Paint Coverage Rates and Estimating Litres per Coat
The number on the tin is a theoretical maximum on a perfect surface. Real coverage is 20–40% lower, and the difference is predictable.
Theoretical spreading rate
Example: a coating with 45% volume solids at 40 µm DFT → (45 × 10) / 40 = 11.25 m²/L.
Practical spreading rate
| Application | Typical loss factor |
|---|---|
| Brush / roller, smooth surface | 0.05–0.15 |
| Roller, textured / masonry | 0.15–0.30 |
| Air spray, enclosed | 0.25–0.40 |
| Air spray, structural steel outdoors | 0.40–0.60 |
Porosity and first coats
The first coat on bare plaster, concrete, or wood absorbs more — apply a manufacturer’s absorption allowance (often 15–25% extra) or a dedicated sealer/primer that is formulated for it. Subsequent coats sit on a sealed surface and hit closer to the practical rate.
Typical practical rates (reference)
| Product | Practical m²/L per coat |
|---|---|
| Masonry sealer / primer | 6–10 |
| Emulsion (latex) finish | 10–14 |
| Alkyd enamel | 12–16 |
| Epoxy floor coating | 4–7 |
EngEst Pro’s Painting Calculator applies practical spreading rates by product and application method to your surface areas, adds a first-coat absorption allowance, and returns litres and tins per coat in the BOM.
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