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Walls + Ceiling
🎨 Paint Calculator
Enter room length, width, and ceiling height to instantly calculate paint litres for walls and ceiling - with automatic door and window deductions. Set your paint coverage rate, number of coats, and tin size to see exactly how many tins to buy and the total cost. Add multiple rooms for a whole-house estimate.
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Total Paint Needed
Room-by-Room Calculator
Add each room individually for a whole-house estimate.
Paint Calculation Guide
Basic Formula
Net Paintable Area = Total Wall Area
- Door Area (2.0 × 0.9 = 1.8 m² each)
- Window Area (1.2 × 1.0 = 1.2 m² each)
Paint Needed (L) = Net Area × No. of Coats
/ Coverage per Litre
Tins to Buy = Ceil(Paint Needed / Tin Size)
Example: 4m × 3.5m room, 2.8m ceiling, 1 door, 2 windows
Wall area = (4+3.5+4+3.5) × 2.8 = 42 m²
Ceiling = 4 × 3.5 = 14 m²
Deduct = 1×1.8 + 2×1.2 = 4.2 m²
Net area = (42 + 14) − 4.2 = 51.8 m²
2 coats, 14 m²/L:
Paint = 51.8 × 2 / 14 = 7.4 L
Tins = 2 × 4L tins
Standard Coverage Rates (Litres per m²)
Economy emulsion: 12–13 m²/L
Standard emulsion: 14–16 m²/L
Premium emulsion: 16–18 m²/L
Exterior emulsion: 10–12 m²/L
Texture paint: 8–10 m²/L
Masonry paint: 7–10 m²/L
Primer / undercoat: 10–12 m²/L
Gloss / enamel (metal): 14–16 m²/L
Wood paint: 12–14 m²/L
Note: Coverage reduces on rough/porous surfaces.
Always buy 10% extra for wastage and touch-ups.
When to Use Primer?
New plaster / bare walls: Always use primer
Changing from dark to light: Use white primer
Previously painted (good): Usually skip primer
Stained/water-marked walls: Stain-block primer
Old chalky/flaking paint: Sand + seal first
Primer typically reduces final coats needed
from 3 to 2, saving overall paint cost.
Frequently Asked Questions
Wall area = room perimeter × ceiling height. Perimeter = (length + width) × 2. Example: 5m × 4m room, 2.7m ceiling. Perimeter = 18m. Wall area = 18 × 2.7 = 48.6 m². Subtract doors (~1.8 m² each) and windows (~1.2 m² each). Add ceiling area (length × width) if painting. Divide net area by paint coverage per litre. Multiply by number of coats. Add 10% wastage buffer. Always round up to the nearest tin. This calculator does all of this automatically from your room dimensions.
Coverage varies by paint type: standard interior emulsion 12–15 m²/L, premium interior 14–18 m²/L, economy 10–12 m²/L, exterior masonry 8–12 m²/L, primer 10–12 m²/L. Always check the specific coverage rate printed on the tin or manufacturer data sheet - rates vary between brands. Surface texture also matters: smooth plasterboard has the highest coverage; rough or porous surfaces absorb significantly more and give lower effective coverage.
Repainting same or similar colour: 1–2 coats. Changing from dark to light: 2–3 coats or use a tinted white primer first to reduce coats. New plaster or bare drywall: 1 coat diluted primer + 2 finish coats minimum. Deep/rich colours (dark tones, strong saturation): 2–3 coats for full coverage. Using a quality primer coat before finish paint reduces the number of finish coats needed, improves adhesion, and extends the life of the paint job.
Yes, if painting new surfaces, bare plaster, new drywall, or making a dramatic colour change. Primer is calculated separately: typically 10–12 m²/L for one coat. Primer seals porous surfaces so finish paint applies evenly and goes further. For new plaster: apply 1 diluted coat (10–20% water addition) as a mist coat, then 2 finish coats. For repainting existing painted walls in good condition, primer is usually not needed - proper preparation (cleaning, light sanding) is sufficient.
Interior emulsion: water-based, low VOC, designed for indoor conditions. Not weather-resistant - will crack, fade, and peel outdoors within months. Exterior/masonry paint: contains fungicide (prevents mould and mildew), UV stabilisers (prevents fading and chalking), and flexible binders that handle thermal expansion. Lower coverage rate (8–12 m²/L) than interior due to heavier pigment load. Never use interior paint outdoors. Apply exterior paint in dry conditions above 10°C.
For small jobs under 2L: 1L or 2.5L tins. Single room: 4L or 5L tins offer good economy. Multiple rooms: 10L tins give the best price per litre. Whole house: 15L or 20L where available. Avoid buying multiple small tins when one large tin will do - price per litre drops significantly with size. Ensure you buy enough to complete each surface from one batch - different batches of the same colour can have slight variations visible on the finished surface.
