hydrocalculators.app

Hydraulic Calculators.

A free, accurate, single-purpose-tool collection for open channel flow, weir hydraulics, and pressurized pipe design — built for engineers, students, and consultants who need answers without a paywall.

Each tool here solves one problem well. No login, no rate limits. Calculations run entirely in your browser, so your project numbers never leave your machine. The math is verified against the standard references — Chow (1959), Henderson (1966), USBR, USGS — and every formula is shown openly so you can audit the result.

This site is a work in progress. Two calculators are live; the rest ship one per week. Bookmark and check back — or, better, dig into the live ones now.

Open channel flow
04 tools
live · ready to use
Manning's Equation
Compute discharge or normal depth in rectangular, trapezoidal, triangular, or circular channels. Includes Froude number, critical depth, and a 15-option roughness table.
Q = (1/n) · A · R^(2/3) · S^(1/2) →
coming soon
Critical Depth
Find the depth at which the Froude number equals one — the boundary between subcritical and supercritical flow. Closed-form for rectangular and triangular, iterative for trapezoidal and circular.
Q²·T / (g·A³) = 1 →
coming soon
Specific Energy & E-h Diagram
Plot the E-h curve for a given discharge and locate your flow on the subcritical or supercritical branch. Interactive teaching tool that replaces the static textbook figure.
E = h + Q² / (2g·A²) →
coming soon
Hydraulic Jump
Conjugate depths from the momentum equation. Returns sequent depth, energy loss, jump length, and jump type (undular through strong) with an SVG profile diagram.
h₂/h₁ = ½(√(1 + 8·Fr₁²) − 1) →
Weirs & spillways
04 tools
live · ready to use
Tyrolean (Bottom Intake) Weir
Drobir method for sloped trash-rack intake design. Sizes the rack length and bar geometry to capture a target discharge in mountain streams and small hydropower.
c = 0.6 · cos(β)^1.5 · (a/d) →
coming soon
Broad-Crested Weir
Discharge coefficient with corrections for approach velocity, weir height, and submergence. Workhorse calculation for irrigation, flood routing, and small hydropower.
Q = C_d · b · √(2g) · h^(3/2) →
coming soon
Sharp-Crested Weir
Three weir types in one tool: rectangular, V-notch (90°/60°/45°), and Cipoletti. The standard discharge measurement device for lab flumes and irrigation canals.
Q = (8/15) · C_d · tan(θ/2) · √(2g) · h^(5/2) →
coming soon
Spillway / Ogee Weir
USBR and Corps of Engineers ogee design. Discharge coefficient varies with operating-to-design head ratio, upstream face slope, and approach depth.
Q = C · L · H_e^(3/2) →
Pipes & structures
03 tools
coming soon
Pipe Friction Loss
Darcy-Weisbach with Colebrook-White or Swamee-Jain friction factors, plus Hazen-Williams as a quick check. For penstocks, water supply mains, and pumping systems.
h_f = f · (L/D) · v² / (2g) →
coming soon
Stilling Basin
USBR Type II, III, and IV energy dissipator design. Returns basin length, baffle dimensions, end-sill height, and required tailwater depth from spillway discharge and Froude number.
USBR Engineering Monograph 25 →
coming soon
Reservoir Routing
Modified Puls method for routing an inflow hydrograph through a detention pond or small reservoir. Outputs the outflow hydrograph with peak attenuation and lag time.
(2S/Δt + O) = I + (2S/Δt − O) →
Hydrology & water resources
01 tool
coming soon
Rainwater Harvesting & Tank Sizing
Estimate peak runoff from a rainfall event over a rooftop or paved catchment, then size a storage tank by simulating the cumulative water balance — inflow, outflow, and storage level — over the duration of the event.
V = C · A · P · ΔS = I − O →
About the project

Built by an engineer, for engineers.

Hydraulic engineering is full of calculations that should be free and instant — but somehow aren't. The reference textbooks cost hundreds of dollars, the proprietary software costs thousands, and the free calculators online are mostly outdated, cluttered, or wrong.

This site is the alternative: a small set of well-documented, mathematically verified, openly-formulated tools that work the way an engineering reference should. No login, no email capture, no upsells. Every formula is shown on the page; every assumption is stated. If you spot an error, the project welcomes corrections.

Calculations run entirely in your browser using JavaScript. Your input data — pipe diameters, flow rates, project numbers — never leaves your machine. There's no server-side processing, no database, no analytics on your inputs. The site is static HTML; you can save any calculator to your hard drive and run it offline.

— 01
Verified math
Every formula tested against worked examples from Chow, Henderson, USBR, and USGS references.
— 02
Both unit systems
SI metric and US customary on every calculator, with automatic conversion when you toggle.
— 03
Stays in your browser
No data leaves your device. The math runs client-side. Use it offline if you want.