# Surface Tension Calculator

URL: https://speedycalculator.com/calculators/physics/surface-tension/
Last updated: 2026-10-30

> The surface tension calculator finds a liquid's surface tension from the force on a film (or wire frame), or from the pressure difference across a droplet, bubble or liquid jet.

## Inputs

- Method
- Force on the film (mN, N, µN)
- Length of the wire (cm, mm, m, in, ft)
- Pressure difference ΔP (Pa, kPa, mbar)
- Radius r (mm, cm, m, in, µm)

## Results

- Surface tension γ
- Comparable to

## Formula

```
Film: γ = F/(2L) · Droplet: γ = ΔP·r/2 · Soap bubble (two surfaces): γ = ΔP·r/4 · Cylindrical jet: γ = ΔP·r
```

## Explanation

Surface tension lets insects walk on water, pulls droplets into spheres and makes small bubbles push harder than large ones. Water's surface tension is about 72 mN/m at room temperature.

### How to use the Surface Tension Calculator

- **Method**
- **Force on the film**
- **Length of the wire**
- **Pressure difference ΔP**
- **Radius r**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Choose the method and enter the values.

### Common mistakes to avoid

- Mixing units between fields.
- Using a rule outside the range where it applies.
- Expecting fun estimates to be exact predictions.

### Inputs explained

FieldWhat to enterMethodChoose one: Film on a wire frame, Liquid droplet, Soap bubble, Liquid jet (cylinder)Force on the filmUnits: mN, N, µNLength of the wireUnits: cm, mm, m, in, ftPressure difference ΔPUnits: Pa, kPa, mbarRadius rUnits: mm, cm, m, in, µm

### Example values

How the main result changes when **Force on the film** changes and everything else stays at the example values above:

Force on the film (mN)Surface tension γ (mN/m)1.45722.18722.9723.63724.35725.872

## Worked example

Inputs — Method: Liquid droplet; Pressure difference ΔP: 144 Pa; Radius r: 1 mm.

Results — **Surface tension γ = 72 mN/m**; Comparable to = Water.

## Key terms

- **Laplace pressure**: Pressure difference across a curved liquid surface.

## FAQ

**Why do small bubbles have higher pressure?**
Laplace pressure is inversely proportional to radius.

**Why does a soap film count twice?**
It has two surfaces.

**What lowers surface tension?**
Soap, detergents, alcohol and heat.

**What is water's surface tension?**
About 72 mN/m at 25 °C.


## Sources

- [OpenStax – University Physics Volume 1](https://openstax.org/details/books/university-physics-volume-1)
- [HyperPhysics (Georgia State University)](http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html)