Wall Area Calculator
Calculate wall surface area
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Need a fast answer on calculating wall surface area? Wall Area Calculator answers with the steps beside it. You supply Length (m), Height (m) and Doors Area (m²) to Wall Area; the answer follows at once. In Wall Area the working sits beside the answer. Wall Area suits budgeting and planning checks. You can disconnect once Wall Area has loaded; the arithmetic runs locally. Wall Area is part of the Construction collection on CalcProMaster, alongside wall area calculator, free online wall area calculator and more. Wall Area is great for comparing scenarios. Change one value and watch. Wall Area answers the next Construction question you meet.
What the defaults give
A wall 10 m long and 3 m high is 30.00 m² of surface; after 2 m² of doors and 3 m² of windows, 25.00 m² is left to cover.
The openings are entered as areas in square metres, not as a count of doors and windows.
How to calculate wall area
Net wall area = length × height − doors − windows
A 10 m wall at 3 m high is 30 m² gross; minus a 2 m² door and 3 m² of window, the net area is 25 m².
| Gross area | Openings | Net area |
|---|---|---|
| 30 m² | 5 m² | 25 m² |
| 40 m² | 6 m² | 34 m² |
| 50 m² | 8 m² | 42 m² |
Deduct the openings once, not per coat: paint is estimated from the net area, then multiplied by the number of coats. At 10 m² per litre per coat, 25 m² needs 2.5 L for one coat and 5 L for two. Measure each wall separately if the lengths differ, and add gable triangles as half of base × height.
Related: paint quantity and drywall sheets.
The formula
Net area = length × height − door area − window area
The first multiplication is the gross rectangle. The subtraction is what stops you buying paint for surface that will not be painted. The tool reports both numbers so you can see how much of the wall the openings take: here 5 m² of 30 m², one sixth of the surface.
Worked examples
10 × 3 m with 5 m² of openings → 25.00 m²
5 × 3 m → 10.00 m² net
20 × 3 m → 55.00 m² net
10 × 1.5 m → 10.00 m² net
10 × 6 m → 55.00 m² net
Four doors instead of two → 23.00 m² net
Six square metres of window instead of three → 22.00 m² net
Length and height move the answer in step: double the length and the net area doubles, because the openings stay the same. That is the useful behaviour when you are costing a room, since the openings are fixed by the building and the wall run is what you are choosing.
Turning area into materials
Emulsion covers roughly 10–12 m² per litre per coat on a sealed surface. At 25 m², one coat takes about 2.3 litres and two coats about 4.6, so a 5-litre tin is the sensible purchase and leaves a little for touch-ups. New plaster absorbs far more — budget twice the paint, or seal it first.
Wallpaper is sold by the roll and the roll count depends on pattern repeat, not just area. Use the net figure for the area check, then confirm the roll count against the drop length: a 3 m wall needs three drops per roll only if the roll is 10 m and the repeat is small.
Tiling is the same idea with a waste allowance. Add 10% for a straight lay and 15% for a diagonal or herringbone pattern; the offcuts are real, not an accounting fiction.
What is not included
Ceilings, skirting boards, reveals and the window returns are separate surfaces. A door opening measured as 2 m² is the panel only; the frame and the architrave around it add a narrow strip that painters charge for by the metre. Cornicing and coving are linear, so measure them separately.
For a whole room, run one wall at a time and add the results rather than multiplying a perimeter: openings are rarely distributed evenly, and a wall of glass behaves very differently from a solid one.
Frequently Asked Questions
How much wall area does a 10 by 3 metre wall have?
30 m² gross. Removing 2 m² of doors and 3 m² of windows leaves 25 m² net.
Should openings be measured or counted?
Measured. The inputs are areas in square metres, so a standard door is about 1.8–2 m² and a standard window 1–2 m².
How much paint for 25 m²?
About 2.3 litres per coat at 10–12 m² per litre, so roughly 4.6 litres for two coats. Buy a 5-litre tin.
Does the tool include the ceiling?
No. It computes wall surface only. Measure the ceiling separately using the room length and width.
How much tile waste should I allow?
10% for a straight lay and 15% for diagonal or herringbone. Cutting around sockets and corners is where the extra goes.
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