Pressure Difference Between the Inside and the Outside of a Liquid Droplet

Laplace pressure jump for a spherical droplet

\( \displaystyle \Delta p \;=\; p_i - p_{\text{atm}} \;=\; \frac{2\sigma}{R} \)

Symbols

\(\Delta p\) — gage pressure (Pa)
\(p_i\) — pressure inside the droplet (Pa)
\(p_{\text{atm}}\) — ambient atmospheric pressure (Pa, reference)
\(\sigma\) — surface tension (N·m\(^{-1}\))
\(R\) — droplet radius (m)

Spherical droplet schematic with pressure arrows

Fluid preset (σ at 20 °C)

Choose a preset or pick Custom… to edit σ.

Surface tension, σ (N/m)

Radius, R

Plot range: 5–100 μm. Use the slider or drag the red dot.

Current values

Δp (Pa)

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Δp (kPa)

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Δp (psi)

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Linear axes. Smaller \(R\) ⇒ larger \(\Delta p\). We treat atmospheric pressure as the reference (\(p_{\text{atm}}\)), so \(\Delta p\) is the gage pressure inside the droplet.

This demo uses \(\Delta p = p_i - p_{\text{atm}} = 2\sigma/R\) for a spherical, static interface (gravity and viscosity neglected).