Paint Calculator
Estimate paint volume for a room or wall project so you can budget materials before heading to the store.
How to use this paint calculator
- Enter room dimensions
Measure and enter the Room length, Room width, and Wall height in meters.
- Set the number of coats
Choose how many paint coats you plan to apply — typically 1–3 depending on coverage and color change.
- Add your coverage assumption
Enter the Coverage per liter from your paint product (usually 8–14 m²/L) or use a conservative average.
- Read the estimated paint needed
The calculator shows the coated wall area and total paint volume required.
- Add a buffer for your project
Round up to the nearest can size and add extra for touch-ups, especially on rough or dark surfaces.
How this paint calculator works
This paint calculator estimates wall area from the room dimensions you enter, multiplies that area by the number of coats, and then divides the result by your paint coverage assumption. It is useful for first-pass budgeting, especially when you want to compare one coat versus two coats or check whether your planned purchase quantity is realistic.
Paint needed = (wall area × number of coats) / coverage per liter If a room has 4 m walls, 3 m walls, and a 2.4 m height, the base paintable wall area is 2 × (4 + 3) × 2.4 = 33.6 m². With 2 coats, the total coated area becomes 67.2 m². At a coverage assumption of 10 m²/L, the paint needed is 67.2 / 10 = 6.72 liters. Rounding up to a 7.5 L or 10 L purchase ensures enough material for touch-ups and absorption on uneven surfaces.
A room with 4 m × 3 m floor and 2.4 m walls has a paintable area of 33.6 m². With 2 coats and 10 m²/L coverage, the paint needed is 6.72 liters. Round up to a 7.5 L or 10 L can and add a small buffer for touch-ups.
If the same 33.6 m² room needed only 1 coat instead of 2, the paint needed would drop to 3.36 liters — about half the amount. Use 1 coat for light refreshes over similar colors; stick to 2 coats for dark-to-light changes or new drywall.
- ✓ The estimate uses a simplified wall-area approach and does not automatically subtract doors, windows, or trim.
- ✓ Coverage per liter is treated as an average and can vary by surface texture, color change, and product type.
- ✓ The output is best used as a shopping estimate rather than an exact supplier order.
- Add a buffer if you are covering dark colors, rough surfaces, or patchy repairs that may absorb more paint.
- For detailed purchase planning, compare the result with the can's stated coverage range instead of assuming every product performs the same way.
- Dulux and Benjamin Moore technical data sheets — manufacturer coverage ranges for interior latex paints
- Painting and Decorating Craftsman's Manual and Textbook — Painting and Decorating Contractors of America (PDCA)
How paint coverage and waste factors work
Paint estimation starts with the paintable wall area: the perimeter of the room (twice the sum of length and width) multiplied by wall height. That gives you the base surface in square meters. Because each coat covers the full area, doubling the number of coats doubles the total coated area and therefore doubles the paint needed. The coverage per liter — how many square meters one liter covers in a single pass — varies by product, surface texture, and color change. Manufacturer ratings assume ideal conditions; rough walls, dark-to-light color changes, and porous surfaces absorb more paint. A waste factor is built in when you round up to the nearest can size and add a small buffer. Running short mid-project means another trip to the store and the risk of a shade mismatch if the new batch differs slightly from the first.
Common paint estimation mistakes
The most frequent mistake is using the manufacturer's best-case coverage number without adjusting for real conditions. A product rated at 12 m²/L may deliver only 9–10 m²/L on textured walls or when covering a dark color with a light one. Another error is forgetting to subtract doors and windows: the calculator uses gross wall area, so a room with large openings needs less paint than the raw result suggests. Measuring in the wrong units — mixing feet and meters, or square feet with liters — also causes ordering errors. Finally, buying exactly the calculated amount with no buffer leaves no room for touch-ups, cutting in around trim, or fixing mistakes. Experienced painters typically add 10–15% to the calculated volume, and for small rooms a single extra liter can make the difference between finishing the job and running out.
Paint calculator FAQs
Does this paint calculator subtract windows and doors?
No. It uses a simple wall-area estimate, so you may want to reduce the result manually if the room has large openings.
Why does a second coat change the result so much?
Because the calculator multiplies the wall area by the number of coats, so every additional coat increases the amount of paint required.
What coverage number should I use?
Use the average coverage printed on your paint product, ideally adjusted conservatively if the wall surface is rough or porous.
Should I buy extra paint?
Usually yes. A small buffer is useful for touch-ups, color matching, and surfaces that absorb more than expected.
Can I use this for a single wall?
Yes, as long as you enter dimensions that reflect the area you actually plan to paint.