How Much Putty per m²: Skim Coat Consumption for Walls and Ceilings

Short answer: the calculator uses 1.5 kg of putty per m² for two coats, in 25 kg bags. For 50 m² that is 75 kg, so 3 bags; one 25 kg bag covers about 16.7 m² in two coats. A 4 × 5 m room with the ceiling (63.3 m² net) needs 95 kg, so 4 bags.

Consumption per coat and for two coats

The calculator assumes two thin coats of putty and uses 1.5 kg/m² for them. It does not count the coats separately, so 0.75 kg/m² is only an average per coat, not a manufacturer's figure. If you apply one coat or three, check the consumption per coat and the number of coats on your putty's data sheet and scale the quantity proportionally.

How to calculate putty for a room

Putty is calculated on the net area: walls (perimeter × height) minus doors and windows, plus the ceiling if you skim it. Multiply that area by 1.5 kg/m², round the result up to a whole kilogram, then divide by 25 and round up to whole bags. The calculator does this for each room and adds them up.

Example: a 4 × 5 m room, height 2.6 m, a 2 m² door and a 1.5 m² window. Walls 43.3 m², ceiling 20 m², total 63.3 m². Putty 63.3 × 1.5 = 94.95, so 95 kg or 4 bags (100 kg). Without the ceiling: 43.3 m², 65 kg, so 3 bags.

Table: how much putty by area

Quantities are calculated as in the calculator: 1.5 kg/m² for two coats, with kilograms and 25 kg bags rounded up.

Area (m²)	Putty (kg)	Bags of 25 kg
10	15	1
20	30	2
30	45	2
40	60	3
50	75	3
60	90	4
80	120	5
100	150	6
150	225	9

Putty and joint filler on plasterboard

With the Drywall (Plasterboard) option the calculator does not change putty consumption; instead it adds a separate Joint Filler item by finish level: Q1 – Basic 0.25 kg/m², Q2 – Standard 0.4 kg/m², Q3 – Fine 0.6 kg/m², in 25 kg bags. For 50 m² of plasterboard that is 13 kg for Q1, 20 kg for Q2 and 30 kg for Q3 (1, 1 and 2 bags).

If the Putty option is also switched on, the calculator additionally counts 1.5 kg/m² of putty on the same area. If you finish the boards with joint filler only, up to level Q3, switch the Putty option off so you don't buy material twice.

What changes actual consumption

Unevenness: every dip or wave in the wall means a thicker coat and more material than average.
Substrate absorption: a dry, dusty or unprimed substrate draws water out of the putty and makes it harder to spread.
Hand or machine application: machine-applied putty has its own consumption, given in the manufacturer's instructions.
Coat thickness: consumption rises in proportion to thickness, so follow the manufacturer's instructions for your product.
Ready-mixed paste and dry powder in bags do not have the same consumption per m².

Common skimming mistakes

Using putty as a levelling compound: thicker layers and larger unevenness need a levelling compound or plaster, with putty only as the finishing coat.
Applying the second coat before the first is dry, which causes cracks.
Sanding without checking with a light held at an angle, so unevenness only shows after painting.
Mixing more putty than you can use before it starts to set.
Buying exactly the calculated amount with no small reserve for corners and repairs.

Frequently asked questions

How much putty per square metre?

The calculator uses 1.5 kg per m² for two coats, which is 0.75 kg per coat on average. Check your product's exact consumption in the manufacturer's instructions.

What area can you skim with one 25 kg bag?

At 1.5 kg/m² for two coats, one 25 kg bag covers about 16.7 m².

How many bags of putty for a room with a 20 m² floor, ceiling included?

For a 4 × 5 m room, 2.6 m high, with a 2 m² door and a 1.5 m² window, the net area is 63.3 m². That is 95 kg of putty, so 4 bags of 25 kg.

Can I use putty to level out larger unevenness?

No. The 1.5 kg/m² figure applies to thin finishing coats; level out thicker unevenness first with a levelling compound or plaster.

Open the calculator: Paint, Putty & Plasterboard