What is surface tension?

Surface tension is the energy per unit area (or equivalently force per unit length) at a liquid interface. It arises because molecules at the surface have fewer neighbors and therefore higher potential energy than interior molecules.

What are the two calculation methods?

F/L: place a wire of known length L at the surface and measure the pull force F. E/A: measure how much energy E is needed to increase the surface area by A. Both give γ in N/m.

How do N/m, mN/m, and dyn/cm relate?

1 N/m = 1000 mN/m = 1000 dyn/cm. The CGS unit dyn/cm is still common in older literature; water at 20°C is ~72.8 mN/m = 72.8 dyn/cm.

Why does temperature matter?

Surface tension decreases nearly linearly with temperature. The reference values shown here are at 20°C (68°F). For precise work, use temperature-corrected data from your fluid's datasheet.

What is a typical value for water?

Pure water at 20°C has a surface tension of 72.8 mN/m. Adding soap or detergent drops it to 25–40 mN/m, which is why soap helps water wet surfaces more effectively.

Surface Tension Calculator

Name: Surface Tension Calculator
Availability: InStock
Author: Nham Vu

Compute surface tension from force and length or from surface energy and area, with unit conversion for N/m, mN/m, and dyn/cm.

Inputs

Calculation Method

Force (N) ÷ Length (m) — ring or wire pull method

Force (F)

Length (L)

Result

Enter values and press Calculate.

Reference Values at 20°C

Fluid	mN/m	dyn/cm

Highlighted row = closest match to your calculated value.

Summary

Compute surface tension from force and length or from surface energy and area, with unit conversion for N/m, mN/m, and dyn/cm.

How it works

Choose the F/L method (force divided by length) or the E/A method (energy divided by area).
Enter the known values — force (N) and length (m), or energy (J) and area (m²).
The tool divides and converts the result to N/m, mN/m, and dyn/cm simultaneously.
Compare your result against the built-in reference table of common fluids at 20°C.

Use cases

Lab experiments measuring liquid surface tension with a wire or ring.
Checking capillary rise calculations in materials science coursework.
Verifying surface energy measurements in thin-film or coating research.
Quick unit conversion between SI and CGS (dyn/cm) for published data.
Teaching demos comparing water vs. soapy water surface tension.
Engineering estimates for wetting, adhesion, and spreading coefficient problems.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu