Well Water Flow Rate, Peak Demand & Pressure Tank Calculator

Residential Water Systems: Well Yields & Pressure Tank Sizing

• The 5-Gallon Bucket Test: The industry-standard DIY flow test: turn on an unrestricted spigot near the pressure tank and time how many seconds it takes to fill a clean 5-gallon bucket).

• The 1-Minute Minimum Pump Cycle Rule: Submersible well pump electric motors generate heat on startup. Sizing a pressure tank to ensure at least 60 seconds of continuous run time per cycle protects the pump motor windings from burning out prematurely.

How to Use This Calculator

Enter your Flow Rate Measurement Method — choose from 5-Gallon Bucket Test (Enter Container Volume & Fill Seconds), Direct GPM Well Test Flow Rate (from Well Driller Log), Test Bucket / Container Volume (Gallons) (e.g. 5 (5.0 gallon bucket)), Time to Fill Bucket Completely (Seconds) (e.g. 30 (30 seconds to fill 5 gallons = 10 GPM)), Known Well Flow Rate (GPM [if direct]) (e.g. 10 (10 GPM)), Number of Bathrooms in House — choose from 1 Bathroom (Peak Demand: ~6 to 8 GPM), 2 to 2.5 Bathrooms (Peak Demand: ~10 to 12 GPM), 3 to 4 Bathrooms (Peak Demand: ~14 to 18 GPM), and Pressure Switch Setting (PSI Cut-in / Cut-out) — choose from 30 / 50 PSI (Drawdown factor ~31%), 40 / 60 PSI Standard (Drawdown factor ~27%), 50 / 70 PSI High Pressure (Drawdown factor ~23%). Results update instantly as you type — adjust any value to compare scenarios.

The Formula

Well Hydraulics \& Pressure Tank equations:

Well Flow Rate (GPM) = ((Bucket Volume (Gallons)) / (Fill Time (Seconds))) × 60

Required Usable Drawdown = Pump Flow Rate (GPM) × 1.0 Minute Min Runtime

Total Pressure Tank Volume = (Required Usable Drawdown) / (Drawdown Factor (≈ 0.27 for 40/60 PSI))

Drawdown Factor: D_f = 1 - (Cut-in Absolute Pressure (PSIA)) / (Cut-out Absolute Pressure (PSIA))

Worked Example

For example, performing a 5.0 gallon bucket test at an outdoor hose bib where the bucket fills in 30.0 seconds for a 2.5 bathroom home (11.0 GPM peak demand) on a Well Flow Rate is \. Minimum usable drawdown is 10.0 gallons. Recommended pressure bladder tank size is \ (e.g. standard 44-gallon tank).

Understanding Your Result

Health calculations provide population-average estimates based on validated formulas. Individual variation exists — your actual physiology may differ from the calculated baseline. Compare your result to the relevant clinical reference range (WHO, CDC, NIH, or specialty guidelines). For values outside normal ranges or for clinical decisions, consult a qualified healthcare provider. A single measurement is less meaningful than a trend over time under consistent measurement conditions.