Plumbing & Fluid
Pipe Diameter Calculator
Use continuity to solve the inside diameter, volumetric flow or mean flow velocity of a full circular pipe. Compare units directly and keep calculated bore separate from nominal pipe size.
Change any input to update the calculation. Unit changes preserve the physical quantity.
Inputs
Calculated locally in your browser. No sign-up or input upload.
Results
Calculated inside diameter
41.203 mm1.622 inVolumetric flow
2 L/s120 L/min7.2 m³/h0.002 m³/s31.701 GPM (US)4.238 CFMMean velocity
1.5 m/s4.921 ft/sAssumptions & checks
Calculated diameter is inside bore, not nominal size. Continuity does not check pressure loss, roughness, fluid properties, partial filling, compressibility or pipe-code compliance.
Formula
Full circular cross-section, with mean velocity through the same section.
Worked example
Using the default values shown in the calculator, the same formula gives the following result. This is a quick sanity check for the calculation, not a design recommendation.
Inputs
- Volumetric flow
- 2 L/s
- Mean flow velocity
- 1.5 m/s
Result
- Calculated inside diameter
- 41.203 mm
- Volumetric flow
- 2 L/s
- Mean velocity
- 1.5 m/s
Related calculators
Continue your workflow with a related calculation.
Plumbing & Fluid
Drainage Slope Calculator
Calculate drainage slope, fall, run or ending elevation. Compare percent, 1:X, mm/m, cm/m, in/ft and degrees with a run-and-fall diagram.
Electrical
Voltage Drop Calculator
Estimate DC or AC resistive voltage drop, minimum conductor size or maximum cable length with copper/aluminum, AWG/mm² and conductor temperature.
Freight & Logistics
Multiple-Carton CBM Calculator
Add mixed-size carton rows to calculate CBM per carton and row, total m³ and ft³, carton count, shipment weight and density with mixed units.
Plumbing & Fluid
Hazen-Williams Calculator
Solve water-pipe friction head loss, pressure loss, flow or inside diameter using Hazen-Williams with editable C-factor and metric or imperial units.
Plumbing & Fluid
Pump TDH Calculator
Estimate pump total dynamic head, pipe and fitting losses, pressure head and hydraulic power with editable fluid properties and metric or imperial units.
Technical references for this calculation
Frequently asked questions
Can I order a pipe by this diameter?
Use the result to compare actual inside diameters in the manufacturer's pipe schedule. Nominal size and outside diameter do not identify the bore by themselves.
Does CFM make this a duct sizing calculation?
CFM is an available volumetric-flow unit. The model still assumes a full circular section and does not select velocity criteria or calculate pressure loss.