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 plugin 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. They were not re-run for this remap.
- 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.
This draft does not class those citations as licensed standards data or as interim owner-authorised data. The interim pattern in the owner decisions log is ASME B36.10-2022 Table 2-1. This tool does not use that table. Owner engineering review confirms the source classification before publish.
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. The note is under Repository notes.
10. Use the tool
Calculate now: Pipe Diameter
Shortcode: Preliminary. This result needs engineering review before anyone uses it. A velocity range is a starting point, not a line specification. Line Sizing on this site calls the Engineering API for catalogue entities. This page does not. It is a separate calculator: inside diameter from continuity. Q = V × A A = π × d² / 4 d = sqrt(4 × Q / (π × V)) Q is the volume flow you enter. V is a velocity you accept. d is the inside diameter. The minimum inside diameter uses the top of the velocity range, because a higher velocity gives a smaller bore. The inside diameter at the bottom of the range is shown as well. Density, if you enter it, is used only to report mass flow. It does not change the diameter. 1 L = 0.001 m³. A flow in m³/h is divided by 3600. 1 US gallon = 231 in³ = 231 × (0.0254 m)³, and US gpm is that volume divided by 60. 1 ft = 0.3048 m. Water: Engineering Toolbox, water in steel pipe, 0.9–2.4 m/s (180–480 ft/min), low pressure up to 50 psi (3.5 bar), about 10–38°C. Not a code limit. https://www.engineeringtoolbox.com/fluid-velocities-pipes-d_1885.html Light oil: Carl Branan, Rules of Thumb for Chemical Engineers, the published starting range for clean single-phase liquids, 1.5–4.0 m/s. This is that starting range. It is not an oil-grade table. Viscous oil: no velocity range is stored. Enter the range you accept. Steam: Engineering Toolbox, saturated steam at 0–30 psi, 20–30 m/s (4000–6000 ft/min) in steel pipe. Other steam conditions differ. Not a code limit. https://www.engineeringtoolbox.com/flow-velocity-steam-pipes-d_386.html Gas: Carl Branan, Rules of Thumb for Chemical Engineers, the published starting range for clean single-phase gas, 15–40 m/s. Not a code limit. Choosing a service fills the velocity boxes. You can type over them. Changing the velocity unit does not convert the numbers. Nominal size is not suggested unless a bore list is supplied, and that list is off by default. This page does not contain a B36.10 table. Numbers on the result line are rounded for display with six significant figures. Enter your selected nominal size to compare. Pipe Diameter version 1.0.0 This records your check of the tool output. It does not change the tool or the engineering data. . Version 1.0.0. Re-check this article when the tool version changes.Pipe diameter
Formula
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How this calculation works: companion path TBD.
That return link is not on the tool page. This draft does not add it. The public article path is TBD because this file is not published.
The article stays public if the tool is restricted. A visitor with no entitlement sees a lock message on the tool, not a bare “Access denied”. The copy is in the Companion Article standard. This draft does not place that lock on the page and does not mark the tool free, Pro, or Enterprise.
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.