Mural paint calculator: how much paint a wall mural needs

The calculator above opens with a sample wall in feet and gallons. Type in your own width and height, subtract any windows, doors or vents you will not paint, then set the coats of primer and base colour and how much of the wall the design will cover. The box that matters most is coverage: copy it from the label or technical data sheet of the paint you are actually buying. If your tins are sold in litres, switch to metric and enter the label's figure in square metres per litre.

How the calculation works

Every layer is treated the same way. The tool takes the area that layer covers, multiplies it by the number of coats, divides by how far one unit of paint spreads, and adds a margin for paint that never reaches the wall. Primer and base colour usually cover everything; a geometric design might leave a third of the base showing.

For each layer:

1. Paintable area = wall width × wall height, minus openings.
2. One coat = area × the share of the wall that layer covers ÷ coverage per coat.
3. Multiply by the number of coats.
4. Add the waste margin by multiplying by (1 + waste).
5. Round primer and base up to whole cans, and add the three layers for the total.

As a single line: paint = area × coats × share ÷ coverage × (1 + waste).

A worked example with the starting figures

The defaults describe a modest wall, 20 feet wide and 10 feet high with no openings, so 200 square feet to paint. The paint is assumed to cover 350 square feet per gallon per coat, the waste margin is 10%, and paint comes in 1-gallon cans.

Primer is 200 ÷ 350, or 0.57 gallon, and the margin lifts it to 0.63: one can, with more than a third left for touch-ups. The base colour is the same. The design covers 140 square feet twice, 280 square feet in all, which is 0.80 gallon or 0.88 with waste. Together that makes 2.14 gallons. The design figure is shared between every colour in the sketch, so it becomes several smaller tins rather than one can.

Replace the assumptions with your own figures

• Coverage: 350 is a round figure for the example, not a property of mural paint. Read your own can or data sheet. Labels often give a range, and rough render, brick and bare concrete soak up paint, so use the low end there.
• Coats: One coat each of primer and base is optimistic on a patched or dark wall. Pale colours over dark ones, and some yellows and reds with weak hiding power, often need another pass.
• Design share: Look at your sketch and estimate how much of it is design colour rather than background.
• Waste: 10% covers what stays in trays, rollers and tins. Raise it for textured walls or a community painting day with many hands and many brushes.
• Can size: Change it to five-gallon pails or to whatever litre sizes your supplier stocks.

The surest coverage figure is your own. Paint a measured patch at the start of the job, note how much went on, and type that number in.

What the calculator does not know

It assumes a flat wall, and rough brick or ribbed cladding has more surface than width × height suggests. It also treats the design as one block of paint. To split it by colour, run the calculator once per colour with primer and base set to zero and the design share set to that colour's portion of the wall.

Spray paint is counted by the area one can covers, so use the figure on the can. Protective layers can be estimated here too: set primer and base to zero, the design share to 100%, and the coverage and coats to what the clear coat or anti-graffiti product's data sheet gives. The section on coatings in how a large mural gets made explains why that last layer is worth the trouble.

Practical advice from mural work

Mix each custom colour in one batch, enough for the whole wall plus spare, because a second batch rarely matches exactly. Label the leftovers with the wall and the date: saved base colour will patch a tag years later. Check the minimum application temperature on the data sheet before you book the dates.

Before you open a gallon, test colours small. Student acrylics on scrap board show whether two colours fight before you have rolled a wall in them, and paint markers do the same for line work on a practice panel. On the wall, a telescopic pole saves most of the ladder work on base coats, and a pack of flat and angled brushes handles edges and cutting in. When the quantities are settled, carry them into the mural price calculator as your materials line, and lay out the design with the mural grid calculator.

These picks come from maker details and published reviews rather than our own testing.

Questions

How much paint do I need for a 200 square foot mural?

With one coat of primer, one base coat and a design covering 70% of the wall in two coats, at 350 square feet per gallon plus 10% waste, about 2.14 gallons. Primer and base need one 1-gallon can each. If your can states a different coverage, enter it and the total changes.

Do I need to prime a wall before painting a mural?

It depends on the surface and the paint system, and the data sheet for your paint will say. New render, bare concrete and powdery old paint usually need a primer or sealer. If your system does not call for one, set primer coats to zero.

How do I use a coverage figure in square metres per litre?

Switch the calculator to metric and enter the wall in metres. Type the label's square metres per litre straight into the coverage box. Results then come out in litres, and you can set the container size to the tins your shop sells.

Why did I run out of paint when the calculator said I had enough?

Usually because the wall took more paint than the label promised. Porous or textured surfaces, thinning, an extra coat on a stubborn colour and spills all add up. Measure your own coverage on a test patch and raise the waste margin on the next wall.