Renovation calculators

How much to buy so you neither run short nor end up with half a pallet left over. Each calculator runs in your browser, shows the formula and tells you how much allowance to add — because the allowance is usually what decides whether you have enough.

• Paint calculator Litres and tins for a room, using the coverage on the label and the number of coats.
• Tile calculator Tiles and boxes for a floor or a wall, with the cutting allowance.
• Flooring calculator Packs of laminate and how many square metres you actually buy.
• Wallpaper calculator Rolls — calculated in drops and with the pattern repeat.

Why quantities are harder than they look

Each of these materials is calculated differently, and that is the problem. Paint comes from wall area times the number of coats. Tiles and flooring come from area plus a cutting allowance, but they are sold in boxes, so you round up twice. Wallpaper is not calculated from square metres at all — it goes by drops, because the remainder of a roll shorter than the wall is waste.

That is why a generic "area times something" calculator is always wrong. These four follow the rules that actually apply to each material.

Where to get the dimensions

Every calculator needs the dimensions of the room. You can measure them with a tape — or scan the room with your phone in the Decoria.Studio app, which works out the wall and floor area itself and then builds a complete shopping list with quantities, prices and a fit to your budget.