# Surface Tension Calculator

Created by Rahul Dhari
Reviewed by Steven Wooding
Last updated: Nov 13, 2022

The surface tension calculator will help you determine the surface tension for liquid in various forms. Examples of surface tension include water droplets, bubbles, and floating objects. Surface tension in chemistry has been used to explain some intricate concepts like capillary action and floatation of insects.

Surface tension is a function of the surface's force and length. Read on to understand what surface tension is and what causes surface tension.

Before you confuse surface tension with surface area, we would also suggest looking at surface area calculator.

## What does surface tension means?

Surface tension is defined as the tendency of the liquid to resist any external force by forming a thin membrane. This is caused by the presence of cohesive forces between the liquid molecules. A liquid that has large intermolecular forces has higher surface tension. The hydrogen-hydrogen bond in water has very high energy, and therefore, the water has high surface tension compared to other liquids.

The unit of surface tension is force per unit length, i.e., newtons per meter (N/m). Alternatively, the surface tension can also be measured as energy per unit area, i.e., joules per meter square (J/m²). The surface tension formula for a liquid contained in a rectangular container with three fixed sides having length $\text L$ is:

• $\text T_\text{flat} = 0.5 \times \text F / \text L$

where $\text F$ is the force acting on the surface, and $\text T_\text{flat}$ is the surface tension. The surface tension of a liquid is an intrinsic property depending upon its temperature, composition, and molecular activity.

The surface tension decreases with an increase in temperature due to the weakening of cohesive forces as a result of increased thermal activity between molecules. The surface tension calculator will let you estimate the surface tension of a droplet, bubble, jet, or flat surface.

Let's look at how the calculation of surface tension is performed for different cases:

Droplets: These are formed due to the surface tension as it minimizes the surface area and reduces the wall tension of the surface layer. Consider a spherical droplet having a diameter D and internal pressure P. The surface tension on the droplet is given by the surface tension formula:

• $\text T_\text{drop} = \text P \times \text D / 4$

where the pressure $\text P$ is related to the pressure force $\text F$ as:

• $\text F = \text P \times \pi \times \text D^2 / 4$

Hollow bubble: A hollow bubble has two surfaces that are subjected to surface tension. Both the internal and external surface has contact with the air. The definition of surface tension on either side of the bubble having a diameter D is given as:

• $\text T_\text {bub} = \text P \times \text D / 8$

where the pressure $\text P$ is the difference between the internal and atmospheric pressure. Interestingly, the surface tension on the surface of the bubble is half of the surface tension on the droplet.

Liquid jet: A liquid jet is a steady stream of fluid. Consider a jet with diameter D and length L. The surface tension formula is given by the equation:

• $\text T_\text {jet} = \text P \times \text D / 2$

If you are interested, we also have a tension calculator that determines the tension force in a string or rope used to life an object.

## How to calculate surface tension?

To calculate surface tension:

1. Select the shape from the list, say Droplet.
2. Enter the diameter of the droplet.
3. Insert the pressure intensity inside the droplet.
4. The surface tension calculator will return the force and the surface tension for the droplet.

## Example: Using the surface tension calculator

Estimate the surface tension on the soap bubble having an inside-to-outside pressure difference of 2.5 Pa and a diameter of 40 mm.

To calculate surface tension:

1. Select the shape from the list, Bubble.

2. Enter the diameter of the bubble: D = 40 mm.

3. Insert the pressure intensity inside the bubble as 2.5 Pa.

4. Using the surface tension formula:

$\text T_\text{bub} = \text P \times \text D / 8 = 2.5 \times 40 \times 10^-3 / 8 = 0.0125 \text{ N/m}$

The surface tension on the soap bubble is 0.0125 N/m.

We have a vapor pressure of water calculator as well if you ever wonder about things like the vapor pressure of water and ice.

## FAQ

### What is surface tension?

The property of a liquid to act as a thin membrane at the interface or surface. The top layer acts as an elastic sheet due to this phenomenon.

### What are the units of surface tension?

Surface tension is measured in units of force per unit length or energy per unit area. Therefore, the units for surface tension are newtons per meter or joules per square meter.

### How do I calculate surface tension on a bubble?

To calculate surface tension on a bubble:

1. Multiply the pressure difference inside the bubble (compared to outside) by the diameter of the bubble.
2. Divide the product by 8 to get the surface tension.

### How do I calculate surface tension on a liquid jet?

To calculate surface tension on a liquid jet:

1. Multiply pressure inside the jet by the diameter of the jet.
2. Divide the product by 2 to get the surface tension.
Rahul Dhari
Shape
Droplet
Diameter of droplet (D)
in
Pressure inside droplet (P)
psi
Force due to surface tension (F)
lbf
Surface tension (T_drop)
lbf/in
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