Culvert / Outlet Sizing – Orifice, Weir & Manning

Quick‑check sizing and capacity calculator for culvert outlets and basin control structures.
Modes: orifice (circular), sharp‑crested weir (rectangular) and full‑flow circular Manning culvert.

1. Settings & Mode Units & Formula

Choose unit system and sizing mode. Then enter the required inputs for that formula. Use routed peak flow from the reservoir tool as your design discharge.
Gravity g is taken as 9.81 m/s² (SI) or 32.2 ft/s² (US).
Change the mode here; inputs below will update automatically.
Outlet sizing Detention basin design Culvert capacity