Paint Calculator
Calculate exactly how much paint you need. Enter room dimensions, deduct doors and windows, pick the number of coats — get litres and can recommendations instantly.
Calculation Mode
Units
Room Dimensions
Enter the total gross paintable area before deductions.
Doors & Windows
Standard door ≈ 1.9 m² (0.9 m × 2.1 m)
Standard window ≈ 1.4 m² (1.2 m × 1.2 m)
Large built-ins, fireplaces, feature panels, or any other areas not to paint.
Paint Options
Emulsion 10–12, Masonry 6–8
Results
Area Breakdown
Paint Needed
—
litres
Coats
2
applied
Per Coat
—
litres
Waste Buffer
—
litres extra
Recommended Cans
Paint Coverage Reference
| Paint Type | Coverage (m²/L) | Recommended For | Coats Needed |
|---|---|---|---|
| Interior Emulsion / Matt | 10–12 | Walls & ceilings | 2 |
| Silk / Satin Emulsion | 10–11 | Walls in kitchens/bathrooms | 2 |
| Eggshell | 10–12 | Woodwork, walls | 2 |
| Gloss (oil-based) | 12–14 | Woodwork, trim, doors | 2–3 |
| Masonry / Exterior | 6–8 | Exterior walls | 2 |
| Ceiling Paint (thick) | 8–10 | Ceilings only | 1–2 |
| Primer / Undercoat | 10–12 | Bare plaster, new surfaces | 1 |
| High-coverage / One-coat | 8–9 | Quick refresh over similar colour | 1 |
Standard Can Sizes & Coverage
| Can Size | Typical Coverage (1 coat) | Coverage (2 coats) | Best For |
|---|---|---|---|
| 1 L | 10–12 m² | 5–6 m² | Touch-ups, small areas |
| 2.5 L | 25–30 m² | 12–15 m² | Small rooms, feature walls |
| 5 L | 50–60 m² | 25–30 m² | Average bedroom |
| 10 L | 100–120 m² | 50–60 m² | Large room or multiple rooms |
| 15 L | 150–180 m² | 75–90 m² | Whole house repaint |
Frequently Asked Questions
For a standard room with 4 walls, calculate the total wall area = 2 × (length + width) × height. Subtract the area of doors (~1.9 m² each) and windows (~1.4 m² each). Divide net area by the coverage rate (typically 10–12 m²/L for emulsion). Multiply by the number of coats and add a 10% waste buffer. This calculator automates all of that.
Most interior walls need 2 coats. Going from dark to light — or painting bare plaster — may need 3 coats. New plaster should get a diluted mist coat first, then 2 full coats. Budget one-coat paints cover in a single pass but rarely match the durability of 2-coat finishes.
Coverage rate is how many square metres one litre of paint covers. Interior emulsion: 10–12 m²/L. Silk/satin: 10–11. Gloss: 12–14. Masonry: 6–8. Always check the manufacturer label — coverage varies by brand and surface porosity. Rough or porous surfaces (bare plaster, concrete, textured walls) absorb more paint and effectively reduce coverage to the lower end of the range.
A 10% buffer covers spillage, brush/roller absorption, and slight underestimation of area. On textured or rough surfaces, use 15%. Always round up to the nearest can size — running short mid-wall is a problem because colour-matching a second batch is rarely perfect. Leftover paint stores well in a sealed tin for future touch-ups.
Yes, ideally. Ceiling paint is a different product — thicker to prevent drips, and usually a lower coverage rate (8–10 m²/L). Tick "Also paint the ceiling" in this calculator and it adds the ceiling area using the same coverage settings. If you are using different products for walls vs ceiling, calculate them separately using the Custom Area mode.
A standard single interior door is approximately 0.9 m wide × 2.1 m tall = 1.89 m² (rounded to 1.9 m²). A standard window is approximately 1.2 m × 1.2 m = 1.44 m² (rounded to 1.4 m²). Use the "Additional deduction" field for non-standard sizes, large patio doors, skylights, or other openings.
How to Calculate How Much Paint You Need
Buying too little paint means a mid-project run to the store — and potentially an imperfect colour match. Buying too much wastes money. A simple area calculation gets it right every time.
The basic formula for painting four walls in a rectangular room:
- Wall area = 2 × (length + width) × ceiling height
- Deductions = number of doors × 1.9 m² + number of windows × 1.4 m²
- Net area = wall area − deductions
- Litres per coat = net area ÷ coverage rate (m²/L)
- Total litres = litres per coat × coats × (1 + waste buffer %)
Choosing the Right Coverage Rate
The coverage rate printed on a tin is a theoretical maximum — it assumes perfect conditions: smooth, sealed surfaces, consistent application thickness, and no re-brushing. Real-world coverage is typically 5–15% lower. For a first coat on bare plaster, use the low end of the stated range. For a topcoat over an existing similar colour, you can use the high end.
Tips for an Accurate Paint Estimate
- Measure walls individually if the room has alcoves, bay windows, or irregular shapes — use Custom Area mode and add each wall separately.
- If you are painting two colours (e.g. feature wall), split the calculation by colour.
- New plasterboard or bare plaster absorbs a lot of paint on the first coat — budget an extra 20–30% for the mist/sealer coat.
- Textured or Artex ceilings can require twice the paint of a flat surface due to the increased surface area in all the peaks and troughs.
- When buying, choose cans that minimise leftovers: a 5 L + 1 L combination for 5.8 L needed is better than two 5 L cans.