Pipe Diameter — Companion Article
1. What this tool does
Pipe Diameter finds an inside diameter from continuity, Q = V × A. The user enters a flow in m³/h, L/s, or US gpm, and a velocity range. The minimum inside diameter uses the top of the range. The inside diameter at the bottom of the range is shown as well. Optional density reports mass flow only and is not used in the diameter.
2. When to use it
Use it when a designer has a flow and a velocity and wants the bore that goes with them. The result is preliminary. A velocity is not a line specification.
3. Inputs
Enter the flow and the velocity, or start from a preset and type over it.
Enter a density only if mass flow is wanted. It does not change the diameter.
Service presets, which the user can type over, are named on the page:
- Water: Engineering Toolbox, 0.9–2.4 m/s for water in steel pipe at low pressure. Not a code limit.
- Light oil: Carl Branan, Rules of Thumb for Chemical Engineers, clean single-phase liquids, 1.5–4.0 m/s. A starting range, not an oil-grade table.
- Viscous oil: no range is stored.
- Steam: Engineering Toolbox, saturated steam at 0–30 psi, 20–30 m/s. Other steam conditions differ.
- Gas: Branan, clean single-phase gas, 15–40 m/s. Not a code limit.
4. How it works
The running tool is the calculation. The continuity relation is Q = V × A, as the page states. The minimum inside diameter uses the top of the velocity range. The inside diameter at the bottom of the range is shown as well.
Optional density reports mass flow only. It is not used in the diameter.
A nearest nominal size is behind Settings, PD Pipe Diameter, and defaults to off. Turning it on still shows nothing unless another integration passes inside-diameter rows through the pd_dia10_nominal_rows filter. This tool does not contain a B36.10 table. Until a list is supplied, the page says to enter the selected nominal size.
5. Understanding the result
Read the minimum inside diameter. If a range was entered, also read the inside diameter at the bottom of the range.
The stored ranges are starting points. The worked case in section 7 used a single velocity. It did not use the stored water range.
6. Engineering considerations
The preset citations are Engineering Toolbox and Carl Branan, Rules of Thumb for Chemical Engineers, as printed on the page. They are not code limits. Viscous oil has no stored range.
No catalogue facts are read. No nominal-size table is shipped.
The page does not name a piping code edition. This article does not add one.
7. Example
Entered on the live page on 3 October 2026: water, flow 100 m³/h, velocity 2 m/s. The figures were hand-checked.
- Q = 0.0277778 m³/s
- Minimum inside diameter = 132.981 mm
This run used 2 m/s. It did not use the stored water range 0.9–2.4 m/s. That range is a preset on the page and is not a code limit.
8. Standards/references (licensed vs interim)
No catalogue facts are read. The continuity relation is Q = V × A, as the page states. The preset citations are Engineering Toolbox and Carl Branan, Rules of Thumb for Chemical Engineers, as printed on the page. This article does not name a piping code edition. The page does not name one.
Interim pipe dimensions on this site follow ASME B36.10-2022 Table 2-1. This tool does not use that table.
9. Limitations/disclaimer
- The result is preliminary and needs engineering review. A velocity is not a line specification.
- The stored ranges are starting points. Viscous oil has no stored range.
- Density does not change the diameter.
- No nominal-size table is shipped.
A member check is not an engineering fact.
10. Use the tool
Calculate now: Pipe Diameter
Related tools
Line Sizing, at /tools-training/line-sizing/, calls the Engineering API for catalogue entities. This page does not. It is a separate calculator.