Engineering calculator reviewed for preliminary design use · Last updated: March 2026
Calculate Weber number We = ρv²L/σ. Apply to droplet breakup, bubble formation, and mist generation analysis. Use for spray nozzle design and gas-liquid contactor evaluation.
What this calculator is used for
The Weber number compares inertial forces to surface tension forces and is used
to assess droplet and bubble stability in multiphase systems.
Typical engineering use cases
Spray and atomization analysis
Gas-liquid contact equipment screening
Governing equation and methodology
We = ρ · v² · L / σ
Engineering assumptions and limitations
Representative characteristic length
Practical design notes
Weber number should be reviewed alongside Reynolds and Froude numbers to
understand interfacial behavior.
Worked Example
Given:
Water droplet (ρ = 998 kg/m³, σ = 0.072 N/m)
Relative velocity v = 10 m/s
Droplet diameter L = 1.0 mm (0.001 m)
Method: We = ρ·v²·L/σ = 998·10²·0.001/0.072.
Result: We ≈ 1390 — far above the ~12 critical value for droplet breakup.
Interpretation: Because We ≫ 12, aerodynamic forces overwhelm surface tension and the drop shatters into a fine spray. That is desirable in an atomizing nozzle but a problem in a separator, where you want We below ~12 to keep droplets intact and capturable — same number, opposite design intent.
Common Mistakes & Misuse
Using the pipe or nozzle diameter as the length scale when droplet breakup is governed by the droplet diameter — the two give very different We.
Comparing the result to a generic threshold without noting the critical We for the mechanism in question (≈12 for droplet breakup in a gas stream differs from jet or sheet criteria).
Holding surface tension σ constant when it falls markedly with temperature and with surfactants, which directly shifts We.
Treating a high We as the only requirement for fine atomisation while ignoring the Ohnesorge/viscosity effect that resists breakup.
Frequently Asked Questions
What does Weber number predict?
We = ρv²L/σ predicts whether a droplet or jet will remain intact or break up. High We (>12 for droplets) indicates breakup is likely. Low We means surface tension holds the droplet together.
How is Weber number used in spray design?
In spray nozzle design, We determines the droplet size distribution. Higher We at the nozzle exit produces finer droplets. It also affects spray penetration distance and evaporation rate.
For preliminary estimation and educational use only. Results may depend strongly on assumptions, input data, fluid or material properties, and the range of validity of the underlying equation. Verify critical calculations independently and follow the applicable code, specification, and formal engineering review process before using any result for design, procurement, fabrication, operation, or safety decisions.