Surface Tension Calculator

Determine surface tension for liquids using the surface tension calculator.

Capillary rise29.7536 mmJurin's law, 2γcos θ/(ρgr). It goes as 1/r, so halving the tube DOUBLES the rise — which is why water climbs so far in fine soil and paper

Contact angle0°below 90°, so the liquid wets the tube and rises

Pressure jump across a curved surface291.2 PaYoung-Laplace, 2γ/r for a drop or a bubble in liquid

Across a soap bubble582.4 PaDOUBLE, because a soap bubble has two surfaces — an inner and an outer film, each contributing

Force to lift a ring of this radius457.4159 µN4πrγ for a du Noüy ring, which wets on both sides

Capillary length2.7273 mm√(γ/ρg) — about 2.7 mm for water. Below this scale surface tension dominates gravity, which is why small drops are spherical and large puddles are flat

Rise in a tube half this size59.5073 mmexactly doubled

Why small bubbles feed large onessmaller means higher pressureΔP goes as 1/r, so a small bubble is at HIGHER pressure than a large one. Connect two and the small one empties into the large one, which is the opposite of most people's intuition

The formula

h = 2γcos θ/(ρgr); ΔP = 2γ/r; soap bubble ΔP = 4γ/r

Everything goes as one over the radius

Capillary rise, the Young-Laplace pressure jump and the curvature force all scale as 1/r. Halving a tube doubles the height water climbs in it, which is why water reaches the top of tall trees through vessels only microns across, and why fine soil holds moisture that coarse sand drains.

Counter-intuitively, a SMALL bubble is at higher pressure than a large one. Connect two bubbles and the small one empties into the large one rather than equalising — the opposite of what most people expect. A soap bubble also has two surfaces, inner and outer, so its pressure jump is 4γ/r rather than 2γ/r.

The capillary length sets the scale

√(γ/ρg) is about 2.7 mm for water. Below that size surface tension beats gravity and drops pull themselves spherical; above it gravity wins and puddles spread flat. That single length explains why raindrops are round and lakes are not.