Paint Coverage Calculator
Estimate paint required in liters and gallons for walls and rooms with doors, window deductions, and coats.
Last verified: September 2026Inputs & Parameters
Calculation Results
Theoretical surface volume estimate including selected contingency waste allowance.
Retail Container Options (Alternative Purchasing Scenarios)
Purchase one of these alternative packaging options (each rounded up to whole cans):
Paint Volume Calculation & Surface Coverage Guide
Calculating paint requirements requires determining the net paintable surface area of all target walls and ceilings, deducting unpainted openings (such as windows and entry doors), and multiplying by the desired number of coats. Accurate estimation prevents both costly paint shortages and expensive leftover waste.
Surface Measurement Formulas
- Gross Wall Area:
Perimeter × Ceiling Height = 2 × (Length + Width) × Height - Ceiling Area:
Length × Width - Openings Deduction:
(Doors × Door Area) + (Windows × Window Area) - Net Paintable Area:
(Gross Walls + Ceiling Area) - Deductions - Paint Volume Needed:
(Net Area × Number of Coats) / Coverage Rate per Can
Standard Coverage Benchmarks
| Unit System | Standard Container | Typical Coverage Rate | Standard Opening Allowances |
|---|---|---|---|
| Imperial | 1 Gallon (128 fl oz) | 350 to 400 sq ft / gallon | Door: ~21 sq ft (3'×7') | Window: ~15 sq ft (3'×5') |
| Metric | 1 Liter | 10 to 12 m² / liter | Door: ~1.9 m² (0.9m×2.1m) | Window: ~1.4 m² (1.2m×1.2m) |
Number of Coats & Surface Porosity
Unprimed drywall, textured masonry, and stark color transitions (e.g. painting white over dark navy) absorb significantly more paint and typically demand a primer coat plus 2 finish coats. Pre-painted smooth walls in good condition usually achieve full coverage with 2 standard coats.
Worked Example
A 14 ft × 12 ft room with 9 ft ceilings, 1 standard door, 2 windows, requiring 2 coats on walls only (coverage: 350 sq ft/gal):
1. Wall Perimeter = 2 × (14 + 12) = 52 ft; Gross Area = 52 × 9 = 468 sq ft
2. Deductions = (1 × 21 sq ft) + (2 × 15 sq ft) = 51 sq ft
3. Net Wall Area = 468 - 51 = 417 sq ft
4. Total Surface to Paint (2 Coats) = 417 × 2 = 834 sq ft
5. Exact Theoretical Paint Needed = 834 / 350 = 2.38 gallons (9.01 liters)
6. Retail Purchasing Scenarios (Alternative Options — do not combine):
• If purchasing 1-gallon cans: ceil(2.38) = 3 Gallon Cans
• If purchasing 5-liter cans: ceil(9.01 / 5) = 2 Five-Liter Cans
• If purchasing 1-liter cans: ceil(9.01) = 10 One-Liter Cans