Well Volume Calculator
Enter the casing diameter, well depth and static water level and get the gallons standing in the well, gallons per foot, and the bleach for a chlorine concentration you choose.
Depth from the top of the casing down to the water.
Use the figure from your state or local health department's procedure.
Depths are measured from the top of the casing. The result updates as you type.
Water standing in the well
220.3 US gallons
150 ft of water × 1.469 gal per ft · 834 litres
| Gallons per foot of casing | 1.4688 gal/ft (18.24 L/m) |
| Water column | 150 ft |
What this page cannot tell you
How much water the surrounding rock or gravel pack holds, or what's in the pressure tank and plumbing — only the open casing column is counted. Chlorinating a well has its own procedure (unscented bleach, circulating, flushing, testing afterward); follow your health department's instructions, and treat the bleach figure only as the arithmetic for the concentration you enter.
How to calculate the water in a well
- Find the casing diameter. The inside diameter, commonly 4 or 6 in on drilled wells.
- Enter the well depth. Total depth from the top of the casing, from the well log or a measurement.
- Enter the static water level. Depth from the top of the casing down to the water when the pump hasn't run.
- Optional: a chlorine target. Enter the ppm from your health department's instructions and your bleach's strength.
10 situations where a well volume calculator helps
Shock chlorinating a well
The bleach amount depends on how much water is in the casing.
Purging before a water test
Sampling procedures often ask for a number of well volumes to be pumped first; know one volume in gallons.
Reading a well log
Turn depth and static level into stored water.
Comparing 4 in and 6 in casings
A 6 in casing holds 2.25 times as much per foot.
Drought checks
See how much the stored column shrinks as the static level falls.
Planning a pump replacement
Know the water you'll displace or pump out.
Treating a well with a product dosed per gallon
Get the gallons for the label rate.
Metric well data
Enter depths in metres; litres are shown.
Buying a property with a well
Understand the numbers on the well report.
Teaching groundwater basics
A worked cylinder-volume example with real units.
How the volume is worked out
The water standing in a well is a cylinder: the casing's cross-section times the height of the water column. Gallons per foot = π × (inside diameter ÷ 2)² × 12 ÷ 231, because a US gallon is 231 cubic inches (NIST Handbook 44). A 6 in casing holds 1.469 gallons per foot; a 4 in casing 0.653. The water column is the total depth minus the static water level.
Bleach: a concentration in ppm is milligrams of chlorine per litre of water. With bleach of P % available chlorine (treated as mass per volume, as labels state it), the bleach volume for C ppm is water gallons × C ÷ (P × 10,000). The target concentration and the procedure are yours to take from your state or local health department.
Limits: only the open casing column is counted — not water in the gravel pack or rock around the well, the pressure tank or the household plumbing, which a full disinfection also has to reach. Casing walls make the inside diameter slightly less than the nominal size. Everything runs in your browser.
Sources
- NIST Handbook 44 — US gallon = 231 cubic inches
Frequently asked questions
How many gallons per foot in a 6 inch well?
About 1.47 gallons per foot of water column.
How many gallons per foot in a 4 inch well?
About 0.65 gallons per foot.
How do I find the static water level?
From the well log, or by measuring down the casing with a well sounder or tape when the pump hasn't run for a while.
How much bleach to shock a well?
Enter the concentration your health department's procedure specifies and your bleach strength; the page does the arithmetic. It doesn't set a concentration.
Does this include the water in my pressure tank?
No — only the water standing in the casing.
Why does the casing size matter so much?
Volume grows with the square of the diameter, so doubling the diameter quadruples the gallons per foot.
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