Paint Calculator - Litres, Coats, Cans and Cost
Work out exactly how much paint you need for any room, wall, ceiling, door or exterior - with coats, primer, coverage per litre, wastage and cost included. Six painting modes with real-world coverage rates.
Advanced options
Total Paint Needed
Full Material Breakdown
| Item | Quantity | Notes |
|---|
Cans to Buy (split by can size)
| Can size | Cans needed | Total litres |
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Use Paint Calculator for Walls, Ceilings, Trim and Exteriors
Pick your surface, enter the area or dimensions, choose your paint type and number of coats, and the calculator returns the exact litres of paint, cans to buy, primer required, and total cost.
Paint Coverage Reference by Type
Coverage per litre varies significantly by paint type and surface. These are the industry-standard ranges every major manufacturer uses.
| Paint type | Coverage per litre | Coats | Best for |
|---|---|---|---|
| Matt emulsion | 12 - 14 m²/L | 2 | Interior walls, ceilings |
| Silk / satin emulsion | 12 - 14 m²/L | 2 | Interior walls, wet areas |
| Eggshell | 12 - 14 m²/L | 2 | Interior woodwork, kitchens |
| Gloss | 14 - 16 m²/L | 2 | Trim, doors, radiators |
| Masonry paint | 6 - 8 m²/L | 2 | Exterior walls, render |
| Primer / undercoat | 10 - 12 m²/L | 1 | Bare surfaces, colour change |
| Spray paint (thinned) | 6 - 10 m²/L | 2 - 3 | Doors, cabinets, furniture |
| Chalk paint | 10 - 12 m²/L | 2 | Furniture, shabby-chic finish |
How Many Coats of Paint Do You Need?
The correct number of coats depends on the colour change and surface condition. This is the industry-standard guidance.
| Scenario | Coats | Primer? | Notes |
|---|---|---|---|
| Repainting same colour | 2 | No | Standard refresh |
| Light over light | 2 | No | Similar tones |
| Dark over light | 2 - 3 | Yes (tinted) | Tinted primer helps |
| Light over dark | 3 - 4 | Yes | Needs good primer base |
| New plaster / drywall | 2 - 3 | Yes (mist coat) | Mist coat first |
| Bare wood | 2 - 3 | Yes (wood primer) | Knotting solution needed |
| Bare metal | 2 - 3 | Yes (metal primer) | Rust-inhibiting |
| Previously glossed walls | 2 - 3 | Yes (bonding) | Sand first |
| Stained or water damaged | 3 | Yes (stain block) | Stain-blocking primer |
Typical Paint Needed per Room
Quick reference for standard room sizes assuming 2.4 m ceiling and 2 coats.
| Room | Approx wall area | Paint needed (2 coats) | Ceiling (1 coat) |
|---|---|---|---|
| Small bedroom (3 × 3 m) | 29 m² | 5 litres | 2 litres |
| Standard bedroom (4 × 4 m) | 38 m² | 6 litres | 2.5 litres |
| Master bedroom (5 × 4 m) | 43 m² | 7 litres | 3 litres |
| Living room (6 × 4 m) | 48 m² | 7.5 litres | 3.5 litres |
| Open plan (8 × 6 m) | 67 m² | 10 litres | 4.5 litres |
| Kitchen (4 × 3 m) | 34 m² | 5 litres | 2 litres |
| Bathroom (3 × 2 m) | 24 m² | 4 litres | 1.5 litres |
| Hallway (2 × 8 m) | 48 m² | 7.5 litres | 2.5 litres |
| Single door (both sides) | 4 m² | 0.7 litres | — |
| Window frame | 1.5 m² | 0.3 litres | — |
How the Paint Calculator Works
Every result uses the standard method used by painters, decorators and quantity surveyors. Here is the exact process.
- Net area is calculated from your dimensions minus doors and windows, or entered directly.
- Total area to paint = net area x number of coats. Ceiling is added on top if selected.
- Paint volume = total area / coverage per litre, from the standard coverage of your chosen paint type.
- Primer volume = net area / primer coverage (usually 10 m²/L, one coat).
- Wastage is added as a percentage on top so you always have spare paint for touch-ups.
- Cans = volume / can size, rounded up to the nearest whole can so you buy what you need.
- Cost = cans x price per can, live as you type.
Paint Formula and Worked Example
These are the exact formulas used by the calculator. Bookmark this section if you want to verify the numbers yourself.
- Net area = length x height - openings
- Total paint area = net area x coats + (ceiling area x 1)
- Litres needed = total paint area / coverage per litre
- Litres with waste = litres needed x (1 + waste%)
- Cans = ceil(litres with waste / can size)
- Primer = net area / 10 m²/L
- Cost = cans x price
Worked example: A 5 m x 2.7 m wall, one wall only, with 3 m² of window deducted, painted with 2 coats of 14 m²/L premium emulsion, 5 L cans, 10% waste. Net area = (5 x 2.7) - 3 = 10.5 m². Total paint area = 10.5 x 2 = 21 m². Litres = 21 / 14 = 1.5 L. With 10% waste = 1.65 L. Cans = ceil(1.65 / 5) = 1 can. If the wall needs 4 walls (20 m² net) with 2 coats = 40 m² total, litres = 40 / 14 = 2.86 L, with waste = 3.14 L, cans = 1 x 5 L. Same can.
