How to Work Out Paint Coverage for Protective Coatings

Accurately calculating paint coverage is essential before starting any coating project. Whether you’re coating steel, concrete, wood, or machinery, knowing how much product you need helps ensure proper protection, reduce waste, and control project costs.

At New Guard Coatings, we help customers determine paint quantities and coverage rates for all types of industrial and protective coatings, ensuring every job is completed efficiently and to specification.

What Does Paint Coverage Mean?

Paint coverage refers to the area a specific quantity of paint can cover at a certain film thickness. It’s usually measured in square metres per litre (m²/L) and varies depending on the coating type, surface profile, and application method.

Every coating product includes a theoretical coverage rate in its Technical Data Sheet (TDS), based on an even application and ideal conditions. However, actual coverage achieved on-site is often lower due to application losses, surface roughness, and overspray.

Why Paint Coverage Is Important

Knowing how to calculate paint coverage helps you:

  • Order the correct amount of product for your project

  • Ensure correct film thickness (DFT) for long-term protection

  • Minimise material waste and overspend

  • Plan coating application efficiently

Applying too little paint can leave surfaces under-protected, while applying too much can lead to runs, cracking, or excessive drying times.

How to Calculate Theoretical Paint Coverage

Theoretical coverage can be calculated using this formula:

Theoretical Coverage (m²/L) = (10 × Volume Solids %) / Dry Film Thickness (µm)

For example, if a coating has a volume solids of 60% and is applied at a DFT of 100 microns:

(10 × 60) / 100 = 6 m²/L

This means 1 litre of paint will theoretically cover 6 square metres at 100 microns DFT under ideal conditions.

Allowing for Practical Losses

In real-world applications, you’ll always experience some paint loss due to overspray, uneven surfaces, and absorption. To account for this, apply a loss factor based on your application method:

  • Airless spray: 20–30% loss

  • Brush or roller: 10–20% loss

  • Complex steelwork or irregular surfaces: 30–50% loss

So, if your theoretical coverage is 6 m²/L using airless spray, your practical coverage might be closer to 4.5–5 m²/L.

Other Factors That Affect Paint Coverage

Several site conditions can also influence paint coverage rates:

  • Surface profile and roughness: Coatings on abrasive-blasted steel require more paint to fill the surface peaks and valleys.

  • Porosity: Concrete, timber, and aged substrates absorb more product on the first coat.

  • Temperature and humidity: These can affect paint viscosity, flow, and overspray levels.

  • Application skill: Experienced applicators generally achieve better consistency and less waste.

Using Wet Film Thickness to Check Coverage

During application, you can use a Wet Film Thickness (WFT) gauge to ensure the coating is applied at the correct thickness to achieve the desired DFT once cured.

Use the formula:

WFT = DFT × 100 / Volume Solids (%)

This helps confirm the coating is being applied evenly and at the correct rate for full coverage and protection.

How New Guard Coatings Can Help

At New Guard Coatings, we provide expert guidance to help you calculate paint quantities and coverage for any project. Our team can assist with:

  • Paint coverage estimates and DFT calculations

  • Surface preparation and application advice

  • Selecting the right product for your environment and substrate

We work closely with contractors, applicators, and specifiers to ensure every coating system is applied accurately and performs as designed.

Contact Our Team

For help working out paint coverage or choosing the right coating for your project, contact our technical experts today.