Paint Calculator
Work out how much paint a wall or room needs, allowing for coats, openings and the coverage rate on the tin.
Formula
Net area × number of coats ÷ coverage rate, plus wastage.
- Net area (m²) = Total area − openings
- Paint (L) = Net area × Coats ÷ Coverage (m²/L) × (1 + wastage % ÷ 100)
- Tins = ceiling( Paint ÷ Tin size )
Worked example
60 m² of wall with 4 m² of openings, two coats, coverage 11 m²/L, 5 litre tins, 10% wastage.
- Net area = 60 − 4 = 56 m²
- Area over two coats = 56 × 2 = 112 m²
- Paint = 112 ÷ 11 = 10.18 L
- With 10% wastage = 11.2 L
- Tins = 11.2 ÷ 5 = 2.24, so 3 tins
About 11.2 litres — three 5-litre tins.
Assumptions and limitations
- Coverage is the manufacturer figure for the specific product and surface. Different products vary widely and the same product varies with the substrate.
- The first coat on bare or porous surfaces uses noticeably more than later coats. If you know that, run the coats as separate calculations.
- Openings are deducted at face value. Painters often ignore small openings because cutting in around them consumes paint regardless.
- No allowance is made for primer, sealer or a mist coat unless you calculate those separately.
What this calculator does not do
- Does not select the product or the system. Primer, undercoat and topcoat requirements come from the manufacturer's specification for the substrate.
- Does not allow for surface preparation, filling or making good, which can change how much the first coat absorbs.
- Does not calculate the wall area itself. Enter the area you have measured, with openings entered separately.
Practical tips
- Buy all tins of a colour from one batch. Batch-to-batch colour variation is visible on a large wall even when the code is identical.
- Keep a small amount of each colour for touch-ups after the job. Matching later is far harder than it sounds.
- On new plaster, a thinned mist coat is normally needed first. It has completely different coverage and should be calculated on its own.
Frequently asked questions
How much paint do I need for a room?
Add the areas of all four walls, deduct the doors and windows, multiply by the number of coats, and divide by the coverage rate on the tin. Add around 10% for wastage and touch-ups.
How many square metres does a litre of paint cover?
Commonly 10–14 m² per litre for emulsion on a smooth sealed surface, but the tin is the authority. Porous, textured or heavily contrasting surfaces achieve considerably less.
Do I need two coats?
Usually, and often three when covering a dark colour with a light one. A single coat rarely gives even colour on anything other than a repaint in a similar shade.
Should I subtract windows and doors?
Deduct the larger ones. Many painters ignore openings under about 1 m², because the extra cutting-in around them uses roughly as much paint as the area saved.
Related calculators
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- Tile Calculator Calculate how many tiles a floor or wall needs, including grout joints and a cutting allowance.
- Area Calculator Calculate the area of a rectangle, triangle, circle or trapezoid, with results in metric and imperial units.
- Brick & Block Calculator Calculate how many bricks or blocks a wall needs, including walls more than one unit thick, along with the mortar between them.
Estimating tool, not a design. This calculator works out quantities from the dimensions you enter. It does not size any structural member, verify a design, or confirm compliance with any building code. Check every result against your project specification and applicable local standards, and involve a qualified engineer where the work requires one.