Ideal for water, air, oils, and process streams. Supports pipes and ducts with smart area. Compare cases, save outputs, and document calculations confidently always.
| Case | Mass flow | Density | Geometry | Computed area (m²) | Velocity (m/s) |
|---|---|---|---|---|---|
| Water in 50 mm pipe | 0.50 kg/s | 998 kg/m³ | Circular, D = 0.05 m | 0.00196350 | 0.2552 |
| Air in duct | 0.20 kg/s | 1.20 kg/m³ | Rectangular, 0.20 m × 0.10 m | 0.02000000 | 8.3333 |
| Known flow area | 1.00 lb/min | 62.4 lb/ft³ | A = 0.01 ft² | 0.00092903 | 0.0081 |
These examples show how velocity changes with density and area.
This calculator uses the steady, one‑dimensional continuity relationship between mass flow rate, density, cross‑sectional area, and average velocity.
Average velocity helps you judge pressure losses, noise, erosion risk, and whether a pump, fan, or compressor is operating inside a reasonable range. Because velocity scales inversely with area, small diameter changes can significantly change results.
The calculator uses ṁ = ρ·A·v. If mass flow ṁ is fixed, increasing density or area reduces velocity. For constant density, doubling the area cuts velocity roughly in half.
Water near room temperature is about 998 kg/m³. Many mineral oils range from 830–900 kg/m³. Dry air at sea level is around 1.2 kg/m³. Density can change with temperature and pressure, so use site values when available.
For a circular pipe, area uses A = πD²/4. For a rectangular duct, area is A = w·h. If you already know flow area from drawings or a nozzle spec, choose “Known flow area” and enter A directly.
Area grows with the square of diameter. A move from 50 mm to 75 mm increases area by (75/50)² = 2.25, so velocity drops to about 44% for the same mass flow and density.
Many water lines are designed around 0.5–3 m/s to balance size and losses. Air ducts often target about 2–8 m/s depending on noise limits. Slurries may require higher speeds to avoid settling, but material wear can increase.
When enabled, Reynolds number uses hydraulic diameter. For internal flows, Re < 2300 is often treated as laminar, 2300–4000 transitional, and Re > 4000 turbulent. These cutoffs are rules of thumb, not guarantees.
Use consistent operating conditions: density and viscosity should match the same temperature and pressure. If your “area” is a rough estimate, expect velocity uncertainty. For ducts, measure clear internal dimensions, not external sizes. Save exports to document assumptions and units.
Not from mass flow alone. Density links mass flow to volumetric flow, so it is required for velocity when using v = ṁ/(ρA).
This tool assumes the cross section is fully flowing. For partially full flow, compute the wetted area for that level and use the “Known flow area” option.
Use dynamic viscosity (μ) if you have it in Pa·s, mPa·s, or cP. Use kinematic viscosity (ν) if you have it in m²/s or cSt.
Because area depends on diameter squared. Small diameter changes create large area changes, which strongly affect velocity for the same mass flow.
No. It uses average density as an input. For high-speed or high-pressure gas flows, density may vary along the line and a compressible model is needed.
Split the total mass flow among parallel branches, then run each branch using its own diameter and density. Equal pipes usually share flow roughly evenly.
It is an equivalent diameter for non-circular passages. For a rectangle, Dh = 2wh/(w+h). It is used for Reynolds number and friction correlations.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.