How much do you actually need to buy?

Why another calculator site

Because almost every other one stops one step short. You measure the room, you get a number in square feet, and then you are standing in an aisle doing division on your phone to work out how many boxes that is.

These carry on to the end. Every calculator here answers in things you can actually put in the cart — bags, sheets, boxes, boards, bundles, gallons — because that is the number that decides whether you make one trip or three.

Three things we do differently

• Rooms that are not rectangles. L-shaped, with an alcove, a chimney breast or a bay window? Add a section for each part and we total them. Nearly every other calculator gives you one length box and one width box and leaves the rest to you on paper.
• The whole order, not just the headline. The drywall calculator gives you screws, tape and compound. The tile one gives you thinset and grout. The paver one gives you base gravel, bedding sand, jointing sand and edge restraint. Those are the items people forget and drive back for.
• The arithmetic is shown. Every page lists each step it ran and where each figure came from. If you disagree with a step, you can see exactly which one — and tell us, through a link at the bottom of every page.

Every calculation runs inside your own browser — your measurements are not sent to us unless you ask us to email you the list. That also means the numbers keep working on a bad signal at the back of a lumber yard, which is, in our experience, exactly where they are needed.

How we check the numbers · Guides · All calculators