Renovation Materials Calculator

Features

• Four materials — paint, tiles, flooring, wallpaper — each with its own arithmetic
• Net and with-waste quantities listed separately, so the extra can be checked
• The whole number of units (tins, tiles, packs, rolls), rounded up rather than given as 2.3 tins
• Adjustable waste allowance, defaulting to the usual figure per material (tiles above flooring, wallpaper highest)
• Paint is computed as coverage × coats, with the per-coat amount listed separately
• Tiles use their size in millimetres, plus a whole-box figure at 6 per box
• The parameters are echoed back (coverage, coats, tile size) for checking against a quote
• Extreme inputs are clamped, so nothing absurd or zero comes out
• Computed locally; your room dimensions are not uploaded

How to use

1. Choose a material (paint, tiles, flooring, wallpaper)
2. Enter the area; for paint add coverage and coats, for tiles add the size
3. Adjust the waste allowance if you want (the default is the usual figure)
4. Order one step up from the result — it is an estimate, not the order quantity itself

FAQ

What waste allowance should I use?

The defaults follow common practice: flooring 5% (cutting the last row), tiles 8% (plus pattern matching and breakage; large-format or diagonal laying pushes it to 10–15%), wallpaper 10% (pattern matching, and offcuts from a roll are rarely reusable), paint 5%. The right figure depends on your layout (more corners and awkward widths mean more waste) and on how it is laid, which is why it is adjustable — and the net and waste quantities are listed separately so you can see where the extra goes.

Why does the paint coverage insist on “per coat”?

Because the labelling is ambiguous. A 10–12 m²/L figure on the tin is usually per coat, while almost all real work is two coats. Treating “per coat” as the total halves the amount, and the consequence is running out during the second coat and going back for more — and the new tin may not be the same batch, which shows as a slight colour difference. So the number of coats is its own parameter here, defaulting to 2, with the per-coat amount also listed.

Why give a box count for tiles as well?

Because tiles are usually sold by the box, and how many are in a box depends on the size (commonly 4–10). The figure here assumes 6 per box, purely to give a feel for how many boxes you will be carrying — order using the per-box count the shop states, which varies. The tile count is the main result; the box count just makes the quantity tangible (9 boxes reads differently from 51 tiles).

Can I order exactly what it says?

Order one step up rather than to the number. These are estimates: wall flatness, substrate absorption, the laying pattern (diagonal uses more) and wallpaper pattern repeat all change the real consumption. And a mid-job top-up has real costs — dye-lot differences in tiles and wallpaper, colour-batch differences in paint. Buying a little extra costs far less than one more trip, especially halfway through a job.