DrainageCalculators

About DrainageCalculators.com

Our Mission

DrainageCalculators.com provides free drainage and stormwater calculators to anyone who needs them -- homeowners, contractors, and engineers alike. Whether you are figuring out how to fix a wet yard, sizing a pipe for a client proposal, or modeling a detention pond for a commercial development, our tools deliver reliable results based on widely accepted engineering methods.

We believe that access to quality engineering tools should not be gated behind expensive software licenses or mandatory account sign-ups. Every calculator on this site is available immediately, at no cost, and with no registration required.

Is This Site For Me?

DrainageCalculators.com is built for three audiences. Here is how each one gets the most out of it:

Homeowners

You've got standing water in your yard, a wet basement, or you're planning a DIY drainage project. Our calculators help you figure out what you need -- pipe sizes, drain lengths, rain garden dimensions -- so you can fix it yourself or have an informed conversation with a contractor.

Contractors

You need quick field sizing for pipes, catch basins, and drainage systems. Our calculators give you professional-grade results you can use in bids and proposals, backed by the same engineering standards your competition uses.

Engineers & Designers

You need verified calculations with full methodology transparency. Every calculator shows the complete calculation breakdown with citations to FHWA, NRCS, ASCE, and other standards. Results are independently verified against published examples.

What You Get

DrainageCalculators.com gives you a comprehensive set of resources for drainage design and analysis:

  • 50+ free calculators covering hydrology, hydraulics, stormwater BMPs, and drainage structures -- from simple pipe sizing to detention pond routing.
  • 18 learning articles that explain the engineering methods behind the calculators, with worked examples and practical guidance.
  • Reference tables for Manning's n values, runoff coefficients, curve numbers, and other commonly needed design parameters.
  • Transparent calculations with KaTeX-rendered step-by-step breakdowns showing every equation, substitution, and intermediate result so you can verify the math yourself.

What Makes Us Different

  • No Login Required: Use any calculator instantly. We do not require an account, email address, or personal information.
  • Open Methodology: Every tool shows the equations it uses, the assumptions it makes, and the standards it references. Nothing is hidden behind a black box.
  • Verified Against Published Standards: Calculator results are checked against worked examples from FHWA, NRCS, ASCE, and other authoritative sources to ensure accuracy.
  • Engineering-Grade Methods: Our calculators implement established methods including the Rational Method, SCS Curve Number, Manning's equation, level pool routing, and more -- the same techniques used in professional practice and accepted by regulatory agencies.
  • Client-Side Processing: Calculations run entirely in your browser. Your project data stays on your device and is never sent to a server.
  • Free to Use: No subscriptions, no paywalls, no hidden costs. Every calculator is free, forever.

How to Get Started

Not sure where to begin? Here are two good starting points:

  • Browse the Calculator Index to find calculators organized by category -- Hydrology, Hydraulics, Stormwater BMPs, and Structures. Each calculator includes a description and guidance notes to help you choose the right tool.
  • Visit the Learning Center if you want to understand the engineering methods first. Our 18 articles cover topics from drainage design fundamentals to advanced hydrograph analysis, with clear explanations suitable for all experience levels.

If you already know what you need, jump straight to popular tools like the Rational Method, Manning's Pipe Flow, or French Drain Sizing calculators.

DrainageConnect.com

DrainageCalculators.com is a sister site to DrainageConnect.com , a supplier of drainage products including catch basins, trench drains, channel grates, pipe fittings, and related accessories. While the two sites complement each other, DrainageCalculators.com operates independently as a free resource -- you are never required to purchase anything to use our calculators.

In Short

  • Free forever -- no subscriptions, no paywalls, no hidden costs.
  • For everyone -- homeowners, contractors, and engineers.
  • Transparent -- every equation, assumption, and standard citation is documented.
  • Verified -- results checked against published engineering examples.
  • Private -- your data never leaves your browser.