Calculate surface tension for liquids in different physical configurations. Select a shape (flat film, droplet, hollow bubble, or liquid jet), then enter the force applied and contact length — or for capillary rise, input contact angle, liquid density, and tube radius. Get back the surface tension (γ) in N/m, plus a breakdown of the formula used for your chosen geometry.
Surface Tension (γ)
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Surface Tension (mN/m)
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Formula Applied
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Number of Surfaces
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Surface tension is the tendency of a liquid's surface to resist external forces, caused by cohesive intermolecular forces between liquid molecules. It acts like a thin elastic membrane on the surface, and is measured as force per unit length (N/m).
For a flat film, the formula is γ = F / (2L), because a flat film has two surfaces. Divide the applied force (in Newtons) by twice the contact length (in metres) to get surface tension in N/m.
A liquid droplet has one surface, so γ = F / L. Simply divide the force acting on the droplet by the contact length. This differs from a bubble, which has an inner and outer surface.
A hollow bubble has two surfaces (inner and outer), so the formula is γ = F / (2L) — the same factor-of-two correction as a flat film. Divide the applied force by twice the contact length.
A liquid jet also has two surfaces, giving γ = F / (2L). The jet can be thought of as a cylindrical film with an inner and outer boundary, requiring the same two-surface correction as a flat film or bubble.
Surface tension is expressed in Newtons per metre (N/m) in SI units, or equivalently in millinewtons per metre (mN/m) and dynes per centimetre (dyn/cm). Water at 20 °C has a surface tension of approximately 72.8 mN/m.
Surface tension generally decreases as temperature increases. Higher temperatures increase molecular kinetic energy, weakening the cohesive intermolecular forces responsible for surface tension. This is why hot water cleans better than cold water.
Capillary rise occurs when a liquid climbs up a narrow tube against gravity due to surface tension. The rise height is given by h = (2γ cos θ) / (ρ g r), where θ is the contact angle, ρ is liquid density, g is gravitational acceleration, and r is the tube radius.