Paint Coverage Calculator: How Many Liters for Your Walls?
Buying too little paint means an extra trip to the hardware store — and the risk of a color batch mismatch that ruins your finish. Buying too much wastes money and leaves you storing hazardous material. Getting the quantity right before you start is the single most underrated step in any painting project. This calculator uses the standard industry formula: Liters = (Wall Area m² ÷ Coverage Rate m²/L) × Number of Coats × Waste Buffer. Enter your wall area, choose the coverage rate from your paint can (or pick a typical value from the dropdown), select how many coats you need, and the tool instantly returns how many liters to buy — including a configurable waste buffer to cover roller splatter and touch-ups. Coverage rates vary by paint type: bargain-bin interior latex typically delivers 8–10 m²/L, a premium acrylic covers 10–12 m²/L, and exterior masonry paint may only reach 6–8 m²/L on porous surfaces. Always use the figure printed on your specific can for the most accurate result.
To calculate how much paint you need: divide the wall area (m²) by the paint coverage rate (m²/L), multiply by the number of coats, and add a 10% waste buffer. Formula: **Liters = (m² ÷ coverage rate) × coats × 1.10**. Standard interior latex (10 m²/L), 2 coats, 10% buffer = **0.22 L per m²**. For a 30 m² room: (30 ÷ 10) × 2 × 1.10 = **6.6 L — buy two 4 L cans**.
When to use this calculator
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Example: 12 m² bedroom
- Walls: 2 × 3.6 m and 2 × 3.3 m, height 2.60 m → perimeter 13.8 m × 2.60 m = 35.88 m²
- Subtract 1 door (1.90 m²) → net area = 33.98 m²
- Settings: standard latex (10 m²/L), 2 coats, 10% waste buffer
- Calculation: (33.98 ÷ 10) × 2 × 1.10 = 3.398 × 2 × 1.10 = 7.48 L
How it works
2 min readHow to calculate how much paint you need
The standard paint quantity formula is:
Total Liters = (Wall Area m² ÷ Coverage Rate m²/L) × Number of Coats × (1 + Waste %/100)Key parameters:
Step-by-step example:
4 m × 4 m room, 2.70 m ceiling, 1 door and 1 window, premium latex (11 m²/L), 2 coats, 10% buffer.
Perimeter = (4 + 4 + 4 + 4) = 16 m
Gross area = 16 m × 2.70 m = 43.2 m²
Door deduction = 1.9 m²
Window deduction = 1.2 m²
Net area = 43.2 − 1.9 − 1.2 = 40.1 m²
Base liters = (40.1 ÷ 11) × 2 = 7.29 L
With 10% buffer = 7.29 × 1.10 = 8.02 L → buy two 4 L cans---
Paint coverage chart: liters needed by area and paint type
| Paint type | Coverage (m²/L per coat) | Recommended coats | 20 m² | 40 m² | 80 m² |
|---|---|---|---|---|---|
| Economy interior latex | 8–10 | 2–3 | 4.8–5.5 L | 9.6–11 L | 19.2–22 L |
| Standard interior latex | 10 | 2 | 4.4 L | 8.8 L | 17.6 L |
| Premium interior latex | 11–12 | 2 | 4.0–4.4 L | 8.0–8.8 L | 16.0–17.6 L |
| Exterior latex (masonry) | 6–9 | 2–3 | 5.5–7.3 L | 11–14.7 L | 22–29.3 L |
| Synthetic enamel | 6–8 | 2 | 5.5–7.3 L | 11–14.7 L | 22–29.3 L |
| Primer / sealer | 10–14 | 1 | 1.6–2.2 L | 3.1–4.4 L | 6.3–8.8 L |
| Ceiling paint (flat white) | 10–12 | 1–2 | 1.8–2.2 L | 3.7–4.4 L | 7.3–8.8 L |
All figures include 10% waste buffer. Source: Sherwin-Williams, Dulux, ASTM paint standards.
> Note: On highly porous surfaces (bare brick, rough render) reduce the effective coverage rate by 20–30% and apply a dedicated primer coat first.
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Quick reference: how much paint for each room type
| Room type | Typical net wall area | Standard latex (2 coats + 10%) |
|---|---|---|
| Small bathroom | 10–15 m² | 2.2–3.3 L |
| Bedroom 3×4 m | 25–30 m² | 5.5–6.6 L |
| Bedroom 4×4 m | 30–38 m² | 6.6–8.4 L |
| Living/dining 5×4 m | 45–60 m² | 9.9–13.2 L |
| Kitchen 3×3 m | 20–28 m² | 4.4–6.2 L |
| Home exterior (small house) | 80–120 m² | 24–36 L (exterior latex) |
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Common mistakes when calculating how much paint to buy
1. Not subtracting doors and windows: A typical room has 3–5 m² of openings — ignoring them adds a full extra can to your purchase.
