Young Laplace Equation Calculator
Calculate the pressure difference across a curved fluid interface (droplet, bubble) using the Young-Laplace equation.
Formula
ΔP = 2γ/R (droplet); ΔP = 4γ/R (soap bubble — 2 surfaces)
- γ = surface tension (N/m); R = radius (m).
- Soap bubble has two liquid-air interfaces, so factor is 4γ/R.
- Smaller droplet = higher internal pressure.
- Water surface tension at 20°C ≈ 72.8 mN/m; at 37°C ≈ 70 mN/m.
10 µm water droplet in air
Inputs
- Surface Tension (γ): 72.8 mN/m
- Droplet/Bubble Radius (R): 10 µm
- Interface Type: droplet
ΔP = 2 × 0.0728 / 10×10⁻⁶ = 14,560 Pa ≈ 14.6 kPa.
Frequently asked questions
Why does a soap bubble have 4γ/R instead of 2γ/R?
A soap bubble has two spherical interfaces (inner and outer surface), each contributing 2γ/R.
What is capillary pressure?
The pressure difference across a curved meniscus in a capillary tube, governed by the Young-Laplace equation.