Weber Number Calculator

We = ρV²L / σ — ratio of inertial to surface tension forces. Determines whether droplets, bubbles, or free surfaces remain stable or break up.

Fluid Mechanics II

Common fluids — click to auto-fill density

Fluid density ρ (kg/m³)

Relative velocity V (m/s)

Characteristic length L (mm)

Typically droplet or bubble diameter, film thickness, or jet diameter.

Surface tension σ (N/m)

Weber number:

We = ρV²L / σ [dimensionless]

We = (dynamic pressure ρV²) / (capillary pressure σ/L)

Regime classification (liquid drops in gas):

We range	Behaviour
We < 1	Surface tension dominates — droplets spherical, interface stable
1 – 12	Competing forces — droplet deforms but may remain intact
12 – 100	Inertia dominates — bag breakup or stripping (critical We ≈ 12)
We > 100	Catastrophic atomisation — fine droplets, spray formation

Thresholds are indicative for liquid drops in air. Critical We varies with Ohnesorge number (Oh) and geometry.

Common surface tension values σ (N/m) at 20°C:

Applications:

Where:

Inputs