Paint Calculator
Gallons needed for your room
How to Calculate Paint Needed
This calculator estimates paint by calculating the total wall area (perimeter times height), subtracting the area of doors (approximately 21 square feet each) and windows (approximately 15 square feet each), then dividing by the paint coverage rate (typically 350 square feet per gallon). The result is multiplied by the number of coats for the final estimate.
Tips for Painting
Always buy slightly more paint than calculated — about 10% extra for touch-ups and waste. Two coats is standard for most projects, especially when changing colors. Use primer when painting over dark colors or bare surfaces. Store leftover paint properly for future touch-ups.
Practical tips
Use this tool as a quick planning aid, then review the result in context. For home, utility, password, or project estimates, small input changes can make a noticeable difference. When the result affects safety, budget, or security, choose the more careful option and verify the important details before acting.
Common ways people use this tool
This tool is useful for quick planning at home, work, or study. It helps you make a rough estimate before buying materials, checking usage, creating a password, or comparing practical options.
Paint Calculator: practical guide
The Paint Calculator is built for people who want a fast answer without losing context. It keeps the calculation simple, shows the result clearly, and helps you understand what the number means before you use it in a real decision.
This calculator is designed to make a specific everyday calculation faster and clearer. It gives a structured result so you can compare options, check assumptions, or plan the next step with less manual work.
What is the best way to use the Paint Calculator?
Enter the values carefully, review the units, and use the result as a reliable reference point. The Paint Calculator is most useful when you compare scenarios or repeat the calculation with consistent inputs.
Is the Paint Calculator accurate?
The calculator follows standard calculation logic, but accuracy depends on the values you enter and the assumptions behind the formula. For important tools decisions, use it as guidance and verify the result with a trusted source.
How to calculate the amount of paint needed
Accurately estimating paint quantity prevents two common problems: running out mid-project (which risks colour mismatches if the new tin is from a different batch) and over-purchasing expensive paint. The calculation requires the total surface area to be painted, the number of coats, and the paint's coverage rate (typically specified on the tin as square metres per litre).
Paint needed (litres) = Total surface area (m²) × Number of coats ÷ Coverage rate (m²/litre)
Most standard interior emulsion paints cover 10–14 m² per litre per coat. Premium paints often cover more (12–16 m²/L). Textured or porous surfaces absorb more paint and reduce effective coverage by 20–30%.
Calculating wall area step by step
For a rectangular room, calculate each wall's area (width × height), sum them, then subtract doors and windows.
Example — rectangular bedroom:
- Room dimensions: 4.5 m × 3.8 m × 2.7 m (height)
- Two long walls: 2 × (4.5 × 2.7) = 24.3 m²
- Two short walls: 2 × (3.8 × 2.7) = 20.52 m²
- Total wall area: 44.82 m²
- Minus 1 door (2.1 × 0.9 = 1.89 m²) and 2 windows (1.2 × 1.0 = 1.2 m² each): –4.29 m²
- Net paintable area: 40.53 m²
- Two coats at 12 m²/L: 40.53 × 2 ÷ 12 = 6.75 litres needed
- Round up to 7 litres and buy in available tin sizes (most commonly 1L, 4L, 10L)
Coverage rates by paint type
- Interior emulsion (standard): 10–14 m²/L per coat
- Interior emulsion (premium): 12–16 m²/L per coat
- Exterior masonry paint: 6–10 m²/L per coat (rough surfaces absorb more)
- Gloss/satin/eggshell (wood and metal): 14–17 m²/L per coat
- Primer/undercoat: 8–12 m²/L per coat (porous surfaces need more)
- Textured paint: 1–2 m²/kg (significantly lower — applied thickly)
Number of coats guidance
- New walls (fresh plaster): 1 mist coat (thinned paint) + 2 full coats = 3 coats total. New plaster is porous and absorbs the first coat heavily.
- Repainting same colour: Usually 1–2 coats are sufficient if the surface is in good condition
- Changing from dark to light colour: May require 3 coats or an intermediate coat of white/grey primer to prevent the dark colour bleeding through
- Changing from light to dark colour: 2 coats typically sufficient
- Exterior walls: 2 coats minimum; 3 coats for maximum durability in harsh climates
Ceiling paint calculation
For ceiling area: Length × Width of the room. A 4.5 m × 3.8 m room has a ceiling area of 17.1 m². At 2 coats with coverage 12 m²/L: 17.1 × 2 ÷ 12 = 2.85 litres. Buy 3 litres. Ceiling paint is typically specified separately from wall paint as different products are often used (ceiling paint is formulated to resist drips and has a flat finish).
Buying the right tin sizes
Most paint manufacturers sell in standard tin sizes: 1L, 2.5L, 4L or 5L, and 10L. Always round up to the nearest available size. For multiple colours in one room (feature wall different from main walls), calculate each separately and buy accordingly. Having a small amount of leftover paint (100–200ml) is useful for touch-ups later.
Frequently asked questions about paint calculation
Do I need to prime before painting? Primer is needed when: painting over bare wood, metal, or new plaster; painting over a drastically different colour; covering stains or water damage marks; or painting over a very porous surface. Skipping primer on these surfaces leads to poor adhesion, uneven finish, and more top coats needed.
How do I measure an irregularly shaped room? Break the room into rectangular sections, calculate each rectangle's area separately, and sum them. For rooms with alcoves, bays, or columns, add or subtract these areas systematically. The iCalcApp paint calculator handles rectangular rooms; for complex shapes, calculate each section manually and total them.
How much paint do I need for a front door? A standard front door (2.1 m × 0.9 m = 1.89 m²) requires approximately 200–300 ml for two coats of gloss or satin paint. A small 250ml tin is typically sufficient. Don't forget to paint the edges and frame separately if they are a different colour.