Frequently Asked Questions About Paint Calculation
How much paint do I need for a room?
Measure the total wall area (perimeter x height), subtract doors and windows, then multiply by the number of coats. Divide by the paint's coverage per litre (usually 12 - 14 m²/L for interior emulsion). For a standard bedroom with 40 m² of wall and 2 coats, you need about 6 litres of paint. The calculator handles all of this automatically.
How many coats of paint do I really need?
Two coats is standard for repainting an existing surface. For new plaster or drywall, apply a mist coat (thinned primer) first then 2 finish coats. For a dramatic colour change, use a tinted primer plus 2 - 3 finish coats. For light over dark, you may need 3 - 4 coats total including primer. Never rely on a single coat for a durable finish.
How many square metres does 1 litre of paint cover?
Standard emulsion covers 12 - 14 m² per litre on smooth interior walls. Masonry paint covers only 6 - 8 m² per litre because textured exterior surfaces absorb more. Gloss covers 14 - 16 m²/L on smooth trim. Always check the specific paint's datasheet - cheap paints cover less, premium paints more.
Should I count the ceiling in paint calculations?
Only if you plan to paint it. Ceiling paint uses the same area formula (length x width) but usually a flat matt finish and only 1 - 2 coats. Many people repaint ceilings only every 3 - 5 years. The calculator has a "Walls + ceiling" option if you want to include it.
How do I paint a room with multiple colours?
Split the room into zones by wall. Calculate paint for each zone separately using only the walls that get that colour. Add 10% waste to each colour for touch-ups. The calculator's "Feature Wall" mode is designed for this - just calculate the accent wall separately from the main walls.
How much wastage should I allow for paint?
10% is standard for interior painting. Increase to 15% for spray painting (overspray) and 20% for textured or porous surfaces (first coat absorbs more). Always keep leftover paint for future touch-ups - it will dry out if not sealed tightly.
Do I need primer before painting?
Yes in these cases: new plaster or drywall (mist coat), bare wood (knotting + wood primer), bare metal (rust-inhibiting primer), colour change from dark to light (tinted primer), stained surfaces (stain-blocking primer), previously painted with gloss (bonding primer). Skip primer only when repainting a similar colour over a sound existing finish.
What is a mist coat and do I need one?
A mist coat is paint thinned with 10 - 20% water, applied to new plaster or bare drywall before the finish coats. It soaks into the porous surface and seals it, preventing the finish coats from being absorbed unevenly. Without a mist coat, your topcoats will dry patchy and use much more paint. Always apply a mist coat on new plaster.
How long does paint take to dry between coats?
Water-based emulsion: 2 - 4 hours between coats, 24 hours before heavy use. Oil-based gloss: 16 - 24 hours between coats. Spray paint: 1 - 2 hours between light coats. Always follow the specific paint's datasheet - humidity and temperature affect drying time significantly. Do not rush coats or the finish will fail.
Can I use the same paint on walls and ceiling?
Yes, but ceilings look best with flat matt emulsion because it hides imperfections and reflects less light. Walls often look better with silk or satin because they are washable. Using one product for both is fine for a budget job - just don't use gloss on a ceiling.
How much paint for doors and trim?
Each standard interior door (2 m x 0.8 m, both sides) needs about 0.5 - 0.7 litres of gloss for 2 coats. Window frames take about 0.3 litres each. Skirting board needs about 0.5 litres per 10 m of length. Use the "Trim & Doors" mode in the calculator for precise figures.
What is the difference between emulsion, eggshell and gloss?
Emulsion is water-based, dries matt or silk, best for walls. Eggshell has a low sheen - durable and washable, good for kitchens and woodwork. Gloss is highly reflective and very hard-wearing, best for trim, doors and radiators. Satin sits between eggshell and gloss. Choose based on the finish you want and how much wear the surface takes.
Why does paint quantity differ between brands?
Coverage depends on titanium dioxide content (the main pigment), the binder quality, and the paint's viscosity. Premium paints have more TiO₂ and cover in fewer coats. Cheap paints often need 3 coats where a premium product needs 2. Check the manufacturer's stated coverage on the tin - the calculator lets you adjust it.
How do I store leftover paint?
Seal the lid tightly and store upright in a cool, dry place away from direct sunlight. Write the date and room on the tin so you know what it is later. Water-based paint lasts 2 - 3 years if stored correctly; oil-based lasts 5 - 10 years. If the paint has separated, stir thoroughly before use.
References & Standards
- BS 6150 - Code of practice for painting of buildings
- BS EN 13300 - Paints and varnishes: Classification of water-borne coating materials
- ISO 2812 - Paints and varnishes: Determination of resistance to liquids
- ASTM D523 - Standard Test Method for Specular Gloss
- ASTM D2805 - Standard Test Method for Hiding Power of Paints
- AS 2311 - Painting of buildings (Australia)
- NIS 550 - Nigerian Industrial Standard Building Code
- NBC 2016 - National Building Code of India, Part 4