Surface Dimensions
Paint Settings
Paint Pricing (Optional)
Enter your dimensions
Input your surface dimensions, number of coats, and paint coverage to calculate exactly how much paint you need to buy.
What is a paint calculator?
A paint calculator is a practical tool designed to help you estimate the exact volume of paint required for decorating projects. Whether you are painting a single accent wall, an entire room, or a ceiling, this tool prevents you from buying too much paint (wasting money) or too little (causing frustrating mid-project store runs).
By factoring in the surface area, the number of coats, the specific coverage rate of your chosen paint brand, and a standard waste allowance, the calculator provides a highly accurate estimate of the litres and tins you need to purchase.
How to use this calculator
- 1
Select Mode: Choose Wall (for specific surfaces), Room (for 4 walls), or Ceiling.
- 2
Enter Dimensions: Measure your surfaces in metres. For rooms, enter the number of doors and windows to subtract their area.
- 3
Check Coverage: Look at your paint tin. Standard emulsion covers about 10-12m² per litre, but this varies by brand and finish.
- 4
Add Primer: If painting bare plaster or making a drastic colour change, toggle Primer to 'Yes'.
Important Painting Factors
How Quantity is Calculated
We calculate the total gross area, subtract any openings (doors/windows), multiply by the number of coats, add a waste percentage, and divide by the paint's coverage rate (m²/L) to find the total litres needed.
Why Coats Matter
Almost all painting projects require at least two coats for a solid, even finish. Painting over dark colours with light colours may require three coats. Each additional coat doubles or triples your required paint volume.
Paint Coverage Rates
Coverage dictates how far the paint spreads. Standard matte emulsion covers ~10m²/L. High-quality trade paints might cover 14m²/L. Textured surfaces (like roughcast) absorb more paint, dropping coverage to 6-8m²/L.
When to use primer
Primer is a preparatory coating put on materials before painting. It ensures better adhesion of paint to the surface, increases paint durability, and provides additional protection for the material being painted.
You should use primer when: painting bare wood or new drywall/plaster (which is highly porous and will soak up expensive topcoat paint); painting over dark colours with light colours; painting over glossy finishes; or painting surfaces with stains or water damage. Primer is usually applied as a single coat.
Common calculation mistakes
Forgetting to multiply the area by the number of coats required.
Not subtracting large windows and doors, leading to over-purchasing.
Assuming all paints have the same coverage rate (always check the tin).
Ignoring the texture of the wall (rough surfaces need up to 20% more paint).
Not buying enough paint from the same batch, resulting in slight colour variations if you have to buy more later.
Example Calculations
Room Paint Calculation
Painting a 4m × 5m room with 2.4m ceilings. It has 1 door (1.6m²) and 1 window (1.2m²). 2 coats needed, coverage 10m²/L.
- • Gross Area = 2 × (4 + 5) × 2.4 = 43.2m²
- • Openings = 1.6 + 1.2 = 2.8m²
- • Paintable Area = 43.2 - 2.8 = 40.4m²
- • 2 Coats Area = 40.4 × 2 = 80.8m²
- • Plus 10% Waste = 88.88m²
- • Paint Needed = 88.88 / 10 = 8.89 Litres
Ceiling Calculation
Painting the ceiling of the same 4m × 5m room. 2 coats needed, coverage 12m²/L.
- • Ceiling Area = 4 × 5 = 20m²
- • 2 Coats Area = 20 × 2 = 40m²
- • Plus 10% Waste = 44m²
- • Paint Needed = 44 / 12 = 3.67 Litres
- • You would buy one 5L tin of ceiling paint.
Frequently Asked Questions
Important Disclaimer
Related Calculators
Calculation method, worked example and reference
What this calculator does and formula: Paintable area is the sum of surface areas minus openings. Required paint = area × coats ÷ stated coverage, then waste is added.
Variables and units: Enter values in the units named by the controls. The calculator converts through its internal base unit or applies the displayed geometric or financial relationship before rounding the presented result.
Verified worked example: A 30 m² wall area, two coats and 10 m²/L coverage requires 6.0 L before waste.
Result interpretation, assumptions and practical limits: Coverage depends on product, substrate, porosity, colour change and application. Follow the coating data sheet and safety instructions.
Professional check: Treat the result as a planning estimate. Where safety, regulated work, contracts or significant money are involved, verify inputs and the result with the governing standard, manufacturer data and an appropriately qualified professional.