Paint Spreading Rate Calculator
What is the Spreading Rate of Paint?
The spreading rate of paint refers to the surface area that a specific volume of paint can cover. It is the most critical metric for professional painters and DIY enthusiasts to determine how much paint is required for a project. Understanding the spreading rate ensures you don't run out of paint mid-job or waste money on excessive inventory.
The spreading rate is typically expressed in square meters per liter (m²/L) or square feet per gallon (sq ft/gal). Manufacturers provide a "theoretical spreading rate" on the can, but the "actual spreading rate" often varies due to surface texture and application methods.
The Paint Spreading Rate Formula
To calculate the spreading rate of the paint you have already applied, use the following simple formula:
Factors That Affect Paint Coverage
- Surface Porosity: Highly porous surfaces like new plaster, brick, or unprimed wood "drink" more paint, reducing the spreading rate.
- Surface Texture: Rough or corrugated surfaces have more actual surface area than a flat measurement suggests.
- Application Method: Spraying often uses more paint than rolling or brushing due to overspray.
- Number of Coats: The spreading rate usually improves on the second coat because the surface is already sealed.
Practical Example
Scenario: You painted a room with a total wall area of 40 square meters. By the time you finished one complete coat, you had used exactly 4 liters of paint.
Calculation: 40 m² ÷ 4 Liters = 10 m²/L.
If the paint manufacturer claimed a rate of 12 m²/L, your specific surface was slightly more absorbent than their lab-tested surface.
Typical Coverage Rates for Common Paints
| Paint Type | Average Spreading Rate (m²/L) | Average Spreading Rate (sq ft/gal) |
|---|---|---|
| Emulsion (Wall Paint) | 10 – 12 | 350 – 450 |
| Gloss / Satin (Wood & Metal) | 12 – 15 | 450 – 550 |
| Primer / Undercoat | 8 – 10 | 300 – 350 |
| Masonry Paint | 6 – 8 | 200 – 300 |
How to Estimate Paint Needed Before Buying
To estimate how much paint to buy, reverse the formula:
Paint Required = (Total Area × Number of Coats) ÷ Manufacturer's Spreading Rate
Always add a 10% "buffer" to your final volume to account for spills, touch-ups, and surface variations.