Professional Drainage Sizing — Fast and Accurate
Quick field sizing tools backed by NRCS, FHWA, and ASCE standards. Get accurate pipe sizes, drain capacities, and pond volumes you can use in bids and proposals.
Most-Used Contractor Tools
The calculators contractors reach for most often. All include shareable URLs and unit toggling.
Rational Method Calculator
Calculate peak stormwater discharge using the Rational Method (Q = CiA).
Open CalculatorManning's Equation for Pipe Flow Calculator
Calculate pipe flow discharge, velocity, and hydraulic properties using Manning's equation.
Open CalculatorFrench Drain Calculator
Calculate French drain capacity, pipe sizing, and storage volume.
Open CalculatorCatch Basin Calculator
Calculate catch basin sizing, outlet pipe capacity, and sediment storage volume.
Open CalculatorTrench Drain Calculator
Calculate trench drain capacity using Manning's equation.
Open CalculatorVegetated Swale Calculator
Calculate vegetated swale hydraulics including normal depth, velocity, and capacity using Manning's equation with variable roughness based on vegetation retardance.
Open CalculatorPond Sizing Calculator
Calculate preliminary detention pond storage requirements using the Modified Rational Method.
Open CalculatorDownspout Sizing Calculator
Calculate required downspout size based on roof area and rainfall intensity.
Open CalculatorManning's Channel Calculator
Calculate open channel flow using Manning's equation.
Open CalculatorInlet Interception Calculator
Calculate inlet interception efficiency for roadway drainage using HEC-22 methodology.
Open CalculatorBuilt for the Field
Shareable URLs
Every calculation generates a URL you can share with clients or include in proposals.
Unit Toggle
Switch between imperial and metric units with one click. Results update instantly.
Standard Methods
Every calculator uses published methods from NRCS, FHWA, ASCE, and other authorities.
Reference Tables
Quick access to Manning's n, pipe sizes, runoff coefficients, and soil properties.
Quick Reference Tables
The values you look up most often, all in one place.
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