How Much Primer Do I Need?
Quick Answer
~2.5L of primer for a typical room at 10–12m²/L coverage
Based on: 4 walls of a 4m x 3m room at 2.4m height (~30m²), one coat of acrylic primer
How We Calculated This
Primer is applied as a single coat to seal surfaces before the topcoat:
- Wall area: 2 × (4 + 3) × 2.4 = 33.6m²
- Deduct door and window: ~30m²
- Coverage rate: 10–12m²/L (depends on product and surface)
- Primer needed: 30 ÷ 12 = ~2.5L
When Do You Need Primer?
- New plaster: Use a mist coat (diluted emulsion) instead of primer
- Bare wood: Always prime before painting
- Stain blocking: Nicotine, water stains, marker pen
- Colour change: Dark to light colour — grey-tinted primer saves coats
- Bare plasterboard: Prime to even out suction
- Metal surfaces: Use a metal primer to prevent rust
Coverage by Primer Type
- Acrylic primer/undercoat: 12–14m²/L — general purpose, water-based
- Shellac-based primer (Zinsser BIN): 8–10m²/L — best stain blocker
- Oil-based primer/undercoat: 10–12m²/L — good adhesion on difficult surfaces
- PVA sealer: 8–10m²/L — seals porous surfaces
- Metal primer: 10–12m²/L — rust-inhibiting for steel and iron
Tips
For the best results, lightly sand between primer and topcoat with 220-grit sandpaper. Tint your primer towards the topcoat colour for better coverage — most paint shops can tint primer to a mid-tone of your chosen colour. One coat of primer is usually sufficient unless you are blocking heavy stains.