Water & Hydraulics Calculators
Hydraulics calculators size pipe and channel flow, pump head, culverts, and drainage using standard civil engineering formulas — Manning's equation, Hazen-Williams, and basic flow-rate mechanics — for site drainage, irrigation, and water system planning.
Frequently asked questions
What is Manning's equation used for?
Manning's equation estimates flow through an open channel or a partially full pipe (a ditch, culvert, or storm drain) from the channel's shape, slope, and surface roughness. It's the standard formula civil engineers use for drainage and culvert sizing.
Why do flow-rate answers vary so much with pipe diameter?
Flow rate scales with cross-sectional area, which grows with the square of the diameter — doubling a pipe's diameter roughly quadruples its flow capacity at the same velocity. That's why upsizing a drain pipe even slightly makes a big capacity difference.
Are these calculators accurate enough for real drainage design?
They use the correct standard formulas for planning and sizing estimates. Real stormwater and culvert design also accounts for local rainfall intensity, upstream watershed area, and code-specified design storms — confirm final sizing with a civil engineer for anything beyond a homeowner drainage project.