Square Footage Calculator

Square footage is length multiplied by width, and the arithmetic is the easy part. What causes problems is everything around it: rooms that are not rectangles, the waste allowance you need on top of the measured area, and materials sold in units that do not correspond to square feet. This calculator gives the area from your dimensions and, if you supply a price per square foot, the material cost — but the sections below cover the adjustments that decide whether you order enough. The short version: measure at the widest points, split irregular rooms into rectangles and add them, and buy 10% more than the calculated area for most flooring. Running out mid-job usually means a second delivery and a visible batch mismatch.

How this is calculated

Area = length × width. For a room 12 feet by 15 feet, that is 180 square feet. Material cost is that figure multiplied by the price per square foot.

For an irregular room, divide it into rectangles, calculate each separately, and add the results. An L-shaped room is two rectangles; a room with a bay window is the main rectangle plus the bay.

To convert between units, remember that one square metre is about 10.764 square feet — not 3.281, which is the linear conversion. Squaring a linear conversion factor is a frequent and expensive error when ordering from a supplier quoting in the other system.

How much extra to order

Add 10% for straightforward rectangular rooms with simple cuts. Add 15% for diagonal or herringbone layouts, which generate far more offcuts, and for rooms with many angles or obstructions.

Large-format tiles and patterned materials that need matching across joins push this higher still. Suppliers generally expect a waste allowance and will advise on their own product, but the calculated area is always a floor rather than an order quantity.

Ordering from the same batch matters as much as ordering enough. Dye lots and production runs vary slightly in shade, and a second order weeks later frequently does not match — visible in a way that a small overspend on the first order is not.

Paint is measured differently

Wall paint covers wall area, not floor area, so the floor square footage is the wrong input. Wall area is the room perimeter multiplied by the ceiling height, less the area of doors and windows.

For a 12 by 15 foot room with 8-foot ceilings, the perimeter is 54 feet, giving 432 square feet of wall before deductions. A door and two windows might remove 60 square feet. Coverage is typically quoted per gallon or litre, and two coats are the norm on anything other than a like-for-like repaint — so double the requirement before ordering.

How to use the square footage calculator

Measure length and width at the widest points. Rooms are rarely perfectly square. Measuring at the widest point means you will not come up short.
Split irregular rooms into rectangles. Calculate each rectangle separately and add the areas. An L-shape is two rectangles.
Add a waste allowance before ordering. 10% for simple layouts, 15% or more for diagonal patterns and complex rooms. Order it all in one batch.

Frequently asked questions

How do I handle an L-shaped room?

Split it into rectangles, calculate each, and add the areas together. Order 5–10% extra material for cuts and waste.

How much extra flooring should I order?

10% over the measured area for straightforward rectangular rooms, 15% or more for diagonal and herringbone layouts, which generate far more offcuts. Order it all in one batch — dye lots vary between production runs and a top-up order weeks later often does not match.

How many square feet in a square metre?

About 10.764. Note this is the linear factor of 3.281 squared — using 3.281 directly is a common and costly mistake when ordering from a supplier quoting in the other system.

Can I use this to work out how much paint I need?

Not directly, because paint covers walls rather than floors. Wall area is the room perimeter times the ceiling height, less doors and windows. Then double it, since two coats are standard on anything but a like-for-like repaint.