Staring at empty walls and wondering how much paint to buy? You're not alone. Over-buying wastes money, while under-buying means extra trips to the store and potential color matching issues. Let's solve this once and for all.
Quick Answer: Use a Paint Calculator
The fastest way to calculate paint needed is with our Paint Calculator. Just enter your room dimensions, and it accounts for:
- Wall and ceiling area
- Doors and windows
- Number of coats
- Paint coverage rate
Average room (3.7Ă—3.7 m, 2.4 m ceiling): 7.6-11.4 litres for walls, 3.8 litres for ceiling.
Step-by-Step: Calculate Paint Manually
If you prefer to calculate by hand, here's the formula professionals use:
Step 1: Measure Your Room
You'll need:
- Length of each wall
- Ceiling height
- Number and size of doors
- Number and size of windows
Pro tip: Round measurements up to the nearest foot to account for waste.
Step 2: Calculate Wall Area
Formula: (Length + Width) Ă— 2 Ă— Height
Example: 3.7 m Ă— 4.6 m room with 2.4 m ceilings
- (3.7 + 4.6) × 2 × 2.4 = 39.8 m²
Step 3: Subtract Doors and Windows
Standard sizes:
- Door: 1.9 m²
- Window: 1.4 m²
Example: Room with 2 doors and 2 windows
- 39.8 - (2×1.9) - (2×1.4) = 33.2 m²
Step 4: Calculate Ceiling Area (if painting)
Formula: Length Ă— Width
Example: 3.7 × 4.6 = 17.0 m²
Step 5: Divide by Coverage Rate
Standard coverage: 32.5-37 m² per 3.8 litres
For walls: 33.2 Ă· 32.5 Ă— 3.8L = 3.9 litres (buy 7.6 litres for 2 coats)
For ceiling: 17.0 Ă· 32.5 Ă— 3.8L = 2.0 litres (buy 3.8 litres)
Step 6: Multiply by Number of Coats
Most projects need:
- Primer: 1 coat
- Finish paint: 2 coats
- Dark colors over light: 3 coats
Paint Coverage: What Affects It?
Not all paint covers equally. Here's what changes the numbers:
Paint Quality
- Premium: 37-42 m²/4L
- Standard: 32-37 m²/4L
- Economy: 23-32 m²/4L
Surface Texture
- Smooth drywall: Maximum coverage
- Textured walls: Reduce by 20%
- Rough stucco: Reduce by 30-40%
- Bare wood: Reduce by 30%
Color Changes
- Light to light: 1-2 coats
- Light to dark: 2-3 coats
- Dark to light: Primer + 3 coats
Pro Tips from Professional Painters
After painting thousands of rooms, here's what we've learned:
1. Always buy extra paint
Order 10-15% more than calculated. Reasons:
- Touch-ups after moving furniture back
- Future repairs and marks
- Color matching is never perfect later
2. Buy from one batch
Paint colors vary slightly between production runs. Buy all your paint at once, from the same batch number.
3. Primer is not optional
Skipping primer costs you more in extra coats. Always prime when:
- Painting bare drywall
- Covering dark colors
- Dealing with stains or water damage
4. Quality paint = fewer coats
Premium paint covers better and lasts longer. The extra $10/gallon pays for itself in labor saved.
5. Ceiling paint is different
Use actual ceiling paint—it's formulated to minimize drips and has better coverage for overhead application.
Common Paint Calculation Mistakes
Mistake #1: Forgetting about trim
Baseboards, crown molding, and window trim add 10-20% to your paint needs. Calculate separately.
Mistake #2: Using wrong coverage rate
Check the can label. Coverage varies by brand and finish (flat covers more than gloss).
Mistake #3: Not accounting for texture
Popcorn ceilings and textured walls use significantly more paint than smooth surfaces.
Mistake #4: Skipping the second coat calculation
Most rooms need 2 coats minimum. Factor this in from the start.
Frequently Asked Questions
How many square feet does a gallon of paint cover?
Standard coverage is 32.5-37 m² per 3.8 litres for one coat on a smooth surface. Premium paints may cover up to 42 m².
How much paint for a 3Ă—3 m room?
Walls only: 5.7-7.6 litres for two coats. With ceiling: Add 3.8 more litres.
How much paint for a 3.7Ă—3.7 m room?
Walls only: 7.6-9.5 litres for two coats. With ceiling: Add 3.8 more litres.
Does primer count as a coat?
No. Primer goes on first, then your finish coats. Budget for primer separately.
How long does paint last?
Unopened cans: 10+ years if stored properly. Opened cans: 2 years in airtight containers. Excess paint is still worth buying for future touch-ups.
Can I return unused paint?
Most stores accept unopened cans within 30-90 days. Custom colors are usually non-returnable. Check your store's policy before buying.
Room-by-Room Paint Estimates
Here are quick estimates for common rooms:
Bedroom (3.7Ă—3.7 m): 7.6-11.4 litres
Living Room (4.6Ă—6 m): 15.1-18.9 litres
Bathroom (2.4Ă—3 m): 3.8-7.6 litres
Kitchen (3Ă—3.7 m): 7.6-11.4 litres
Hallway (0.9Ă—3 m): 3.8 litres
All estimates include two coats on walls, excludes ceiling
Calculate Your Paint Needs Now
Ready to get exact numbers for your project? Our Paint Calculator does the math instantly:
âś“ Enter room dimensions
âś“ Specify doors and windows
âś“ Choose number of coats
âś“ Get gallon estimate immediately
No signup required. 100% free. Works on mobile.
Stop guessing and start painting with confidence. Calculate your paint needs in under 60 seconds.
Last updated: February 2026
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