Finishes quantity calculator
Net wall area is 2 x (length + width) x height minus the doors and windows. Paint litres are the area times coats divided by coverage. Sheets of board and floor tiles are the area plus waste divided by the area of one piece, rounded up. All sizes are in metres or millimetres.
On this page
Areas
Enter the room's length, width and height in metres, then the number and size of doors and windows. Gross wall area = 2 x (length + width) x height. Openings = doors x width x height + windows x width x height. Net wall area = gross wall area minus openings. Ceiling area and floor area are both length x width.
If the openings add up to more than the walls, the net wall area is shown as 0 and the tool warns you, because a negative area makes no sense. Check the sizes in that case. The calculator treats one rectangular room, so for several rooms run it for each one and add the results.
Paint, board and tiles
Paint litres = area x coats / coverage in m2 per litre. You choose whether to paint the walls, the ceiling or both. The coverage of 10 m2 per litre is an example. Spread rates are often quoted around 10 to 12 m2 per litre, but the figure on the tin for your product and surface is the one to use. The tool shows the exact litres and the litres rounded up to a whole number.
Gypsum board sheets = ceil(area x (1 + waste %) / sheet area). The default sheet is 2.4 m x 1.2 m, which is 2.88 m2, and you can change both sides and the waste. Floor tiles = ceil(floor area x (1 + waste %) / tile area), where the tile area comes from the width and length in millimetres divided by 1,000,000. Typical waste allowances depend on the layout, with diagonal patterns and large tiles needing more.
Using the quantities on site
Quantities for finishes become orders and then claims. Material arriving on site is checked and recorded in site stores, and finished work is evidenced through quality and handover with a work inspection report and a material inspection report. Read the document control guide and the procurement guide.
For the money side see the payment certificate calculator, the retention calculator, the VAT calculator and the rebar weight calculator. A submittal is normally needed for finishes materials before they are ordered.
Worked example
A room 5 m x 4 m x 3 m high with one door of 0.9 x 2.1 m and two windows of 1.2 x 1.2 m. Two coats on walls and ceiling, board on both, 10% waste, 600 x 600 mm tiles.
| Quantity | Working | Result |
|---|---|---|
| Gross wall area | 2 x (5 + 4) x 3 | 54.00 m2 |
| Openings | 0.9 x 2.1 + 2 x 1.2 x 1.2 | 4.77 m2 |
| Net wall area | 54 - 4.77 | 49.23 m2 |
| Ceiling and floor | 5 x 4 | 20.00 m2 each |
| Paint | (49.23 + 20) x 2 / 10 | 13.85 L (14 L) |
| Gypsum board | ceil(69.23 x 1.1 / 2.88) = ceil(26.44) | 27 sheets |
| Floor tiles | ceil(20 x 1.1 / 0.36) = ceil(61.11) | 62 tiles |
Worked example
A room 5 m x 4 m x 3 m has gross walls of 2 x 9 x 3 = 54 m2. One door of 0.9 x 2.1 and two windows of 1.2 x 1.2 take out 4.77 m2, leaving 49.23 m2. With the 20 m2 ceiling, two coats at 10 m2 per litre need 69.23 x 2 / 10 = 13.85 litres, or 14 whole litres. Board on walls and ceiling with 10% waste needs ceil(69.23 x 1.1 / 2.88) = 27 sheets, and the floor in 600 x 600 mm tiles needs ceil(20 x 1.1 / 0.36) = 62 tiles.
Questions people ask
How do I calculate wall area for paint?
Multiply the perimeter by the height, then subtract the doors and windows.
What paint coverage should I use?
The figure on the tin for your product and surface. The 10 m2 per litre in the box is only an example.
How many coats does the tool assume?
Two, as a starting value. You can enter any number, including 0.
Does it subtract the doors and windows?
Yes, by the sizes and numbers you enter. If they exceed the wall area, the net area is shown as 0.
What size is a gypsum board sheet?
The default is 2.4 m x 1.2 m, which is 2.88 m2. Change it to match the board you buy.
How much waste should I allow?
It depends on the layout. The 10% is an example. Cut-heavy layouts and large tiles need more.
Why are sheets and tiles rounded up?
You cannot buy part of a sheet or tile, and rounding down leaves the area uncovered.
Can I do more than one room?
Run each room separately and add the results, because the tool handles one rectangular room.
Does it include skirting or cornices?
No. It covers walls, ceiling and floor only.
Does it use imperial units?
No. Lengths are in metres, tile sizes in millimetres and paint in litres.