Paint Calculator
Example 1
A bedroom 4 m x 5 m, ceiling 2.5 m. One window (1.5 x 1.2 m), one door (0.9 x 2.1 m). Two coats at 11 m²/L.
Solution
Answer
Buy 12 L (3 x 4L cans). Actual paint used ~8.3 L.
Source: ASTM D16: Standard for Paint, Varnish and Related Products
Example 2
Feature wall 6 m x 2.7 m with window (2.4 x 1.5 m) and doorway (0.9 x 2.1 m). Premium satin at 10 m²/L.
Solution
Gross area = 6 × 2.7 = 16.2 m². Openings = 3.6 + 1.89 = 5.49 m². Net = 10.71 m².
Buy 4L can (1L insufficient)
Answer
Need 2.35 L. Buy 4L can, leaving surplus for touch-ups.
Example 3
Home office 3.5 x 4.5 x 2.5 m. Two windows, one door, built-in bookshelf on one wall. Ceiling painted separately. Coverage rate is 11 m²/L.
Solution
Ceiling = 3.5 × 4.5 = 15.75 m². Wall area = 2 × (3.5 + 4.5) × 2.5 = 40 m².
Subtract openings = 26.96 m² paintable wall.
Answer
Walls ~5.4 L (buy 2x4L), ceiling ~3.2 L (buy 1x4L). Two colours needed.
Example 4
A homeowner needs to paint a 4 m × 5 m bedroom with 2.7 m ceilings. There are two windows (1.2 × 1.5 m each) and one door (0.9 × 2.1 m). The paint covers 10 m²/L per coat. How much paint is needed for two coats on the walls plus one coat of primer?
Solution
Window area = 2 × (1.2 × 1.5) = 3.6 m². Door area = 0.9 × 2.1 = 1.89 m².
Net paintable area = 48.6 - 3.6 - 1.89 = 43.11 m².
Two coats: 43.11 × 2 / 10 = 8.62 L. With 10% waste: 9.48 L (buy 2×5L).
Primer: 43.11 / 10 = 4.31 L. With waste: 4.74 L (buy 1×5L).
Answer
Paint needed: 9.5 L for two coats (buy 2 × 5 L tins). Primer: 4.7 L (buy 1 × 5 L). Total cost depends on paint quality tier (economy, standard, or premium).
Published:
Updated:
References
- [1]Sherwin-Williams, Paint Coverage Guide, 2025. https://www.sherwin-williams.com/paint-coverage-guide
- [2]Benjamin Moore, How to Estimate Paint Quantities, 2025. https://www.benjaminmoore.com/paint-estimator-guide
- [3]<a href="https://www.paintingdecoratingassociation.co.uk" target="__blank">Painting and Decorating Association (PDA)</a>, The Painting and Decorating Handbook, 2024.
- [4]US Environmental Protection Agency, Low-VOC Paint Standards, 2025. https://www.epa.gov/indoor-air-quality-iaq/volatile-organic-compounds-impact-indoor-air-quality
Glossary
- Coverage – Wall area that a given volume of paint will cover, usually expressed in m²/L or ft²/gal.
- Primer – A preparatory coating applied before paint to improve adhesion, seal porous surfaces, and block stains.
- Sheen – The gloss level of a paint finish, ranging from flat/matte (no shine) to high-gloss (highly reflective).
- VOC – Volatile organic compounds emitted by paint as it dries; low-VOC paints contain fewer than 50 g/L.
- Waste Factor – The percentage of extra paint added to account for roller tray loss, overspray, and mid-project touch-ups.
- Opacit – The ability of paint to hide the underlying surface colour; higher opacity requires fewer coats.
- Thinner – A solvent used to reduce paint viscosity for spray application or to clean painting tools.
- Mildewcide – An additive that prevents mould and mildew growth on painted surfaces, common in bathroom and exterior paints.
- Spraying – Paint application using a spray gun that atomises paint into a fine mist; faster but uses more paint than rolling.
- Rolling – Paint application using a roller cover on an extension pole; the standard method for walls and ceilings.
How to Use?
- 1
Select calculation mode
Choose from Paint Needed (default), Coverage Rate, or Total Cost mode. The input fields adjust automatically for your selection.
- 2
Enter the total wall area
Measure each wall’s height and width, multiply for area, and add all walls together. Use the unit dropdown to switch between ft², m², and yd².
- 3
Subtract doors and windows
Enter the total area of all doors and windows. A standard door is about 21 ft² and a standard window about 16 ft². Add them together and enter the total.
