How much paint for a room? Worked examples at 10, 20, 50 and 100 m²

From square meters to litres, then to cans

litres = area × coats ÷ coverage · with reserve = litres × (1 + reserve ÷ 100) · cans = rounded up (litres with reserve ÷ can size)

The area in the table is net wall — what the roller actually crosses, with doors and windows already deducted. If you are painting the ceiling too, add its area before you use this table.

Look at the “left over” column: it is the real reason the arithmetic pays off. At 100 m² only half a litre is left, at 10 m² almost a third of a litre — but at 50 m² a litre and a half sits unused, because five cans carry 12.50 L for the 11 L you need.

All four rows use the same assumptions: two coats, a coverage of 10 m²/L, a 10% reserve and a 2.5 L can. Those are examples, not rules — all four values stay editable in the calculator.

How to calculate wall area for painting — with doors and windows deducted →

Why one extra square meter can cost a whole can

Litres rise smoothly, but buying happens in steps. That is why there is almost no difference in paint between 34 and 35 m², yet a whole can of difference on the receipt: 34 m² needs 7.48 L and fits into three cans with just 0.02 L to spare, while 35 m² needs 7.70 L and pushes you into a fourth can with 2.30 L left over.

The same thing repeats roughly every 11 m²: between 45 and 46 m² you go from four cans to five, and between 56 and 57 m² from five to six. When you land right on the edge, as at 34 m², do not rely on that 0.02 L — it is less than a glass of paint and disappears on the first touch-up.

The practical rule: if your figure lands just under a threshold, either measure the room again more carefully or raise the reserve. A small measuring error there does not cost decilitres, it costs a whole can.

The can size changes how many litres you carry home

The amount you need does not depend on the packaging, but the amount you buy does. At 20 m² one 5 L can and two 2.5 L cans both give you 5 L — except the first is one container instead of two. At 50 m² it goes the other way: five 2.5 L cans carry 12.50 L, three 5 L cans carry 15 L, so 2.5 L more than needed.

At 100 m² the same logic gives 22.50 L in small cans against 25 L in large ones. Bigger packs are usually cheaper per litre, so it is worth comparing both scenarios: sometimes buying more paint in a larger tin is cheaper, sometimes it is pure waste.

Small 0.75 L cans are a third case. At 10 m² three of them give 2.25 L with only 0.05 L to spare — the tightest possible fit, but also three lids and three chances for the shade not to match. Ideal for touch-ups, rarely for a whole room.

What the reserve actually buys

The reserve exists for touch-ups, spatter and that last corner that always asks for a little more. Around ten percent is the usual plan, but that is a purchasing convention, not a rule — the field is free.

At 50 m² you can see exactly what it costs. Without a reserve you need precisely 10 L, which is four 2.5 L cans and nothing left over. With a 10% reserve you need 11 L, so five cans. Raise the reserve to 15% and you need 11.50 L — still five cans. In other words, the first percent of reserve buys a whole can there, and the next five are free.

So do not set the reserve blind: enter 0, then 10, then 15, and see where the can count changes. If it does not change, take the larger reserve — it costs you nothing.

These numbers only hold at your coverage

Everything in this article rests on a coverage of 10 m²/L, chosen because it is a round number, not because it is typical. The real coverage is printed on the label and differs from product to product, and a rough, absorbent or never-painted wall lowers it further.

So take your own figure from the tin before you buy and, if the wall is in poor shape, be conservative. Exactly how far coverage and coats move the result is broken down in a separate guide.

One coat or two? How coverage and wall condition change paint consumption →

Run your own room

Open the calculator with the 50 m² row already filled in, then change the area, coverage, coats, reserve and can size to your own values. The result shows the litres, the number of cans and how much paint is left.

If you do not know your area yet, enter the room dimensions and the openings first — the calculator works out the net wall itself, and you continue from there.

Open the paint calculator with the 50 m² example →