How Much Paint Do I Need? A Practical Guide for Kenyan Homes

The answer depends on three things you can find out before buying anything: how much wall there is, how many coats it needs and how far the paint goes on that surface. This guide works through each one using the same method as the FinishGrid Paint Calculator.

The paint formula

Because coverage is a range, the answer is a range too. FinishGrid buys for the poorer end of the range, so you are less likely to run short, and does not add a hidden percentage for waste.

Step 1: Measure the wall area

Measure walls, not floor. For each room, add up the length of every wall and multiply by the wall height: 2 × (length + width) × height. A 4 m × 3.5 m bedroom with 2.7 m walls has 2 × (4 + 3.5) × 2.7 = 40.5 m² of wall. Ceilings are measured separately as length × width (14 m² for the same room) because ceiling paint covers differently. A home with 150 m² of floor does not have 150 m² of wall to paint.

Step 2: Doors and windows

Take off doors and windows only if you have measured them: width × height × how many. In the bedroom, a 0.9 × 2.1 m door and a 1.5 × 1.2 m window come to 3.7 m², leaving 36.8 m² to paint. FinishGrid does not assume standard door or window sizes. If you skip this step, you simply plan a little more paint: without the deduction the same bedroom needs about 5.7–6.8 L instead of 5.2–6.2 L.

Step 3: Coverage per litre

Coverage is the area one litre covers in one coat. It is printed on the product's technical data sheet, and it is always better on smooth, sealed surfaces than on rough or absorbent ones, because a porous wall soaks up paint. These are the planning ranges FinishGrid uses when you don't enter your product's own figure:

These are planning ranges based on Kenyan manufacturers' technical information (the exterior figures are provisional FinishGrid planning records), not promises for any one product. If your paint states a different coverage, use that instead: the Paint Calculator lets you enter it.

Step 4: Number of coats

• Sound, previously painted walls in a similar colour: two finish coats.
• New smooth plaster, skimmed walls or walls that needed preparation: one preparation coat, then two finish coats.
• Ceilings: two finish coats on a sound painted ceiling; a preparation coat first on a new or prepared one.
• Changing to a very different colour: an undercoat may be needed for even coverage.

If the preparation coat is a thinned coat of emulsion, the water you add is not paint you buy: quantities are litres of paint as purchased. Which surfaces need which coats is explained in the complete project guide.

Step 5: Extra for waste

Many rules of thumb quietly add 10% or more for waste. FinishGrid doesn't: its default allowance is 0%, because the range already plans for the poorer coverage, and buying whole packs usually leaves a little over. If you want a margin for spills, touch-ups or a very absorbent surface, add it openly: the Paint Calculator accepts an allowance of up to 25%, added on top of the calculated quantity.

Step 6: Buying 20 L, 4 L and 1 L packs

Paint is sold in packs, commonly 20 L, 4 L and 1 L. FinishGrid picks the combination with the smallest total volume that still covers the requirement, and the fewest packs among equal options. That is why the bedroom's 5.2–6.2 L becomes 1 × 4 L + 3 × 1 L (7 L) rather than two 4 L tins (8 L). Buy the whole job's paint at once where you can, so the colour matches across tins.

Worked examples

Common mistakes

• Using floor area instead of wall area. The two are rarely the same.
• Forgetting the preparation coat on new or prepared walls.
• Using one coverage for every surface. Rough plaster and ceilings use more paint than smooth painted walls.
• Counting thinning water as paint. It isn't paint you buy.
• Adding a hidden waste percentage on top of a cautious estimate, then buying far too much.
• Buying one tin at a time. Colour can vary between batches.

Frequently asked questions