Paint Calculator

A worked example

With the calculator’s starting values (wall area: 60 m²; number of coats: 2 coats; paint type: Emulsion (walls)), it returns:

• Paint required: 17.1 L (60 m² × 2 coats ÷ 7 m²/L)
• Buy (round up): 20 L (in 5 L units)
• Estimated applied cost: R 3 000 (R 50/m² for 2 coats)

How the calculator works

It multiplies the wall area by the number of coats and divides by a spreading rate of about 7 m² per litre per coat, which is typical for emulsion on smooth plaster. It then rounds the order up to 5-litre units and prices the job at a benchmark applied rate for labour and material.

Measuring the area

For a room, add the lengths of the walls and multiply by the ceiling height, then deduct the doors and windows. A standard door takes out about 1.7 m². Measure ceilings separately: the area is the floor area of the room. For exterior walls, measure each elevation and deduct the openings; include boundary walls if they are being painted too.

Rough surfaces such as bagged brick or textured plaster use considerably more paint than smooth plaster. For those, work at the low end of the spreading rate or add 20 to 30% to the litres.

Getting the system right

• New plaster: let it dry out properly, then apply an alkali-resistant plaster primer before the topcoats.
• Previously painted walls in good condition: wash, fill cracks, sand glossy areas and apply two topcoats.
• Chalky or powdery exterior walls: apply a stabilising primer first, or the new paint will peel.
• Wood and metal: use an appropriate primer and an enamel or water-based enamel topcoat.
• Damp walls: find and fix the cause of the damp first. Paint will not stop rising damp or a leak.

Labour and material

On most repainting jobs, preparation takes as much time as painting. That is why quotes vary so much: a painter who fills, sands and primes properly will cost more and last longer. Ask what preparation is included, how many coats, and which product, and compare quotes on that basis rather than on the total alone.