Math Reference

Water Operator Math Formulas & Calculators

Every formula on the exam, explained with worked examples and live calculators. From someone who's used them in the field.

Pounds Formula
The most important formula on the exam. Lbs/day = mg/L × MGD × 8.34, all three rearrangements, worked examples, and a live calculator.
Learn the pounds formula →
Flow Rate Calculations
MGD, GPM, and CFS conversions plus Q = A × V for pipes and channels. Includes a unit conversion calculator.
Learn flow rate math →
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Detention Time
Tank volume, hydraulic retention time (HRT), and why getting the detention time right matters for sedimentation and disinfection.
Learn detention time →
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Dosage & Chlorine
Dose, demand, residual, and feed rate. CT values, product strengths, and how to calculate actual chemical usage.
Learn dosage calculations →
Formulas Cheat Sheet
All essential formulas on one page. Quick reference with variables, worked examples, and conversion factors. Print or save for exam prep.
Open cheat sheet →
Quick Reference

Key Conversions

Memorize these. They show up everywhere on the exam and in real plant operations.

To Convert Multiply By
MGD to GPM× 694.4
GPM to MGD× 0.00144
CFS to GPM× 448.8
Gallons to cubic feet÷ 7.48
Cubic feet to gallons× 7.48
MG to gallons× 1,000,000
Weight of water8.34 lbs/gallon
1 mg/L =1 ppm

Need Help with Math? Ask Randy.

Randy can walk you through any formula step by step, generate practice problems, and explain where each number comes from. Ask him about the pounds formula, unit conversions, or any exam math topic.

Heather Heltzinger
Licensed Class C Water & Wastewater Operator | Founder, Renaissance Labs LLC

23+ years of experience in SCADA systems and treatment plant management. CO-100 Top 100 Small Business winner. Built RandyAI to give operators the study tools she wished she had.