Rough textured surfaces (sand render, pebble dash, raw brickwork) use significantly more paint than smooth surfaces - typically 40–70% more. For rough render: use 6–9 m²/L instead of 12–15 m²/L. For raw brickwork: 5–8 m²/L. The surface has more total area (more peaks and valleys) and absorbs more paint. In this calculator, enter the lower coverage rate in the 'Coverage per litre' field to adjust for your surface type. New rough surfaces will also need 2–3 coats to fully seal and cover.
Buy precisely - calculate accurately and add only 10% buffer, not the 20–25% many stores suggest. Mix all tins of the same colour together in a large bucket before starting (called 'boxing') to prevent subtle batch-to-batch colour differences. Apply in an N or W pattern with a roller for even coverage and minimal overlapping. Store leftover paint correctly: seal tins tightly, store upside down for the first day (forms an airtight seal), keep in a cool dry place. Well-sealed paint lasts 2–3 years.
Paint Calculator - How to Calculate Paint for Any Room or House
Buying too much paint wastes money. Buying too little means a mid-project trip back to the hardware store, and a risk that the new batch is a slightly different shade. Accurate paint estimation takes three minutes with this calculator - far less time than guessing and dealing with the consequences.
Step-by-step example: Living room 5m × 4m, 2.7m ceiling height, 2 doors (1.8 m² each), 2 windows (1.2 m² each), 2 coats of standard interior emulsion (12 m²/L coverage). Wall area = (5+4)×2 × 2.7 = 48.6 m². Deduct 4 openings: 48.6 − 6.0 = 42.6 m². Paint needed = 42.6 ÷ 12 × 2 = 7.1 litres. Buy two 4L tins or one 8L tin.
Paint Coverage Rates - What to Expect by Paint Type
Interior Paint Coverage
- Economy/budget emulsion: 10–12 m²/L. Lower pigment load, often thinner consistency.
- Standard interior emulsion: 12–15 m²/L. The most common type for walls and ceilings.
- Premium interior paint: 14–18 m²/L. Higher pigment density, better one-coat coverage.
- Flat/matte finish: Hides imperfections well; typically 12–14 m²/L.
- Satin/semi-gloss: More durable, washable; slightly lower coverage 10–13 m²/L.
Exterior & Specialty Coverage
- Exterior/masonry paint: 8–12 m²/L. Higher pigment for opacity and UV resistance.
- Primer/undercoat: 10–12 m²/L. Applied before finish coats on new surfaces.
- Textured/rendered surfaces: 6–9 m²/L. Porous surface absorbs significantly more.
- Gloss paint (doors, trim): 12–14 m²/L for brushed application.
- Always check the specific coverage stated on the manufacturer's tin - it varies by product.
How Many Coats Do You Need?
- Repainting same or similar colour (good existing surface): 1–2 coats. If the existing paint is sound and the colour change is subtle, 1 coat of premium paint may suffice.
- Changing from dark to light colour: 2–3 coats, or prime first with white tinted primer to reduce the number of finish coats needed.
- New plaster or bare drywall: 1 coat diluted primer (10–20% water) to seal the porous surface, then 2 coats of finish. Skipping the primer on new plaster leads to uneven absorption and patchy results.
- Deep, rich, or dark colours: 2–3 coats - pigment-heavy colours often have lower opacity per coat.
Interior vs Exterior Paint - Key Differences
These are not interchangeable products despite looking similar:
- Interior paint is formulated for low VOC, easy cleaning, and colour consistency in controlled environments. It will fade, crack, and peel when exposed to UV, moisture, and temperature variation outdoors - sometimes within a few months.
- Exterior paint contains fungicide (prevents mould and mildew growth), UV stabilisers (prevents fading), and flexible binders that accommodate thermal expansion and contraction. Never substitute interior paint for exterior applications.
- Coverage: Exterior paint typically covers 8–12 m²/L vs 12–15 m²/L for interior - it has a heavier pigment load needed for durability and opacity in outdoor conditions.
- Application: Exterior paint should be applied in dry weather above 10°C and allowed to cure fully (typically 2–4 weeks) before exposure to rain or extreme temperatures.
How this calculator works, and where the numbers come from
The Paint Calculator applies the standard formula for this calculation to the values you enter and updates the result as you type. The calculation itself happens in your browser, and the page explains the method so you can check any result by hand.
Please note: Results are estimates. Add allowance for waste and check product labels and local building codes before you buy or build.
Sources and further reading
Learn more
Read our guide: How Much Paint, Flooring and Concrete Do You Actually Need?