Well Pump Flow Rate & GPM Calculator
Calculate your well pump's flow rate in gallons per minute (GPM) using either a bucket/container timed test or a drawdown recovery test.
Total gallons collected in the container during the test.
Number of seconds it took to fill the container.
Formulas Used
Method 1 — Volume / Time Test:
GPM = (Volume collected, gal) ÷ (Time, sec) × 60
Method 2 — Drawdown Recovery Test:
Drawdown (ft) = Pumping Level − Static Level
Casing Storage (gal/ft) = π × (D/2 ÷ 12)² × 7.48052
Volume Recovered (gal) = Drawdown × Casing Storage
GPM = Volume Recovered ÷ Recovery Time (min)
Where D = casing inner diameter in inches, and 7.48052 = gallons per cubic foot.
Assumptions & References
- Volume/Time method assumes a steady, consistent flow during the entire collection period.
- Drawdown method assumes the well casing is a uniform cylinder and that all recovered volume comes from within the casing (conservative estimate for low-yield wells).
- 1 cubic foot = 7.48052 US gallons (exact conversion).
- Residential minimum yield guidance based on the International Residential Code (IRC) and USDA Rural Development well standards (≥ 4 GPM preferred; ≥ 1 GPM with storage acceptable).
- Common residential casing diameters: 4 in (older/shallow), 5 in, 6 in (modern drilled wells).
- For accurate results, the pump should run until the water level stabilizes before recording the pumping level.
- This calculator does not account for aquifer transmissivity, specific capacity, or pump efficiency — consult a licensed well driller for detailed hydrogeological analysis.
- Reference: Driscoll, F.G. (1986). Groundwater and Wells, 2nd ed. Johnson Filtration Systems.