Private wells · storage
Well casing gallons per foot calculator.
Enter the inside diameter of your well casing to get gallons per foot, then add the well depth and static water level for the water stored in the casing. Runs in your browser; nothing is sent anywhere.
Planning aid: codes and soils vary by location. Confirm septic and well work with your local health department and a licensed professional.
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Worked example
A 6 inch casing: π × (0.25 ft)² = 0.1963 ft², and 0.1963 × 7.4805 = 1.469 gal per foot. For a 200 ft well with water at 50 ft, the water column is 150 ft, so about 150 × 1.469 = 220 gal is stored in the casing. A 4 inch casing holds 0.653 gal per foot.
Formulas, sources, and limits
Formulas: Gallons per foot = π × (diameter in feet / 2)² × 7.4805 gal per ft³. The 7.4805 comes from 1 US gal = 3.785412 × 10³ m³ and 1 ft = 0.3048 m exactly. Stored water = gallons per foot × (well depth − static water level).
Sources (retrieved 2026-10): NIST SP 811 Appendix B.8, conversion factors.
Limits: Geometry only. It uses the inside diameter, so a 6 inch nominal casing with a thick wall holds slightly less. It assumes casing runs the full depth. Use the pump-test yield, not casing storage, to judge whether a well meets demand.
Frequently asked questions
How many gallons per foot is a 6 inch well casing?
About 1.47 gallons per foot of water column.
How many gallons per foot is a 4 inch well casing?
About 0.65 gallons per foot.
How do I find the static water level?
It is the depth to water with the pump off, recorded in the driller’s log or measured with a well probe.
Why does this matter for shock chlorination?
The volume of water in the well sets how much bleach is needed; see the well shock chlorination calculator.