Why did I run out despite following the tin?

Tin coverage assumes a smooth, sealed, primed surface. Fresh plaster absorbs heavily and can take fifty percent more on the first coat, which is what the wastage allowance is for.

Construction & Homefinishing

Paint Quantity Calculator

Paint quantity from wall area, coverage and coat count. Coverage varies by a factor of two between a smooth sealed wall and fresh plaster, which is why it is an input rather than a constant.

Also called: how much paint do i need, paint coverage.

Paint (litres)

2.2

2.2 litres for 20 m² over 1 coat(s), including 10% wastage.

Area after deductions (m²)

Area across all coats (m²)

Before wastage

Area one unit covers (m²)

How this is calculated

Method and background

How this is calculated

Area times coats, divided by the coverage the tin claims, plus wastage. The claimed coverage is measured on a smooth sealed surface; fresh plaster, textured render or a strong colour change all drink far more. The first coat on new plaster can take half again as much as the tin says, which is the single most common reason a job runs short.

quantity = area * coats / coverage per unit, plus wastage

A: Net area (m2)
c: Coats (count)
r: Coverage per unit (m2)
s: Wastage (decimal)

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

a room at two coats

Length (m): 12
Width or height (m): 3
Or enter the area directly (m²): 0
Openings to deduct (m²): 4
Coverage per litre (m²): 10
Coats or layers: 2
Wastage: 10%

Paint (litres)7.04

Worked by hand at each step

Open this example

poor coverage doubles the paint

Length (m): 12
Width or height (m): 3
Or enter the area directly (m²): 0
Openings to deduct (m²): 4
Coverage per litre (m²): 5
Coats or layers: 2
Wastage: 10%

Paint (litres)14.08

boundary: the input that matters most

Open this example

Method and limits

What it assumes

Coverage as stated on the tin, which assumes a prepared surface.

What it deliberately does not model

A dark colour under a light one often needs a third coat regardless of the arithmetic.
Rollers waste more than brushes; spraying wastes more than both.

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Frequently asked questions

Why did I run out despite following the tin?: Tin coverage assumes a smooth, sealed, primed surface. Fresh plaster absorbs heavily and can take fifty percent more on the first coat, which is what the wastage allowance is for.