How to use the material calculator
- Enter the room length, width and ceiling height, and the number and size of doors and windows.
- For paint, choose the coats and coverage per liter; for tiles, the tile size and joint gap; for wallpaper, the roll size.
- The cards below show liters of paint and cans, number of tiles and boxes, and wallpaper rolls. Changing a value recalculates at once.
The basics of area calculation
The first step to estimating materials in a DIY renovation is area. Wall area is the room perimeter (length plus width, doubled) times the ceiling height, and subtracting doors and windows gives the area to be painted. Floor and ceiling are length times width. This calculator finds the areas in this order and then applies the rules for each material.
For paint, the paint area is multiplied by the number of coats, divided by the coverage per liter, and a waste allowance is added. For tiles, the surface area is divided by the area of one tile including its joint gap. For wallpaper, the wall perimeter is divided by the roll width to get the number of strips, and that is divided by the strips one roll yields to get the number of rolls.
Why waste allowance and specifications matter
Buying exactly the calculated amount of material tends to fall short. Paint is absorbed by the wall and stays on the roller, tiles are lost to cutting and breakage, and wallpaper needs pattern matching and trim at top and bottom. A 5 to 10% allowance is common. The same product from another production batch can differ slightly in color, so buying enough at the start is safer than buying more later.
Specifications differ by product. Enter the coverage from the paint label, and change the wallpaper width and length and the tile size and pieces per box to match what you buy. The defaults here assume commonly used sizes and are only a reference. Curved or sloped ceilings, moldings and baseboards need to be calculated separately.
Check before you buy
- Measure the room yourself with a tape measure.
- Check the coverage on the paint label.
- Buy tiles and wallpaper from the same production lot at once.
- Keep leftover material for repairs.
- For big jobs, compare with a contractor's estimate.
FAQ
How many coats of paint are needed?
Two coats after a primer is the usual assumption, but putting a light color over a dark one or painting a very absorbent wall can need more. You can change the number of coats here, and entering the coverage (sq m per liter) from the product label makes it more accurate.
Why leave extra tiles?
Cut-offs, breakage and spare pieces for later repairs all need extra tiles. About 10% is typical, and diagonal layouts or complex patterns need more. The same product from a different production batch can differ slightly in color, so buying everything at once is better.
How is the number of wallpaper rolls calculated?
The wall perimeter is divided by the roll width to get the number of strips, and then the number of strips one roll gives at the wall height (with trim) is worked out. Patterned wallpaper needs extra length to match the pattern. This calculator does not subtract doors and windows, so it is a generous estimate.
Notes & limitations
This calculator gives reference estimates for a rectangular room. Actual needs vary with room shape, method and product, so check the product label and the seller's guidance before buying.