Paint Coverage Rates: How Much Paint Do I Need Per Square Metre?

Summary

Getting paint quantities right is fundamental to accurate quoting. Over-order and you're absorbing cost on leftover materials; under-order and you have a half-finished job and a trip to the merchants. Most experienced decorators work from coverage rates memorised over time, but having the numbers to hand speeds up estimating and justifies material costs to customers.

Coverage rates vary by product type, substrate porosity, application method, and colour. A matt emulsion on new plaster covers far less per litre than the same paint on a previously painted surface — the first coat soaks into the substrate. Similarly, a brush-applied coat covers less area per litre than a roller coat (brush leaves a thicker film), which matters for accurate material estimates.

This article gives the reference coverage rates for all common paint products used on UK residential and commercial decorating work, plus the calculation method for each surface type.

Key Facts

• Theoretical vs practical coverage — manufacturers state theoretical coverage on a smooth, non-porous, previously painted surface; real coverage on site is typically 10-20% less
• Coverage on new plaster — first coat (mist coat) absorbs heavily; assume 8-10m²/L; subsequent coats normal
• Coverage on rough/textured surfaces — masonry paint on rough render: as low as 4-6m²/L with a thick-pile roller; smooth render: 10-12m²/L
• Brush vs roller — brush applies a thicker film and uses more paint per m²; roller slightly more economical
• Tinted colours — deep base colours have lower opacity; plan for 3 coats on dark or vibrant colours; allow less coverage per coat
• Add 10% waste — always add minimum 10% for waste, drips, roller trays, and touching up
• Tin sizes — most trade paints come in 2.5L and 5L; plan towards the nearest tin size up
• Wallpaper paste (size) — apply before lining paper or wallpaper; coverage approximately 30-50m² per pack

Quick Reference Table

Detailed Guidance

Standard Room Calculation

Walls:

1. Measure room perimeter: add all wall lengths together (e.g. 4m + 4m + 3m + 3m = 14m)
2. Multiply by ceiling height (e.g. 14m × 2.4m = 33.6m²)
3. Subtract openings: standard door ≈ 2m²; window ≈ 1.5m²; French door ≈ 3.5m²
4. Divide by coverage rate for chosen product
5. Multiply by number of coats
6. Add 10%

Example — lounge repaint, 4m × 3.5m × 2.4m:

• Wall area: (4 + 3.5) × 2 × 2.4 = 36m²
• Less 1 door + 2 windows: 36 - (2 + 3) = 31m²
• Coverage (trade matt at 13m²/L): 31 ÷ 13 = 2.38L per coat
• Two coats: 4.76L
• Add 10%: 5.24L → buy 2 × 2.5L tins (5L) and one extra 2.5L

Ceiling:

• Area: 4m × 3.5m = 14m²
• One coat at 13m²/L = 1.08L; two coats = 2.16L + 10% = 2.38L → buy 1 × 2.5L

Woodwork Calculation

Woodwork is harder to calculate precisely because of the complex shapes involved. Use these standard allowances per item:

For an average three-bedroom house full woodwork repaint (skirtings, doors, architraves, window frames):

• Allow approximately 25-35m² total painted surface
• Three coats (undercoat + 2 gloss): 75-105m² total coat coverage
• At 12m²/L for satinwood: 6.25-8.75L
• Typically buy 3 × 2.5L tins (7.5L) plus a 1L for touch-ups

Calculating for New Plaster

New plaster requires a mist coat before full coats. The mist coat is diluted paint (not a separate product) and covers less than repaint:

For a new plastered room, budget approximately 25% more paint than the equivalent repaint job.

Multi-Coat System Totals

These are typical system totals for common work types:

Frequently Asked Questions

Why does the tin say 14m²/L but I'm only getting 10m²?

Manufacturer coverage rates are measured under ideal test conditions — smooth, non-porous, horizontal surface in controlled temperature. On site, factors that reduce coverage include: surface porosity, rough texture, roller nap thickness, brush type, application speed, and temperature. Always use real-world rates in your estimates (10-15% below stated rate on smooth surfaces; 20-30% below on porous or textured).

Should I buy a bit extra as contingency?

Always add 10% minimum. If working with a custom tinted colour that cannot be easily re-matched, add 15-20% — tinting batches may vary slightly, and touching up with a different batch is noticeable. Keep leftover paint in labelled, sealed tins for customer touch-ups.

How do I calculate curved or complex surfaces?

For complex shapes, break them down into simple rectangles and triangles. A ceiling rose is approximately circular — use πr² for the area. A curved bay window: measure the total length of all faces and multiply by height. For very complex surfaces, add a 20% contingency rather than trying to measure exactly.

Does spraying use more or less paint than rolling?

Airless spraying typically uses 15-25% more material than rolling due to overspray and the thinner films applied per pass. You may need additional coats to achieve equivalent hiding power. However, spraying is faster for large areas. See spraying vs rolling for a full comparison.

Regulations & Standards

• BS EN 13300 — includes classification of spreading rate (coverage) and hiding power (opacity) for water-borne decorative paints

• NBS Specification — many specifiers reference coverage rates in architectural specifications; use manufacturer's stated rates with allowances

• Dulux Trade Coverage Calculator — online tool for common rooms

• Johnstone's Trade Coverage Guide — product-by-product coverage reference

• Paint Quality Institute — Application Guide — general guidance on coverage and application

• interior emulsion — which emulsion to choose for each room type

• exterior masonry — coverage rates and calculations for exterior masonry

• woodwork prep — product system for woodwork

• spraying vs rolling — how application method affects paint consumption