WFT Calculator

The CoatXpert WFT Calculator helps coating professionals calculate the approximate Wet Film Thickness (WFT) required to achieve a specified Dry Film Thickness (DFT) based on the coating’s volume solids.

WFT is an important parameter in coating application because it provides an immediate target during the application process. By controlling the wet film thickness, applicators can work toward achieving the required dry film thickness after the coating dries or cures.

This calculator is useful for automotive refinishing, industrial coatings, OEM painting, fabrication, maintenance coatings and other professional coating applications.

Note: The calculated WFT is a theoretical estimate. Actual coating behaviour can vary depending on formulation, application method, substrate condition, surface profile, evaporation and process conditions.

What is WFT?

WFT (Wet Film Thickness) is the thickness of a coating immediately after it has been applied and before significant drying or curing occurs.

WFT is commonly measured in micrometres (µm) or mils using a wet film thickness gauge.

For example, if a coating is applied at a WFT of 150 µm, the final dry film thickness will normally be lower because part of the wet coating consists of volatile components that leave the film during drying.

What is Volume Solids?

Volume solids represents the percentage of the wet coating volume that remains as coating film after the volatile components have evaporated.

For example, a coating with 40% volume solids theoretically retains approximately 40% of its wet volume as dry coating film.

For accurate calculations, always use the volume solids value specified in the coating manufacturer’s current Technical Data Sheet (TDS).

How is WFT Calculated?

The basic relationship is:

WFT = Target DFT ÷ Volume Solids Fraction

Where:

Volume Solids Fraction = Volume Solids (%) ÷ 100

For example, suppose the required DFT is 60 µm and the coating has 40% volume solids.

First convert the volume solids percentage:

40 ÷ 100 = 0.40

Then:

WFT = 60 ÷ 0.40

WFT = 150 µm

Therefore, approximately 150 µm WFT is required theoretically to achieve a 60 µm DFT at 40% volume solids.

Why WFT Control is Important

Monitoring WFT during coating application can help the applicator maintain a more consistent film thickness and reduce the risk of applying too much or too little coating.

An excessively high WFT may contribute to problems such as sagging, runs, solvent entrapment or extended drying time, depending on the coating system.

An excessively low WFT may result in insufficient DFT, poor hiding or inadequate coating performance.

The appropriate WFT target should always be considered together with the coating manufacturer’s application recommendations.

µm and Mils Conversion

Coating thickness may be specified using either metric or imperial units.

1 mil = 25.4 µm

For example:

150 µm ≈ 5.91 mils

The CoatXpert WFT Calculator provides both units to make the calculation convenient for different technical specifications and applications.

Important Considerations

The WFT calculated by this tool is based on the theoretical relationship between DFT and volume solids. Actual results may differ because of coating formulation, application efficiency, substrate roughness, spray technique, equipment settings, environmental conditions and measurement method.

For production and quality-control applications, always follow the coating manufacturer’s TDS, application instructions and project specification.

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