Surface Tension Calculator
Work out surface tension instantly with clear inputs, formula shown and shareable results.
About Surface Tension Calculator
Surface tension is force per unit length along a liquid surface. A wire frame pulled from a film has liquid on both sides, so the measured force is divided by twice the wire length. 14.6 mN on a 10 cm wire with two surfaces gives 0.073 N/m, the accepted value for water at 20 C. The same number is the surface energy in joules per square metre.
Formulas
Surface tension
gamma = F / (number of surfaces x L)
Bubble pressure
dP = 4 gamma / r for a soap bubble
Worked example
With the default values below, Surface Tension Calculator returns Surface Tension of 0.07300. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Force measured on the wireminimum 0 N
- 0.0146 N
- Length of the wire in contactminimum 0 m
- 0.1 m
- Number of liquid surfaces pullingaccepts 1–2
- 2
Results
- Surface Tension
- 0.07300 N/m
- Same Value In mN/m
- 73.000
- Excess Pressure In A 1 mm Bubble
- 292.000 Pa
- Surface Energy
- 0.07300 J/m2
Step by step
- 1Values used
- 2Surface tension
- 3Bubble pressure
- 4Surface Tension= 0.07300 N/m
- 5Same Value In mN/m= 73.000
- 6Excess Pressure In A 1 mm Bubble= 292.000 Pa
- 7Surface Energy= 0.07300 J/m2
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why divide by two?
A film has two liquid-air interfaces, one on each side, and both pull on the wire. A single interface, as in a Wilhelmy plate in bulk liquid, uses one.
What is water's surface tension?
About 72.8 mN/m at 20 C - unusually high because of hydrogen bonding, which is why insects can stand on it.