Free Paint Calculator Online
Paint quantity for walls, ceilings and rooms with coverage rate and cost
The Paint Calculator determines how many litres or gallons of paint you need to cover walls and ceilings in a room, accounting for doors, windows, number of coats, and paint coverage rate. Interior decorators, DIY renovators, and painting contractors use it to avoid buying too little (requiring a mid-job store run) or too much (wasting expensive paint).
Frequently Asked Questions
About the Paint Calculator
Paint coverage varies significantly between product types: economy emulsions often cover 10–11 m² per litre, premium matt finishes 12–14 m², and specialist paints like wood primers or masonry paint have their own stated coverage rates on the tin. Using the wrong coverage figure is the most common reason paint estimates miss by 20–30%.
The calculator deducts door and window areas before computing paint volume — a step often skipped in quick estimates. For highly porous surfaces like bare plaster or new plasterboard, the first coat acts as a seal and covers significantly less area than the stated rate; the calculator includes a porosity adjustment for this case.
Ceiling paint is almost always white and uses a different product from wall paint, so the calculator separates wall and ceiling quantities. For multi-room projects, add each room separately and sum the totals to get one shopping list that covers the entire job.
Formula Used
Paint Needed = Wall Area / Coverage Rate per Gallon × Number of Coats
When Should You Use This?
The Paint Calculator is ideally suited for contractors, builders, architects, and DIY enthusiasts who need to perform quick, accurate calculations related to general calculations. Use this tool when you need to verify figures, compare different scenarios, or get a precise answer without manual computation errors.
What Does The Result Mean?
The calculated output provides an instant, accurate resolution to your input parameters. You can use these results directly for your planning, assignments, or professional tasks, knowing they are based on standardized formulas.
Example Calculation
Painting a bedroom: 4 m × 3.5 m room, 2.4 m ceiling height
📥 Inputs
- Room: 4 m × 3.5 m, height 2.4 m
- Two doors: each 0.9 m × 2.1 m
- One window: 1.2 m × 1.0 m
- Two coats of paint, coverage: 12 m²/litre
🔢 Calculation Steps
- 1Total wall perimeter: 2 × (4 + 3.5) = 15 m
- 2Gross wall area: 15 × 2.4 = 36 m²
- 3Subtract doors: 2 × (0.9 × 2.1) = 3.78 m²
- 4Subtract window: 1 × (1.2 × 1.0) = 1.20 m²
- 5Net wall area: 36 − 3.78 − 1.20 = 31.02 m²
- 6Two coats: 31.02 × 2 = 62.04 m²
- 7Paint needed: 62.04 ÷ 12 = 5.17 litres → buy 6 litres (2 × 2.5 L tins)
Limitations of this Calculator
- Results are based purely on the mathematical relationship of the inputs provided.
- Does not account for edge cases or extreme outlier values that fall outside standard formula constraints.
- Calculated outputs should be double-checked against your specific real-world requirements before finalizing important decisions.
How to Use the Paint Calculator
- 1Enter your values into the Paint Calculator input fields above.
- 2Review the input labels to ensure you are using the correct units.
- 3Click the "Calculate" button to get your instant result.
- 4Use the step-by-step breakdown to understand how the result was calculated.
- 5Export or copy your result to use in reports or share with others.
Tips & Best Practices
- Standard coverage: 1 gallon covers approximately 350-400 sq ft with one coat.
- Double-check your input units before calculating — using the wrong unit is the most common source of errors.
- Bookmark this Paint Calculator for quick access next time you need it.
- Use the share button to send your results to a colleague or save them for later reference.
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