What is the wetting coefficient?

The wetting coefficient (spreading coefficient S) quantifies the thermodynamic tendency of a liquid to spread on a solid. S = γ_SV − γ_SL − γ_LV. When S ≥ 0 the liquid spreads completely; when S < 0 it forms a droplet with a finite contact angle.

What units should I use?

All surface tension values should be in millinewtons per meter (mN/m), which is equivalent to dynes per centimeter (dyn/cm). The resulting spreading coefficient is also in mN/m.

How do I find γ_SL if I only know the contact angle?

Use Young's equation: γ_SL = γ_SV − γ_LV × cos(θ), where θ is the equilibrium contact angle. This tool includes a contact angle helper that computes γ_SL for you automatically.

What is a typical surface tension for water?

Water has a liquid-vapor surface tension of about 72.8 mN/m at 20°C. For ethanol it is roughly 22.4 mN/m, and for mercury about 486 mN/m.

Can S be greater than zero for water on glass?

Yes. Glass has a high surface energy (γ_SV ≈ 50–70 mN/m for clean glass) and the solid-liquid interfacial tension is low, so the spreading coefficient for water on clean glass is typically positive, explaining why water spreads and forms thin films on glass.

What is the difference between wetting and adhesion?

Wetting describes whether a liquid spreads spontaneously (governed by S), while adhesion describes the work needed to separate two phases. Both depend on surface tensions, but they answer different practical questions about interfacial behavior.

Wetting Coefficient Calculator

Name: Wetting Coefficient Calculator
Availability: InStock
Author: Nham Vu

Enter solid and liquid surface tensions plus solid-liquid interfacial tension to instantly calculate the wetting (spreading) coefficient.

Surface Tension Inputs

All values in mN/m (= dyn/cm)

Solid-vapor surface tension γ_SV

mN/m

Solid-liquid interfacial tension γ_SL

mN/m

Liquid-vapor surface tension γ_LV

mN/m

Or derive γ_SL from contact angle

degrees

Requires γ_SV and γ_LV to be filled in. Uses Young's equation.

Common presets

Result

Enter surface tension values and click Calculate.

Typical Surface Tension Values

Liquid	γ_LV (mN/m)
Water (20 °C)	72.8
Ethanol	22.4
Glycerol	63.4
n-Hexane	18.4
Mercury	486.0
Acetone	23.7

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Summary

Enter solid and liquid surface tensions plus solid-liquid interfacial tension to instantly calculate the wetting (spreading) coefficient.

How it works

Enter the solid-vapor surface tension (γ_SV) in mN/m.
Enter the solid-liquid interfacial tension (γ_SL) in mN/m.
Enter the liquid-vapor surface tension (γ_LV) in mN/m.
The calculator applies S = γ_SV − γ_SL − γ_LV instantly.
A positive S means complete wetting (spreading); negative S means partial wetting or no spreading.
Use the contact angle field as an alternative — the tool converts it to γ_SL via Young's equation.

Use cases

Determine whether a coating or adhesive will spread on a substrate.
Evaluate ink wettability on paper or plastic films.
Assess lubricant spreading on metal surfaces.
Screen cleaning agents for their ability to wet and remove contaminants.
Research surfactant formulations and surface treatments.
Teach wettability concepts in physical chemistry courses.
Compare water vs. organic solvent spreading on polymer films.
Quality control of surface energy treatments like plasma or corona.

Frequently Asked Questions

Last updated: 2026-06-18 · Reviewed by Nham Vu