How do I calculate how much paint I need?

Paint needed (litres) = Wall area (m²) × Number of coats / Coverage (m²/L) Step by step: 1. Wall area = 2 × (Length + Width) × Height − door areas − window areas 2. Ceiling area = Length × Width 3. Litres for walls = Wall area × coats / coverage (default 12 m²/L) 4. Litres for ceiling = Ceiling area × coats / coverage (default 10 m²/L) 5. Add a small buffer (5–10%) for touch-ups Example — 4m × 5m room, 2.4m ceiling, 1 door, 2 windows, 2 wall coats: • Gross walls: 2 × (4+5) × 2.4 = 43.2 m² • Less openings: − 1.85 − 2.4 = 38.95 m² • Wall paint: 38.95 × 2 / 12 = 6.49 L • Ceiling: 20 m² × 1 / 10 = 2.0 L • Total: 8.49 L → buy 1 × 5L + 1 × 2.5L + 1 × 1L

How many coats of paint do I need?

Number of coats depends on the situation: • 1 coat: Touch-up, same or very similar colour, surface in good condition • 2 coats: Standard for most repaints — recommended default • 3 coats: Significant colour change (dark to light, or light to dark), new plaster, bare wood, heavily stained surface • Primer + 2 coats: Raw plasterboard, new render, bare metal, previously unpainted wood Always allow full drying time between coats — typically 2–4 hours for emulsion, 6–8 hours for gloss/satinwood. Applying a second coat too soon causes the paint to pull and roll, ruining the finish.

What does coverage mean on a paint tin?

Coverage (or spreading rate) is printed on every tin as 'X m² per litre' or 'X sq ft per gallon'. It tells you how far one litre will spread in one coat. Typical coverages: • Standard emulsion (walls): 10–12 m²/L • Ceiling paint: 10 m²/L • Satinwood / eggshell: 12–14 m²/L • Gloss (wood & metal): 12–14 m²/L • Primer: 8–10 m²/L • Masonry paint: 4–6 m²/L (porous surfaces absorb more) • US standard: ~400 sq ft/gallon = ~10 m²/L Note: coverage figures are for smooth, non-porous surfaces in ideal conditions. Textured, porous, or very dark walls will require more paint than the tin states. Always add at least 10% to your calculated quantity.

How do I calculate paint for a room with high ceilings?

The formula is the same — just enter the actual ceiling height. High ceilings have a big impact on paint quantity because wall area is directly proportional to height. Example comparison — same 4m × 5m room: • Standard 2.4m ceiling: wall area = 38.95 m² → 6.5 L (2 coats) • High 3.0m ceiling: wall area = 52.15 m² → 8.7 L (2 coats) • Loft 4.0m ceiling: wall area = 69.55 m² → 11.6 L (2 coats) For rooms with vaulted or sloped ceilings, calculate the ceiling area separately using the slope formula (similar to roof area calculation) and add it to the flat wall area.

Should I use a primer before painting?

Primer is needed in specific situations: • New plaster: Always prime. New plaster is highly porous and will soak up emulsion unevenly, leaving a patchy finish. Use diluted PVA (4:1) or a dedicated mist coat as a primer. • Previously bare/unpainted surfaces: Prime before topcoat • Strong existing colour: Prime to reduce the number of topcoats needed • Going from dark to light: Primer dramatically reduces the coats of topcoat required • Oil-based over water-based: Use a stain-blocking primer between incompatible systems • Water stains or marks: Use stain-blocking primer (Zinsser BIN or similar) For standard repaints of walls in good condition with a similar colour, primer is not usually necessary.

What size tins should I buy?

Buy the fewest and largest tins that meet your requirement — large tins are more economical and reduce the number of batch mixes: • Metric: 10L > 5L > 2.5L > 1L (avoid 750ml and sample pots for anything over 1 m²) • US: 5 gallon > 1 gallon > 1 quart Example — need 8.5L: • Option A: 1×5L + 1×2.5L + 1×1L = 8.5L exact (best) • Option B: 2×5L = 10L (1.5L leftover — keep for touch-ups) • Option C: 9×1L — never do this, costs much more Always buy all tins from the same batch number to guarantee colour consistency. Different production batches can have subtle colour variation.

Paint Calculator — How Much Paint Do You Need?

The Paint Calculator works out exactly how many litres of paint to buy for any room. Enter your room length, width, and ceiling height in metres or feet, subtract doors and windows, choose your number of wall and ceiling coats, and the calculator instantly outputs paint needed in litres, a smart tin size recommendation..

