One of the most common questions we get at Kasha Paints is: "How much paint do I need?"

Buy too little and you're making an emergency run mid-project (and risking a colour mismatch between batches). Buy too much and you've got leftover tins cluttering your store. Either way, you're wasting money.

This guide gives you a simple, reliable formula to calculate paint quantities for any room — plus ready-made estimates for common Nigerian room sizes.

Hero image: Person measuring a wall with a tape measure, paint tins in the foreground

The Basic Formula

The calculation is straightforward:

Litres needed = (Total wall area (m²) x Number of coats)/Coverage rate (m²/litre)

Let's break each part down.

Step 1: Calculate Total Wall Area

For a rectangular room, measure:

Length of each wall (in metres)
Height of the walls (floor to ceiling)

Formula for a rectangular room:

Wall area = 2 x (L + W) x H

Where:

L = room length
W = room width
H = ceiling height (typically 3 metres in Nigerian buildings)

Example: Standard 4m × 4m Room

Subtract Doors and Windows

Don't pay for paint you won't use. Subtract:

Standard door ≈ 1.8 m² (0.9m × 2.0m)
Standard window ≈ 1.2 m² (1.2m × 1.0m)
Sliding glass door ≈ 3.6 m² (1.8m × 2.0m)

For the 4m × 4m room with 1 door and 2 windows:

Paintable area = 48 - 1.8 - (2 x 12) = 43.8 m²

Image: Diagram showing wall measurement technique — length, width, height labelled with arrows

Step 2: Know Your Coverage Rate

The coverage rate tells you how many square metres one litre of paint will cover. This varies by paint type:

Paint Type	Coverage Rate	Notes
Emulsion (water-based)	8–12 m²/litre	Most common for walls
Satin / Silk emulsion	10–14 m²/litre	Smoother, spreads further
Gloss / Oil-based	12–16 m²/litre	For woodwork and metal
Textured paint	3–6 m²/litre	Thick application
Primer / Undercoat	8–10 m²/litre	Sealing coat
Masonry / Exterior	6–8 m²/litre	Rougher surfaces absorb more

Important: These are _single coat_ coverage figures. The coverage rate is printed on every tin of paint — check the label for the specific product you're using.

Why the Range?

Coverage varies depending on:

Wall surface: Smooth plastered walls → higher coverage. Rough block walls → lower coverage.
Wall porosity: Primed/sealed walls absorb less paint than bare walls.
Application method: Roller typically uses less paint than brush. Spray uses most.
Paint colour: Dark colours over light surfaces may need extra coats for opacity.

Use the lower number in the range when estimating for bare/rough walls. Use the higher number for smooth, primed walls.

Step 3: Apply the Number of Coats

Situation	Coats Needed
Primer on new wall	1 coat
Same colour repaint	2 coats
Light over light colour	2 coats
Dark over light colour	2–3 coats
Light over dark colour	3 coats (or tinted primer + 2 coats)
Exterior walls	2–3 coats

Putting It All Together

Let's calculate for our 4m × 4m room (1 door, 2 windows) with standard emulsion:

Paintable area: 43.8 m²
Coverage rate: 10 m²/litre (mid-range, assuming primed walls)
Coats: 2

Litres needed = (43.8 x 2)/10 = 8.76 litres

Round up to 10 litres (you always want a small buffer for touch-ups).

That's two 4-litre tins + one 1-litre tin, or one 20-litre bucket (which will have leftover for future touch-ups).

Quick Reference for Common Nigerian Room Sizes

Here are pre-calculated estimates assuming 3m ceiling height, 1 door, 1 window per room, 2 coats of emulsion paint at 10 m²/litre coverage:

Room Size	Wall Area	After Openings	Paint Needed (2 coats)	Recommended Purchase
3m x 3m	36 m²	33 m²	6.6 L	2 x 4 L tins
3m × 4m	42 m²	39 m²	7.8 L	2 × 4L tins
4m × 4m	48 m²	44 m²	8.8 L	10L bucket
4m × 5m	54 m²	50 m²	10 L	10L bucket
5m × 5m	60 m²	56 m²	11.2 L	10L + 4L
5m × 6m	66 m²	62 m²	12.4 L	10L + 4L
6m × 6m	72 m²	68 m²	13.6 L	2 x 10L or 20L

Note: These are estimates. Your actual needs may vary depending on the wall surface, paint brand, and application method.

Calculating for an Entire Flat

For a standard 3-bedroom flat in Nigeria (typical layout):

Room	Size	Paint Needed
Living/dining room	5m x 6m	~12 L
Master bedroom	4m x 5m	~10 L
Bedroom 2	4m x 4m	~9 L
Bedroom 3	3m x 4m	~8 L
Kitchen	3m x 3m	~7 L
2 Bathrooms/toilets	2m x 2m each	~4 L each
Corridor	—	~5 L
Total		~59 L

With a 10% buffer for touch-ups: ~65 litres or roughly three 20-litre buckets + one 4-litre tin.

Ceiling Calculation

Don't forget the ceiling! The formula is simpler:

Ceiling area = Length x Width

For a 4m × 5m room: ceiling = 20 m²

At 10 m²/litre × 2 coats = 4 litres of ceiling paint.

Tip: Ceiling paint is usually a different product — it's formulated to be thicker (less drip) and is typically white. Don't use wall emulsion on ceilings.

Pro Tips for Accurate Estimation

1. Always Buy Extra

Add a 10–15% buffer beyond your calculation. You'll be glad when you need to do touch-ups months later. Paint batches can vary slightly in colour, so extra from the same batch is valuable.

2. Don't Forget the Primer

If painting new/bare walls, add primer quantities too: same wall area × 1 coat ÷ primer coverage rate.

3. Account for Colour Changes

Going from dark to light? You'll need 3 coats minimum, or use a tinted primer first. Factor this into your calculation.

4. Consider the Surface

Rough block walls: Use a lower coverage rate (8 m²/litre)
Smooth plastered walls: Use a higher coverage rate (12 m²/litre)
Previously painted, good condition: Standard rate (10 m²/litre)

5. Measure Twice, Buy Once

Double-check your measurements. A 1m error on a wall length can mean 6 m² difference — that's nearly a litre of paint per coat.

Let Us Do the Maths for You

Don't want to calculate? Send us your room measurements on WhatsApp, and we'll provide you with the exact details you need — including quantity, product, and price.

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