Net wall area
Wall area = 2 × (length + width) × height − door and window area.
Net wall area. Wall area = 2 × (length + width) × height − door and window area.
Where:
- A
- Net wall area
- L
- Length
- W
- Width
- H
- Height
- O
- Openings deducted
Paint Calculator
Work out how much paint you need for walls and ceilings. Add rooms, subtract doors and windows, and estimate tins and painting costs.
Your painting project
Currency changes the price label only; it does not convert prices. Enter your own local prices, including any applicable tax.
Rooms and openings
Up to 20 rooms and 20 opening groups per room.
Paint and purchase options
Use the coverage on your paint label. Walls and ceilings are estimated and purchased separately; tins are pooled across rooms for each paint type.
Optional painting costs
Enter a rate for the whole job per unit of painted surface, not per coat or floor area. Wall and ceiling areas are counted once.
Room-by-room breakdown
| Rooms and openings | Gross wall area | Openings deducted | Net wall area | Ceiling area |
|---|---|---|---|---|
| Room 1 | 35 m² | 3.24 m² | 31.76 m² | 0 m² |
How much paint do I need?
- Enter each rectangular room’s length, width and height. Add the doors and windows you will leave unpainted, and include ceilings where needed.
- Set the coats, coverage per coat, tin size and price for wall and ceiling paint. Choose an extra allowance for waste and touch-ups.
- Review the paint quantities and whole tins to buy. Add your labour rate and preparation costs, then copy a link to share the estimate.
How the paint estimate is calculated
Ceiling area
Ceiling area = length × width, when included.
Ceiling area. Ceiling area = length × width, when included.
Where:
- B
- Ceiling area
- L
- Length
- W
- Width
Paint needed (including extra)
Paint volume = area × coats ÷ coverage × (1 + extra allowance ÷ 100).
Paint needed (including extra). Paint volume = area × coats ÷ coverage × (1 + extra allowance ÷ 100).
Where:
- V
- Paint needed (including extra)
- S
- Paintable area
- n
- Number of coats
- r
- Coverage per coat
- e
- Extra paint allowance (%)
Tins to buy
Tins = paint volume ÷ tin size, rounded up. Paint cost = whole tins × price per tin. Labour is added once per unit of net painted area.
Tins to buy. Tins = paint volume ÷ tin size, rounded up. Paint cost = whole tins × price per tin. Labour is added once per unit of net painted area.
Where:
- N
- Tins to buy
- V
- Paint needed (including extra)
- s
- Tin size
Paint purchase cost
Use the coverage on your paint label. Walls and ceilings are estimated and purchased separately; tins are pooled across rooms for each paint type.
Paint purchase cost = Tins to buy × Price per tin.
Where:
- C
- Paint purchase cost
- N
- Tins to buy
- p
- Price per tin
Estimated project cost
Enter a rate for the whole job per unit of painted surface, not per coat or floor area. Wall and ceiling areas are counted once.
Estimated project cost = Paint purchase cost (Wall paint) + Paint purchase cost (Ceiling paint) + Labour per painted area × (Net wall area + Ceiling area) + Other materials and preparation.
Where:
- T
- Estimated project cost
- C₁
- Paint purchase cost (Wall paint)
- C₂
- Paint purchase cost (Ceiling paint)
- R
- Labour per painted area
- A
- Net wall area
- B
- Ceiling area
- E
- Other materials and preparation
Worked painting examples
One room, walls only
A 4 m × 3 m room with 2.5 m high walls has 35 m² of wall area. After deducting a 1.8 m² door and a 1.44 m² window, 31.76 m² remains. With 2 coats, coverage of 10 m²/L and 10% extra, you need 6.99 L of paint: 3 tins of 2.5 L.
Add the ceiling
The same room adds 12 m² of ceiling. At 2 coats, 10 m²/L coverage and 10% extra, allow 2.64 L of ceiling paint. It is rounded into separate tins, so different wall and ceiling finishes are not mixed.
Prices are entered by you; example dimensions and coverage are illustrative, not local market rates.
Paint calculator questions
Should I subtract doors and windows?
Subtract openings you will not paint. Enter their actual width, height and quantity. For different sizes, add separate rows. Door frames, skirting boards and trim need their own estimate.
How many coats and how much extra paint should I allow?
Follow the paint manufacturer’s instructions. Two coats and 10% extra are starting assumptions, not a guarantee. Rough or porous walls and large colour changes can require different coverage or more coats. Primer is not included.
Can I calculate the cost of painting a room?
Yes. Enter the price and size of each paint tin, a labour rate per unit of painted surface, and other preparation costs. The total includes rounded-up tins rather than just the exact liquid used. Enter tax-inclusive prices if you want tax included.
Does the calculator include ceilings and irregular rooms?
Ceilings are optional for each rectangular room and use separate paint settings. For irregular spaces, measure and estimate their surfaces separately. Do not split a room into rectangles unless you account for imaginary internal walls. Sloping ceilings and exterior walls are not modelled.
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About this tool
Published by Online Tools CenterLast updated:
Check the units, assumptions and rounding before using a result. Health and financial estimates are educational and do not replace individual professional advice.
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