Paint Calculator: How Much Paint Do I Need for a Room?
Standing in the paint aisle wondering how many cans to buy is a universal experience. Buy too little and you'll be rushing back mid-project. Buy too much and you've wasted $50+ on paint that'll sit in your garage for years. This guide will teach you exactly how to calculate paint quantities like a pro.
The Basic Paint Formula
Paint coverage is generally standardized: 1 liter covers approximately 10 square meters (or 100 square feet) per coat. Most rooms need 2 coats. The formula is:
Paint Needed (L) = (Wall Area / 10) × Number of Coats
Step 1: Calculate the Wall Area
To calculate wall area, measure the perimeter of the room and multiply by the ceiling height:
Wall Area = Perimeter × Height
For a rectangular room: Perimeter = 2 × (Length + Width)
| Room Size | Perimeter | Height | Wall Area | Paint (1 coat) | Paint (2 coats) |
|---|---|---|---|---|---|
| 4m × 3m | 14m | 2.4m | 33.6 m² | 3.4 L | 6.8 L |
| 5m × 4m | 18m | 2.4m | 43.2 m² | 4.3 L | 8.6 L |
| 6m × 5m | 22m | 2.7m | 59.4 m² | 5.9 L | 11.8 L |
| 10ft × 12ft | 44ft | 8ft | 352 ft² | 3.5 L | 7.0 L |
Step 2: Subtract Windows and Doors
Don't paint your windows and doors (unless you are painting the trim, which requires a different calculation). Subtract these areas from your wall area:
- Standard door: ~1.6 m² (17 ft²) �subtract per door
- Standard window: ~1.2 m² (13 ft²) �subtract per window
- Large window: ~2.0 m² (22 ft²) �subtract per window
- French doors: ~3.0 m² (32 ft²) �subtract per set
| Feature | Subtract (m²) | Subtract (ft²) |
|---|---|---|
| Standard door | 1.6 | 17 |
| Standard window | 1.2 | 13 |
| Large picture window | 2.0 | 22 |
| Sliding glass door | 3.5 | 38 |
Step 3: Calculate Ceiling Area
Ceilings are typically painted separately (and often with flat white paint). Calculate:
Ceiling Area = Length × Width
| Room Size | Ceiling Area | Paint (1 coat) | Paint (2 coats) |
|---|---|---|---|
| 4m × 3m | 12 m² | 1.2 L | 2.4 L |
| 5m × 4m | 20 m² | 2.0 L | 4.0 L |
| 6m × 5m | 30 m² | 3.0 L | 6.0 L |
Step 4: Complete Example Calculation
Let's work through a complete example for a 5m × 4m bedroom with 2.4m ceilings, one door, and two standard windows:
| Step | Calculation | Result |
|---|---|---|
| Room perimeter | 2 × (5 + 4) | 18m |
| Gross wall area | 18 × 2.4 | 43.2 m² |
| Subtract door | 43.2 - 1.6 | 41.6 m² |
| Subtract 2 windows | 41.6 - (2 × 1.2) | 39.2 m² |
| Paint for walls (2 coats) | (39.2 / 10) × 2 | 7.84 L |
| Ceiling paint (2 coats) | ((5 × 4) / 10) × 2 | 4.0 L |
| Total paint needed | 7.84 + 4.0 | 11.84 L |
Common Paint Can Sizes
| Can Size | Volume | Coverage (1 coat) | Coverage (2 coats) |
|---|---|---|---|
| Sample pot | 0.2 - 0.5 L | 2-5 m² | 1-2.5 m² |
| Small can | 1 L | 10 m² | 5 m² |
| Standard can | 2.5 L | 25 m² | 12.5 m² |
| Large can | 5 L | 50 m² | 25 m² |
| Extra large | 10 L | 100 m² | 50 m² |
Factors That Affect Paint Coverage
- Surface texture: Smooth walls need less paint than textured surfaces. Rough or porous surfaces can use 10-20% more paint per coat.
- Color change: Painting a dark color (navy, red) over white requires more coats (3+). Painting light over dark requires primer + 2-3 coats.
- Paint quality: Higher-quality paints typically have better coverage and may stretch further than budget paints.
- Application method: Spraying uses 20-30% more paint than rolling. Brush application is most efficient but slowest.
- Primer usage: Primer is separate from paint. One coat of primer covers ~10 m² per liter, same as paint.
Buying Recommendations by Room Type
| Room Type | Typical Size | Walls (2 coats) | + Ceiling (2 coats) | Recommended Purchase |
|---|---|---|---|---|
| Small bathroom | 2.5m × 2m | 3.5 L | 1.0 L | 1× 5L can (covers both) |
| Small bedroom | 3m × 3.5m | 4.8 L | 2.1 L | 1× 5L walls + 1× 2.5L ceiling |
| Standard bedroom | 4m × 4.5m | 7.0 L | 3.6 L | 2× 5L cans |
| Living room | 5m × 6m | 10.5 L | 6.0 L | 3× 5L cans |
| Open plan | 7m × 6m | 14.0 L | 8.4 L | 4× 5L cans |
Quick Estimation Shortcuts
- Small room (3m × 3m): ~5L for walls (2 coats)
- Medium room (4m × 4m): ~8L for walls (2 coats)
- Large room (5m × 5m): ~12L for walls (2 coats)
- Ceiling: Room area ÷ 5 = Liters needed (2 coats)
Using QuickMath's Paint Estimator
Instead of manual calculations, use our Tile & Paint Estimator. Enter your room dimensions and get instant paint estimates for 1 and 2 coats, plus tile estimates for the same room. It's the fastest way to plan your renovation materials.
Final Tips
- Always buy slightly more paint than calculated �you'll use extra for touch-ups and corners.
- Store leftover paint in a cool, dark place with the lid sealed tight. Label it with the room and date.
- Use primer for drastic color changes or new drywall. It's cheaper than extra coats of premium paint.
- Can't find the exact calculation? Round up to the next standard can size. Unopened cans can be returned.