Plaster Calculator
Plaster area and quantity for a wall, ceiling or surface, with opening deduction and wastage %.
Paint Calculator
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Paint litres required for a wall, ceiling or surface, with opening deduction, coats and wastage %.
Length of the wall, ceiling, or surface to paint, in the unit chosen above.
Height for a wall, or width for a ceiling or general surface, in the same unit.
Total door/window/opening area to deduct from one surface, in the unit's own squared area (for example m² if the unit is m). Defaults to 0.
A whole number of paint coats. Defaults to 2.
Area one litre of paint covers, in the unit's own squared area (for example square metres per litre if the unit is m, or square feet per litre if the unit is ft). Check your paint tin's label for this figure.
An adjustable allowance for spillage, extra coats on edges, and touch-ups, from 0 to 50%. Defaults to 10%.
A whole number from 1 to 1,000,000, for identical walls, ceilings, or rooms.
Result
Enter the values above to see the result.
How to use
This paint calculator works out how much paint you need for a rectangular wall, ceiling or general surface — a practical wall paint calculator and paint quantity calculator for homeowners, painters, and contractors planning a paint job.
- Choose the unit your measurements are in.
- Enter the surface's length and height/width.
- Enter an opening deduction area (doors, windows), if any — it defaults to 0.
- Enter the number of coats (defaults to 2) and the coverage per litre your paint achieves in the selected unit's own squared area (defaults to 10, meaning 10 square metres per litre if the unit is metres).
- Enter a wastage percentage for spillage and touch-ups (defaults to 10%, up to 50%), and the number of identical surfaces (defaults to 1).
- Read the total paint litres required (including wastage), and the working. Copy or print the result.
Method
- Gross area = length × height/width (per surface), × the number of identical surfaces for the total.
- Net paintable area = gross area − opening deduction area. Enter the opening area (doors, windows, or any unpainted section) for one surface — this paint area calculator deducts it once per surface, then multiplies by the number of identical surfaces you entered. An opening area that equals or exceeds one surface's gross area is rejected, since there would be nothing left to paint.
- Coated area = net paintable area × number of coats. Most walls need at least two coats for even colour — this room paint calculator and ceiling paint calculator defaults to 2, but you can enter any whole number of coats.
- Paint litres before wastage = coated area ÷ coverage per litre. Coverage per litre is always entered as area per litre in the unit you selected — for example, square metres per litre if the unit is metres, or square feet per litre if the unit is feet. Check your paint tin's label for its own coverage figure and enter it directly; this tool does not implement brand-specific or country-specific coverage standards.
- Total paint litres required = paint litres before wastage × (1 + wastage %). The wastage percentage is an adjustable allowance for spillage, extra coats on edges and corners, and touch-ups. 10% is a common starting allowance and this calculator's default; some surfaces or techniques call for more.
Unit conversions are exact: 1 mm = 0.001 m, 1 cm = 0.01 m, 1 inch = 0.0254 m and 1 foot = 0.3048 m. The same unit selector applies to every dimension, the opening area, and the coverage figure — there is no mixing of units within one calculation. Area and paint litres are both displayed rounded to 2 decimal places.
This paint quantity calculator estimates paint litres only, for a flat rectangular surface. It does not calculate primer, putty, or labour, brand-specific paint recommendations, cost, colour matching, multi-room totals, a PDF report, Excel export, or a bill of quantities (BOQ).
Worked example
A 5 × 4 m wall, 2 m² opening, 2 coats, 10 m²/litre coverage, 10% wastage, 1 surface:
| Input | |
|---|---|
| Unit | m |
| Surface length | 5 |
| Surface height/width | 4 |
| Opening deduction area | 2 |
| Number of coats | 2 |
| Coverage per litre | 10 |
| Wastage % | 10% |
| Number of identical surfaces | 1 |
| Result | |
| Total paint required (incl. wastage) | 3.96 |
| Paint required before wastage | 3.60 |
| Net paintable area | 18.00 |
| Gross area | 20.00 |
| Opening deduction area | 2.00 |
| Coated area (area × coats) | 36.00 |
| Number of coats | 2 |
| Coverage per litre | 10 |
| Wastage % | 10% |
FAQ
How do I calculate how much paint I need?
Enter the surface's length and height/width, an opening deduction if any, the number of coats, and your paint's coverage per litre. This paint litres calculator deducts the opening, multiplies by the number of coats, then divides by the coverage figure to give litres before wastage.
Is the result an estimate?
Yes. This is an estimation aid for planning and quantity checks, not a final billing quantity. Actual paint usage may vary due to surface texture and porosity, application method, paint brand and type, and site conditions — verify surface area, coats, coverage, and wastage before purchase or application, and confirm the final figures with a licensed engineer, architect, contractor, or professional painter.
Do I need to sign up?
No. This paint area calculator works without an account, sign-up, or login.
Does this use AI?
No. This tool is a deterministic calculator — the same inputs always give the same result, with no AI involved.
Does this include primer, putty, or labour?
No. This paint calculator estimates paint litres only. Primer, putty, and labour are separate calculations this tool does not perform.
Can I use this for a rectangular wall, ceiling, or flat surface?
Yes. The same length × width formula applies to a wall paint calculator, a ceiling paint calculator, or any flat rectangular surface — choose the surface's length and height/width as the two dimensions.
How much wastage should I add for paint?
10% is a common starting allowance for spillage and touch-ups, and is this calculator's default; some surfaces or techniques call for more. Always confirm your own project's expected wastage.
What if my opening area is larger than the wall?
This paint wastage calculator rejects an opening area that equals or exceeds the surface's gross area, since there would be nothing left to paint — check your dimensions and opening size.
Does it calculate paint cost?
No. This calculator estimates paint quantity only, not material or labour cost.
Can I calculate paint for multiple identical rooms at once?
You can enter a number of identical surfaces to multiply a single surface's result, but this tool does not save or total multiple different rooms — enter and read one surface calculation at a time.
References
- Rectangular area and paint-coverage ratio: (length × width − opening) × coats ÷ coverage per litre (general geometry).
- International yard and pound agreement (1959): 1 inch = 25.4 mm and 1 foot = 304.8 mm exactly.