Free paint calculator. Litres required per coat for walls, ceilings, and trim with NZ surface coverage rates.
This calculator estimates the litres of paint a room's walls take, and turns that into 4 litre and 10 litre tins. Give it the room dimensions, the wall height, the number of doors and windows, and how many coats you are putting on.
Wall area is the room perimeter — twice the length plus the width — multiplied by the wall height. Doors are deducted at 1.8 square metres each and windows at 1.4 square metres each, and the result is floored at zero so an over-deduction cannot produce a negative area.
That net area is then multiplied by the number of coats, divided by the spread rate, and 10% is added for wastage.
The wall height defaults to 2.4m, which is the standard stud height here, but it is an input — set it to what you measured.
The page works at 10 square metres per litre. That is a single round figure applied to every surface, and it is the number on this page most worth replacing with your own.
Real spread rate moves a long way with the product and what it is going onto. A sealer on bare plasterboard, a topcoat on a previously painted wall, and an exterior coat on rough-sawn weatherboard do not cover the same area per litre, and the tin states the manufacturer's figure.
Treat the litres here as a starting point for an order, then check it against the spread rate printed on the product you are actually buying.
Spread rate, the number of coats and the preparation a surface needs are product and site decisions. Check the tin's stated spread rate and confirm the system with your paint supplier before you order.