Paint Calculator Online — Calculate Litres of Paint Needed

What is a Paint Online?

This free paint calculator online lets you calculate paint coverage litres for any room or surface before you buy — so you order exactly the right amount. Run short mid-job and you face the frustrating — sometimes impossible — task of matching the exact colour from a new production batch. Buy too much and you waste money on tins that sit unused for years. This paint calculator online eliminates the guesswork entirely, giving you a precise litre count based on your actual surface area, surface type, and number of coats — so you arrive at the paint shop with confidence. **Interior vs Exterior Paint** Interior paint and exterior paint are formulated differently and are not interchangeable. Interior paint is designed for washability, low odour, and resistance to scuffs and staining in controlled indoor environments. Exterior paint is engineered to survive UV radiation, rain, humidity swings, and thermal expansion — it contains fungicides, mildewcides, and more flexible binders to resist cracking and peeling. Using interior paint outdoors causes rapid deterioration, while exterior paint indoors is unnecessarily costly and may off-gas for longer. This interior paint calculator and exterior paint calculator both give accurate results — the key difference is in the paint you purchase, not in the area or coverage calculation itself. **What Affects Paint Coverage** Paint coverage varies significantly with surface condition and material, making surface type the most important variable in the calculation. Smooth plaster and drywall absorb the least paint, covering 10–12 m² per litre per coat. Rough or textured walls have a larger effective surface area and typically yield only 6–8 m² per litre. New bare plaster is the most absorbent substrate — without a primer coat it can consume 30–40% more paint than a previously painted wall, covering just 5–7 m² per litre. Ceilings are generally smooth and cover at 10–12 m² per litre. Non-porous wood and metal surfaces, with suitable primer, typically allow 12–14 m² per litre. The surface type dropdown in this paint coverage calculator sets the correct rate automatically — no manual lookup required. **Paint Coverage by Surface Type** Smooth Plaster / Drywall: 10–12 m² per litre | Rough / Textured Walls: 6–8 m² per litre | New Bare Plaster: 5–7 m² per litre (highly absorbent — always apply primer first) | Ceiling: 10–12 m² per litre | Wood or Metal: 12–14 m² per litre. **How to Measure Wall Area for This Paint Calculator for Walls** Measure each wall's length and height in metres and multiply them. Add all walls you plan to paint. Subtract the area of any doors and windows you are not painting: a standard interior door is approximately 1.8m × 2.1m = 3.78 m². A standard window is approximately 1.2m × 1.2m = 1.44 m². For example, a 4m × 5m room with 2.7m ceilings, one door, and two windows has a total wall area of: (4+5+4+5) × 2.7 − 3.78 − (2 × 1.44) = 48.6 − 6.66 = 41.94 m². Entering this figure into the calculator — rather than the raw perimeter times height — gives you an accurate answer and saves you from over-buying.

How to Use This Calculator

Using this paint coverage calculator is straightforward. Enter the total surface area to be painted in square metres — use the measurement guide above to calculate your net area after subtracting doors and windows for the most accurate result. Next, select your surface type from the dropdown: Smooth Plaster / Drywall, Rough / Textured Walls, New Bare Plaster, Ceiling, or Wood or Metal. The calculator automatically applies the correct coverage rate for that material — there is no need to look up figures from a paint tin or manufacturer's website. Finally, select the number of coats: most walls being repainted over a similar existing colour need 2 coats; drastic colour changes or very dark topcoats over light backgrounds typically require 3. Click Calculate to instantly see how many litres of paint you need, the recommended purchase quantity with a 10% safety buffer always included, the number of standard 4-litre tins and 20-litre drums to buy, and the coverage rate applied. Wondering "how many litres of paint do I need for my bedroom?" — enter your wall area, select Smooth Plaster, choose 2 coats, and you have your answer in seconds. Whether you are using this as an interior paint calculator for a living room makeover or as an exterior paint calculator for a full house facade, the output tells you exactly what to order. To calculate paint coverage litres for multiple rooms with different surfaces, run a separate calculation for each surface type and add the results together.

💡 Pro Tips

• ✓Subtract doors and windows from your total area before entering it — a standard door (1.8m × 2.1m = 3.78m²) and window (1.2m × 1.2m = 1.44m²) add up quickly and overstating your area leads to unnecessary overpurchasing.
• ✓Always buy paint from the same batch number, printed on the tin label — colour can vary subtly between different production batches, and mismatched batches are often visible on a finished wall when viewed in raking or natural light.
• ✓Apply a primer on new bare plaster, raw wood, or any highly porous surface before your topcoat — primer seals the surface and can cut topcoat consumption by 30–40%, saving more than the cost of the primer itself.
• ✓Darker colours, deep reds, oranges, and saturated yellows often require 3 or even 4 coats for full opaque coverage — calculate using your actual coat count, not the standard 2, to avoid running short on the final coat.
• ✓Store leftover paint in an airtight container with the lid pressed down firmly — properly sealed paint lasts 2–5 years for touch-ups, and matching a slightly aged tin is far easier than mixing a new colour to match an old wall.
• ✓For exterior walls, add an extra 15% buffer instead of 10% — outdoor masonry surfaces are more variable in porosity, wind and temperature affect how evenly paint applies, and getting more delivered at once saves on repeat visits.
• ✓Choose your paint finish before calculating — flat and matte finishes hide imperfections but are harder to clean; eggshell and satin are washable and work well in kitchens and bathrooms; gloss is the most durable but amplifies every surface irregularity. Different finishes in the same product range may have slightly different coverage rates.
• ✓If your project spans multiple surface types — smooth walls plus a new plaster patch plus timber skirting boards — calculate each surface type separately using the surface dropdown and add the results. A single blended calculation will underestimate paint for the more absorbent surfaces.

Who Uses This Calculator?

This paint calculator online is the essential first step for anyone buying paint. Homeowners repainting a bedroom, living room, kitchen, or bathroom use it to calculate exactly how many tins to buy before their trip to the paint shop — avoiding both the mid-project shortage and the waste of excessive stock. Homeowners painting exterior facades use it as an exterior paint calculator to estimate large surface areas where ordering errors are costly. Contractors and professional painters use it to prepare accurate material cost estimates for client quotes, ensuring profit margins are protected and clients are charged correctly. Interior designers and architects specify paint quantities in renovation project documentation and material schedules. Property developers budgeting finishing costs across multiple apartments or houses use it to prepare bulk procurement orders. Landlords and property managers calculating quantities for multiple rooms or entire residential units use it to prepare supplier orders efficiently. DIY first-timers planning their first painting project avoid the two most common mistakes — running out of paint mid-wall and buying far too much — with a single calculation. Anyone who has ever stood in a paint shop wondering "how many litres of paint do I need?" will find a precise, surface-specific answer here.

Frequently Asked Questions