Tubing Flow Calculator

Model tubing behavior using diameter, length, roughness, and fluid data. View losses, velocity, regime instantly. Export results and visualize system performance with confidence today.

Enter Tubing Inputs

Inner Diameter (mm)

Tube Length (m)

Flow Rate (L/min)

Fluid Density (kg/m³)

Dynamic Viscosity (cP)

Roughness (mm)

Minor Loss Coefficient, K

Elevation Change (m)

Inlet Pressure (kPa)

Example Data Table

Scenario	Diameter (mm)	Length (m)	Flow (L/min)	Density (kg/m³)	Viscosity (cP)	Roughness (mm)	K	Elevation (m)
Water Transfer Line	12.7	25	18	998	1.0	0.045	2.5	1.5
Light Oil Service	19.0	40	22	860	12.0	0.045	4.0	0.8
Coolant Return Loop	25.4	18	45	1030	2.8	0.020	3.2	-0.5

Formula Used

This calculator combines continuity, Reynolds number, a universal friction model, and Darcy-Weisbach pressure loss relations.

Cross-sectional area: A = πD² / 4
Velocity: V = Q / A
Reynolds number: Re = ρVD / μ
Churchill friction factor: a smooth all-regime equation using Reynolds number and relative roughness.
Major head loss: h_f = f(L/D)(V² / 2g)
Minor head loss: h_m = K(V² / 2g)
Total head: h_total = h_f + h_m + elevation
Pressure drop: ΔP = ρgh_total
Residence time: t = L / V

Use realistic density, viscosity, roughness, and fitting losses for trustworthy results.

How to Use This Calculator

Enter the tube inner diameter in millimeters.
Provide total straight length in meters.
Add the expected volumetric flow rate in liters per minute.
Enter fluid density and dynamic viscosity for your operating fluid.
Set tube roughness and total fitting loss coefficient, K.
Include elevation change if the outlet sits above or below the inlet.
Enter inlet pressure to estimate outlet pressure after losses.
Press the calculate button to view results above the form.
Use the graph for quick sensitivity checks around the chosen flow.
Download CSV or PDF files for records or documentation.

Frequently Asked Questions

1) What does this tubing flow calculator estimate?

It estimates velocity, Reynolds number, friction factor, head losses, pressure drop, mass flow, residence time, and outlet pressure from your tubing and fluid inputs.

2) Which viscosity value should I enter?

Enter dynamic viscosity in centipoise. If your source lists kinematic viscosity, convert it first using fluid density before using this calculator.

3) Why is roughness important?

Roughness affects wall friction. Higher roughness usually increases energy loss, especially in turbulent flow and longer tubing runs.

4) What is the minor loss coefficient, K?

K represents losses from fittings, bends, valves, tees, reducers, and entrances. Sum your component coefficients and enter the total.

5) Can I use this for gases?

You can use it for rough screening, but compressible gas systems may need additional density-change and pressure-coupled modeling for accurate design work.

6) What flow regime labels mean?

Laminar flow is usually below Reynolds 2300. Transitional sits between laminar and turbulent. Turbulent flow begins above about 4000.

7) Why might outlet pressure become negative?

That indicates the entered inlet pressure is lower than the calculated losses. Check the assumptions, units, or choose a stronger supply pressure.

8) Is this suitable for final engineering approval?

It is useful for planning, estimating, and comparing scenarios. Final approval should still consider detailed system geometry, temperature effects, and safety margins.