2. Using label coverage without adjusting for porosity: New render or unprimed brick absorbs 25–35% more paint. Always prime first.
3. Planning for only one coat: A single coat of standard latex rarely achieves uniform opacity. Two coats is the professional minimum.
4. Confusing kg with liters: Some paints are sold by weight. Latex density is roughly 1.3–1.5 kg/L, so 4 kg ≈ 2.7–3.1 L, not 4 L.
Frequently asked questions
How do I calculate how many liters of paint I need for my walls?
The formula is: Liters = (Wall Area m² ÷ Coverage Rate m²/L) × Number of Coats × (1 + Waste%/100). If your room has 60 m² of net wall area and your paint covers 10 m²/L, you need (60 ÷ 10) × 2 × 1.10 = 13.2 L for two coats with a 10% buffer. Always measure wall area carefully: multiply perimeter by ceiling height, then subtract doors and windows.
How many liters of paint do I need for a room?
For a typical bedroom (about 30 m² of net wall area) with standard interior latex (10 m²/L), 2 coats, and 10% waste buffer: (30 ÷ 10) × 2 × 1.10 = 6.6 L. Buy two 4 L cans. For a larger room of 40 m² at the same spec: 8.8 L — buy a 10 L can. Use the calculator above for your exact dimensions.
What is the standard paint coverage rate, and why does it vary?
The industry standard for interior latex paint is 10–12 m²/L per coat, but real-world coverage depends on four key variables: (1) Surface porosity — new drywall and bare plaster absorb far more than previously painted walls; (2) Surface texture — rough walls have greater actual area, consuming more paint; (3) Application method — rollers are more efficient than brushes on large flat surfaces; (4) Paint solids content — higher-quality paints have more pigment and cover better per liter. Always check the technical data sheet on the can.
Do I always need two coats of paint?
In most cases, yes. A single coat of standard latex rarely achieves full opacity or an even finish, particularly when changing from a dark to a light color, covering water stains, painting over a glossy surface (without sanding first), or using a deeply saturated color. Two coats is the professional standard. The one exception is touch-ups on an identical color and finish — one coat may blend adequately there.
What is the difference between primer and finish paint coverage?
Primers typically cover 10–14 m²/L because they're formulated to penetrate and seal the surface rather than build color depth — they're thinner and more fluid. Finish paints cover 8–12 m²/L and contain pigment and binders for color accuracy and durability. Always calculate primer and finish paint separately using each product's own coverage rate from the label.
How much extra paint should I buy as a buffer?
The standard professional recommendation is a 10% waste allowance on top of your calculated need. This covers: roller splatter and tray residue (3–5%), touch-up patches after the main job, uneven application in corners and edges, and small measurement inaccuracies. Round your final liter count up to the nearest available can size and save any leftover paint in a well-sealed, labeled container for touch-ups.
How does surface texture affect how much paint I need?
Texture dramatically affects consumption. As a practical guide: Smooth gypsum board or previously painted flat wall — use the label coverage rate as stated. Light texture (orange peel or fine stipple) — reduce effective coverage by 10–15%. Medium texture (knockdown or sand finish) — reduce by 20–25%. Heavy texture (rough plaster or exterior brick) — reduce by 30–40% and consider a fill primer before painting.
Should I subtract doors and windows from my wall area?
Yes — always subtract opening areas for an accurate estimate. A standard interior door is approximately 0.9 m × 2 m = 1.8 m². A standard window is roughly 1.2 m × 1.0 m = 1.2 m². For a room with one door and two windows, subtract about 4.2 m² from your total wall area. Some painters skip this step and treat openings as a natural waste buffer — both approaches are valid, but don't subtract openings and add a 10% buffer simultaneously, as that double-counts the margin.
How do I calculate paint for a ceiling separately from walls?
Ceiling paint is always calculated separately. Multiply room length × width to get ceiling area. For a 4 m × 5 m room: 20 m². At 12 m²/L ceiling paint and two coats with 10% buffer: (20 ÷ 12) × 2 × 1.10 = 3.67 L. Ceilings typically use flat-finish white paint — a different product from wall paint with its own coverage rate. If your ceiling is vaulted or sloped, measure it as a series of rectangles or triangles.
What is the difference in coverage between interior and exterior paints?
Exterior paints generally cover 8–10 m²/L versus 10–12 m²/L for interior paints, for two reasons: exterior surfaces are usually rougher and more porous, and exterior formulations contain more flexible resins and UV stabilizers that add density. When estimating exterior paint, always factor in surface condition — a newly rendered wall may achieve 9 m²/L, while a weathered porous brick facade may only deliver 6–7 m²/L and require a masonry sealer as a first step.