Stormwater Pipe Sizing
Size a stormwater pipe in minutes, with the AEP, runoff coefficient, and rainfall already handled for you.
The Quick Stormwater Calculator is the everyday tool for single-pipe stormwater sizing. Pick the catchment type, drop in the area, and let Clarus pull the right design AEP, the recommended runoff coefficient, and the rainfall intensity for your site. Get a sized pipe with the standards basis stamped on the result.
Sizing paths
Uses the Rational Method end-to-end. Choose a catchment preset, review or edit its runoff coefficient and supported design basis, then enter the contributing area and rainfall intensity. Mixed catchments calculate their weighted coefficient from editable component areas and coefficients.
For a design flow already established by a stormwater model or upstream calculation, leave Catchment unconfigured and enter Additional flow directly. When both are supplied, Clarus adds the contributions before pipe sizing.
Built in
When a catchment is part roof, part paving, part landscaping, the weighted components builder lets you split it by area. Clarus computes the area-weighted runoff coefficient automatically, no manual averaging.
Enter the design intensity manually, or use address lookup: type the site address and Clarus pulls the IFD rainfall intensity for the selected design basis and five-minute duration, stamping the source URL into the result. The selected address routes to the supported AU or NZ provider.
Enter as a ratio (1:100), a percent (1%), or slope in m/m. Clarus normalises to the form the hydraulics need and shows the others for clarity.
Catalogues
Bread-and-butter sizing using standard PVC stormwater dimensions.
The manufacturer's catalogue dimensions and roughness for projects specifying that product.
The supplied Class 2 concrete pipe internal diameters with the established concrete roughness.
Results
Every Quick Stormwater result is complete and auditable.
With the runoff coefficient used and its source label, so reviewers can see how the flow was derived.
From the Colebrook-White solution at your slope. The unrounded number that tells you whether you're sized at the edge of the catalogue or with room to spare.
A real catalogue DN with internal diameter, velocity at design flow, and hydraulic capacity status at the entered slope.
Every size in the chosen catalogue with capacity, velocity, and hydraulic status. The recommended size is flagged; the rows around it show what happens going up or down.
Shows the catchment-derived contribution and additional flow separately, then the combined flow used for pipe sizing.
The assumptions that fed the design flow: AEP, runoff coefficient basis, rainfall provider, intensity, and catchment breakdown.
Codes and messages for anything that needs attention before issue, from hydraulic failure to missing rainfall or an unresolved address.
Every snapshot shows exactly which catchment defaults, pipe catalogue version, and rainfall source the calculation used. The PDF carries the same stamps.
Why it's worth using
Box gutters are 1% AEP, eaves gutters are 5% AEP, mixed catchments resolve from the receiving system. Clarus encodes these so you don't have to remember which catchment type goes with which design event, and the reviewer sees the rule that was applied.
Twelve catchment types each carry a recommended coefficient with its basis labelled. Mixed catchments are area-weighted automatically, and the result stamps the coefficient and label so the report explains itself.
Type the site address, get the rainfall intensity for the design AEP and duration in seconds. The source URL is stamped on the result and goes into your PDF so reviewers can verify.
Use catchment runoff, an additional flow supplied by a stormwater modeller, or both together in the same additive workflow. No mode switching.
Clarus shows you the catalogue around the answer with capacity, velocity, and hydraulic status per row. The "could we drop one size?" question is answered on screen.
Australia and New Zealand rainfall providers are selected from the resolved address. There is no country setting in the calculation and no silent Australia default.
Generic PVC, Vinidex StormPRO SN8, and RCP rubber ring jointed Class 2 use their established internal diameters and roughness so velocity and capacity numbers match the selected catalogue.
Save calculations as snapshots, attach them to a project, and export PDF reports stamped with the AEP, runoff coefficient, rainfall source, and pipe catalogue version. The issued document is auditable end to end.
When it grows
Single-pipe stormwater sizing for residential, commercial, and light infrastructure. When the design needs a full network, the same project record carries forward into Schematic Studio, where every branch is sized automatically as you sketch, with the same standards-aligned outputs behind every run.
Spin up a free trial and size your first pipe in minutes, with the AEP, runoff coefficient and rainfall handled for you, and a stamped, auditable PDF you can defend in review.
Start your first stormwater pipe sizing calculation