Is the ceiling area the same as the floor area?

For a flat ceiling, yes: the room's length × its width. Nothing is taken off for a loft hatch or a light fitting.

Can I use the wall paint on the ceiling?

If its tin says it suits ceilings, yes. If it is the same product and colour as the walls, add the two litre figures together before rounding to tins.

Painting a ceiling: how much paint and what else to buy

A flat ceiling has the same area as the floor, so multiply the room’s length by its width and work the paint out as for a wall: area × coats ÷ coverage, plus a little extra. A 4.2 m × 3.6 m ceiling is 15.12 m² and, at two coats and 10 m² per litre, needs about 3.3 L with 10% extra, plus an extension pole, a roller sleeve kept for the ceiling paint and sheets over the whole floor.

The ceiling area

Measure the room at floor level, wall to wall, in both directions.
Multiply: 4.2 × 3.6 = 15.12 m².
Take nothing off for a loft hatch, a roof light or a light fitting. The difference is small, and in the safe direction.
In an L-shaped room the ceiling is the floor area of the L; see floor area of an L-shaped room.

Ceiling paint is its own line

Walls and ceilings are usually different paints, so BuildBatch keeps them apart and never adds them together. If you are using the same product in the same colour for both, add the two litre figures before rounding to tins, and you may save a tin.

The coverage and the number of coats come from the tin. Two coats is the starting figure; a stain, a strong colour change or new plaster can change it.

Worked example

The example room’s ceiling, at the example figures:

Ceiling area: 4.2 × 3.6 = 15.12 m²
Two coats: 15.12 × 2 = 30.24 m² of coating
At 10 m² per litre: 30.24 ÷ 10 = 3.024 L
Plus 10%: 3.024 × 1.1 = 3.326 L

In 2.5 L tins only, that is 1.33 tins, so 2 tins and 5 L, about 1.67 L over. If your ceiling paint also comes in 1 L tins, a 2.5 L tin and a 1 L tin make 3.5 L, about 0.17 L over.

The coverage figure matters most. At 12 m² per litre the same ceiling needs 2.772 L: still just more than one 2.5 L tin, so the same two tins.

What a ceiling adds to the list

An extension pole, so you can roll from the floor rather than from steps.
A roller sleeve for the ceiling paint, separate from the wall paint’s, so neither has to be washed out between them.
A tray, and a brush for cutting in along the edges and round fittings.
Dust sheets over the whole floor, 15.12 m² here, not just along the walls: paint spatters down from a roller overhead.
Eye protection, for the same reason.
Masking tape, if you are not repainting the walls. The ceiling meets them along the 15.6 m perimeter; rolls are commonly 25 m or 50 m.
Caulk, if the joint between the walls and the ceiling has cracked. The tube says how far it goes.

Before you start

Paint the ceiling before the walls, so drips and spatter land on walls you have not painted yet.
Brush off dust and cobwebs, wash down, and fill cracks as you would on a wall.
A stain from an old leak needs its cause fixed and a stain-blocking primer before any emulsion.
Textured ceiling coatings applied before 2000 can contain asbestos. Do not sand or scrape a coating you are not sure about; get advice first.

Do it with BuildBatch

Open the Room Refresh Batch with paint chosen and make sure Ceiling is ticked. It works out the ceiling paint in whole tins from the sizes you enter, separately from the walls, and puts the extension pole and a sleeve for each paint on the list.

What this guide does not cover

Sloping ceilings, dormers and stairwells, where the area is not the floor area and the height needs proper access equipment. Light fittings beyond cutting in round them: taking one down is electrical work. Coving and ceiling roses. Removing a textured coating.