- 4
Set the number of coats
Most rooms need 2 coats. Use 1 coat for touch-ups or repainting the same colour, and 3 coats for dramatic colour changes.
- 5
Enter the paint coverage rate
Check the paint tin for the manufacturer’s coverage in m²/L. Typical values are 10–12 for smooth walls and 8–10 for textured surfaces.
- 6
Select the surface type
Choose Smooth, Textured, or Rough to adjust coverage for surface porosity and texture. This directly affects the calculated paint volume.
- 7
Set the waste factor
Add 5–10% for waste, roller tray loss, and touch-ups. Use 15–25% if you are spraying instead of rolling.
- 8
Review the results
See the paintable area, effective coverage, exact litres needed, and litres to buy (rounded up). The visual gauge shows your paint volume on a dynamic scale. In Cost mode, the total paint cost is also displayed.
Frequently Asked Questions
Paint coverage is the area a litre of paint can cover when applied at the recommended film thickness, expressed in square metres per litre (m²/L). A paint with 10 m²/L coverage covers 10 square metres per coat per litre. Actual coverage varies by surface type, application method, and painter technique.
Most interior walls need two coats for even, uniform colour. One coat may suffice when repainting the same colour with high-quality paint. Dramatic colour changes (light to dark or dark to light) may need three coats or a primer coat first.
Primer is recommended for new drywall, dark-to-light colour changes, stained surfaces, and porous materials like bare wood or plaster. It seals the surface, improves adhesion, blocks stains, and can reduce the number of paint coats needed. Use the calculator with 1 coat and the primer coverage rate to estimate primer separately.
A waste factor of 5–10% is standard for brush and roller application. This accounts for paint left in the roller tray, on the brush, and minor spillage. For spray application, increase the waste factor to 20–30% to account for overspray losses.
Textured walls have a larger true surface area than smooth walls because the texture adds peaks and valleys that need to be coated. Coverage reduces by about 15% for textured surfaces and 25% for rough surfaces like brick or concrete block. The calculator adjusts for three surface types automatically.
Always measure wall area, not floor area. A 4 m by 5 m room has a 20 m² floor but roughly 45 m² of wall area with a 2.5 m ceiling height. Using floor area instead of wall area would underestimate the paint needed by more than half.
Common container sizes are 1 L, 2.5 L, 4 L, 5 L, and 10 L. The calculator shows both the exact litres needed and the rounded-up buy volume. Use the exact figure to decide which combination of containers gives the best price per litre while covering your needs.
Flat paint has no shine and effectively hides imperfections. Eggshell has a slight sheen and is more washable. Satin has a noticeable sheen and is highly durable. Semi-gloss and gloss are very durable and reflect light. Coverage decreases slightly as sheen increases. Flat covers the most, gloss covers the least.
Yes, spray painting typically uses 15–30% more paint than rolling because of overspray – paint that atomises but never reaches the surface. Increase the waste factor to 20–30% if you are spraying. HVLP sprayers are more efficient than conventional airless sprayers.
Exterior surfaces are typically rougher and more exposed, reducing coverage by 10–20%. Exterior paint also requires more surface preparation and weather-dependent drying time. Use a lower coverage rate (8–9 m²/L) and a higher waste factor (15%) for exterior projects.
Yes, ceilings are typically painted separately with a different paint (usually flat white ceiling paint). Measure the ceiling area (length × width) and calculate it using the paint calculator with the ceiling paint coverage rate. Ceilings usually need only one or two coats.
Paint colour varies slightly between batches due to tolerances in the tinting process. Always buy all the paint you need for a project at the same time and check that the batch numbers match. If you must buy more later, have the store shake the new tin and compare it to your existing paint before committing.
Unopened latex paint lasts 2–5 years when stored in a cool, dry place above freezing. Opened paint can develop a skin, thicken, or grow mould. Store opened tins with the lid tightly sealed, upside down to create an airtight seal, and use within 6 months.
VOCs (volatile organic compounds) are chemicals that evaporate from paint as it dries, contributing to indoor air pollution and the characteristic paint smell. Low-VOC paints contain fewer than 50 g/L, and zero-VOC paints fewer than 5 g/L. They are better for indoor air quality but may dry faster and have slightly different application characteristics.
Latex paint should be applied between 10°C and 30°C. Avoid painting in direct sunlight, which causes the paint to dry too quickly, and in high humidity, which causes runs and sagging. The ideal conditions are a mild, dry day between 18°C and 25°C, with at least 2–4 hours drying time between coats.
Related Calculators
Explore All 2 Construction CalculatorsBrowse by Category
Browse All CategoriesPopular Calculators
Explore All 52 CalculatorsShare: