When is it useful?
Weber number compares fluid inertia with surface tension. It is useful for droplets, bubbles, sprays, and other flows where a fluid interface affects shape or breakup.
Formula and inputs
Enter density ρ in kg/m³, representative speed v in m/s, characteristic length L in m, and interfacial tension σ in N/m. Because speed is squared, doubling v multiplies We by four if the other inputs stay fixed.
Open this calculatorWorked example
For ρ = 1000 kg/m³, v = 2 m/s, L = 0.01 m, and σ = 0.072 N/m, We = 1000 × 2² × 0.01 ÷ 0.072 ≈ 555.56.
Interpreting the result
For this example and length scale, inertia is large relative to surface tension. The ratio alone does not establish a universal droplet-breakup threshold.
Limits and cautions
Choose σ for the relevant pair of fluids and temperature. A droplet diameter and a nozzle diameter define different Weber numbers; state which one you used.
Formula and concept reference: NASA — Dimensionless Numbers, Weber Number. We created the sample inputs and calculations for this guide.