The Pipe Sizing tool automatically resizes pipe segments according to the flow each one carries. It applies the sizing criteria and constraints you choose. Run it after you've confirmed connectivity and flow totals with the System Browser and System Inspector.
Workflow
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Before You Start
The system must be fully connected. Sizing depends on correct flow in every segment, and disconnected pipes, fixtures, or equipment give wrong results. Clean these up first with the System Browser and System Inspector.
Flow values must be set at the sources and loads.
For hydronic systems, set the design flow (GPM) on coils, terminal units, and equipment connectors.
For plumbing systems, make sure fixtures have their fixture unit values. Revit converts fixture units to flow, accounting for diversity.
Check that calculations are enabled. In the piping system type properties, the Calculations parameter should be set to All, or at least Flow Only.
Review the available sizes. Go to Manage tab → MEP Settings → Mechanical Settings → Pipe Settings → Segments and Sizes. For each pipe segment (material and schedule) your pipe types use, confirm that the sizes you want are checked as Used in Sizing. The tool only picks from those sizes.
Check your calculation settings. Under Pipe Settings → Calculation, review the methods used for pressure drop and for flow conversion from fixture units. These affect your results.
Know which systems suit this tool. It works best for pressurized systems: hydronic supply and return, domestic hot and cold water, and fire protection. Gravity systems such as sanitary and vent depend on fixture units and slope. Check that their results follow the sizing tables in your applicable plumbing code.
Work on a copy, or save first. Sizing changes many elements at once. Undo works, but a saved fallback is safer.
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Using the Duct/Pipe Sizing Tool
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Selecting the Piping to Size
Hover over a pipe in the run you want to size.
Press Tab until the whole run or system highlights, then click to select it.
To size only part of a system, select just those segments and fittings. Use Ctrl to add elements to the selection.
If your selection includes other categories, use Filter to keep only pipes and pipe fittings.
On the contextual tab, click Duct/Pipe Sizing in the Analysis panel.
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Choosing the Sizing Criteria
In the Pipe Sizing dialog, set how sizes are calculated:
Friction: sizes pipes to a target pressure drop, such as 4 ft of head per 100 ft.
Velocity: sizes pipes to a target maximum velocity, such as 4 FPS for domestic water. This helps limit noise and erosion.
Combining the two:
Only: uses a single criterion.
And: the pipe must satisfy both criteria. This gives more conservative, larger pipes.
Or: the pipe must satisfy at least one criterion.
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Setting Constraints
Branch Sizing controls how branch pipes relate to the fixtures and equipment they connect to:
Calculated Size Only: sizes branches purely from flow.
Match Connector Size: keeps branches at the fixture's or equipment's connector size.
Larger of Connector and Calculated: uses whichever is bigger. This is a common safe choice, because it avoids undersizing fixture connections.
Pipes are round, so there are no height or width restrictions. The size options come entirely from the sizes enabled for the pipe segment.
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Running the Tool
Click OK. Revit resizes the selected pipes and updates the connecting fittings to match.
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Reviewing the Results
Re-run the System Inspector. Confirm that pressure losses along the critical path are reasonable for pump sizing and that no segment has an unexpectedly high loss.
Check for coordination problems. Larger pipes may now clash with structure, ductwork, or other services.
Look for awkward transitions. Sizing can create many small size changes along a run. Consolidate them where a simpler, constant size is more practical to install.
Spot-check segment sizes. Select individual pipes and verify their size, flow, and velocity in Properties.
Verify code minimums. Make sure plumbing branch and fixture connection sizes meet the minimums in your applicable code.
Fix any failed connections. Occasionally a fitting can't adapt to new sizes and the connection breaks. Reconnect it and re-check the system.
Recommended Workflow
Confirm connectivity and flow totals with the System Browser and System Inspector.
Verify the flow and fixture unit values, the calculations setting, and the sizes enabled for each pipe segment.
Select the pipe run or system using Tab, filtering if needed.
Open Duct/Pipe Sizing, then choose criteria and constraints.
Run the tool.
Re-inspect with the System Inspector and check for clashes, awkward transitions, code minimums, and broken connections.
Make manual adjustments, then re-run sizing on specific runs if needed.