	To	Multiply by
Square feet	Square metres	0.092903
Square metres	Square feet	10.7639
Square yards	Square feet	9
Acres	Square feet	43,560
Hectares	Square metres	10,000

Note that area factors are the square of length factors — a foot is 0.3048 m, and 0.3048² = 0.092903. This is why doubling a room's dimensions quadruples its area, and why "twice the size" is ambiguous enough to be worth clarifying before anyone orders anything.

Buying paint, flooring and turf from an area

Paint is sold by coverage per litre, typically 10–14 m² for emulsion on a smooth sealed wall, and much less on bare plaster or a strong colour change. Remember to calculate wall area rather than floor area: perimeter × height, less doors and windows. Two coats double the requirement, and most colours need two.

Flooring is sold by the pack with a stated coverage, so divide your area-plus-waste by the pack coverage and round up — you cannot buy two-thirds of a pack. Turf is sold by the roll or the square metre and should be ordered to arrive on the day you lay it, since it deteriorates quickly on the pallet.