ROOM DETAILS

LENGTH (m)

WIDTH (m)

HEIGHT (m)

DOORS (subtract from walls)

WINDOWS (subtract from walls)

WALL COATS

CEILING COATS

Include ceiling paint

Add primer coat (1 coat, 8 m²/L)

⚙ Adjust coverage rates (m²/L)

Walls

Ceiling

Primer

Check your paint tin label for exact coverage. Defaults: walls 12 m²/L, ceiling 10, primer 8.

WALL COLOUR

CEILING COLOUR

PRICE PER LITRE (optional)

RESULTS

TOTAL PAINT NEEDED

8.49 L

TIN RECOMMENDATION

WALLS (6.49 L)

1 × 5 L + 1 × 1 L + 1 × 1 L

CEILING (2.00 L)

2 × 1 L

ROOM PREVIEW

PAINT SUMMARY

Wall area (net)38.9 m²

Ceiling area20.0 m²

Perimeter18.0 m (skirting/trim guide)

Wall paint (2 coats)6.49 L

Ceiling paint (1 coat)2.00 L

TOTAL PAINT8.49 L

COVERAGE REFERENCE

Standard emulsion (walls)10–12 m²/L

Ceiling paint10 m²/L

Gloss / satinwood (trim)12–14 m²/L

Primer8–10 m²/L

Masonry paint (exterior)4–6 m²/L

US standard (400 sqft/gal)~10 m²/L

NUMBER OF COATS GUIDE

1 coat

Touch-up, same colour, good condition

2 coats

Standard — recommended for most rooms

3 coats

Dark over light, light over dark, new plaster

Created with❤️byeaglecalculator.com

HOW TO USE

1
Enter your room dimensions — length, width, and ceiling height. For irregular rooms, measure the largest rectangle that contains the room. Then enter the number of doors and windows you want to subtract from the wall area. A standard door is approximately 1.85 m² and a standard window 1.2 m² — these are deducted automatically from the gross wall area.
2
Set the number of coats for walls and ceiling. Two coats is the standard for most repaints. Use three coats when dramatically changing colour (dark over light, or light over dark) or when painting new plaster. Toggle the ceiling on or off, and toggle the primer option if your walls need a primer coat first.
3
The coverage rates default to industry standard values (walls 12 m²/L, ceiling 10 m²/L, primer 8 m²/L). Expand the 'Adjust coverage rates' section to enter the exact coverage from your chosen paint tin label — this gives you a more accurate result, especially for specialist paints with lower coverage.
4
Use the colour pickers to select your wall and ceiling colours — the isometric room preview updates live to show you how the colours look together in context. This also makes the snapshot feature more useful as a colour planning tool.
5
Read the results: total litres needed, a smart tin recommendation showing the most efficient combination of available tin sizes (10L, 5L, 2.5L, 1L for metric; 5gal, 1gal, 1qt for US), and a total material cost if you entered a price per litre. The perimeter measurement in the summary helps you estimate skirting board and trim paint quantities separately.

WORKED EXAMPLE

How much paint for a 4m × 5m bedroom, 2.4m ceiling, 1 door, 2 windows, 2 coats walls, 1 coat ceiling? Step 1: Gross wall area 2 × (4 + 5) × 2.4 = 2 × 9 × 2.4 = 43.2 m² Step 2: Subtract openings 1 door: 0.9 × 2.05 = 1.845 m² 2 windows: 2 × 1.2 = 2.4 m² Net wall area: 43.2 − 1.845 − 2.4 = 38.955 m² Step 3: Wall paint (2 coats, 12 m²/L coverage) 38.955 × 2 / 12 = 6.49 L Step 4: Ceiling paint (1 coat, 10 m²/L coverage) 4 × 5 = 20 m² 20 × 1 / 10 = 2.0 L Step 5: Total paint needed 6.49 + 2.00 = 8.49 L Step 6: Tin recommendation (metric) Walls (6.49L): 1 × 5L + 1 × 2.5L (total 7.5L — 1L spare for touch-ups) Ceiling (2.0L): 1 × 2.5L (0.5L spare) Step 7: Cost at $7/litre 8.49 × $7 = $59.43 in paint

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Last updated: April 29, 2026 · Formula verified by EagleCalculator team · Eagle-eyed accuracy for every calculation.