Well Volume Calculator

Estimate the gallons (and liters) of standing water in a well from its casing diameter, total depth, and static water level, using the standard cylinder volume formula.

Quick Facts

Formula
V = π/4 × D² × H (cylinder volume)
H = total depth − static water level; cubic feet convert to gallons ×7.48052.
Capacity scales with diameter²
≈1.47 gal/ft for a 6" well
≈0.65 gal/ft for 4", ≈2.61 gal/ft for 8" — doubling diameter roughly quadruples capacity per foot.

Your Results

Calculated
Water volume
-
Gallons of standing water
Volume in liters
-
Metric equivalent
Water column height
-
Total depth minus static level
Capacity rate
-
Gallons held per foot of depth

Ready

Enter well diameter, total depth, and static water level, then press Calculate.

About the Well Volume Calculator

This calculator estimates how much water is standing in a well by modeling the well as a simple cylinder. Give it the casing diameter, the total depth of the well, and the static water level (how far down the water surface sits when the well is at rest), and it computes the volume of the water column in both gallons and liters.

The formula

The water in a well approximates a cylinder of water sitting inside the casing, so its volume follows the standard cylinder volume formula:

  • Water column height (H): total well depth minus static water level, both in feet.
  • Volume (cubic feet): V = π/4 × D² × H, where D is the casing diameter converted to feet (inches ÷ 12).
  • Volume (gallons): cubic feet × 7.48052 (the number of U.S. gallons in one cubic foot).
  • Volume (liters): gallons × 3.785411784.

Because the diameter term is squared, capacity grows much faster than depth: doubling the casing diameter roughly quadruples the gallons held per foot, while doubling the water column height only doubles the volume.

How to get the best results

  • Measure the casing diameter (or use the nominal size stamped on the well record — commonly 4", 5", 6", or 8").
  • Use the actual total depth of the well, not just the depth of the pump or screen.
  • Static water level should be measured after the well has rested (not actively pumping), since pumping temporarily lowers the water level (drawdown).

Practical context

This is a static volume — the water sitting in the casing at one moment — not a measure of how fast the aquifer can refill the well (its sustainable yield). It is commonly used for tasks like sizing a shock-chlorination dose or estimating in-well storage, but it does not replace a pump (drawdown) test for determining how many gallons per minute a well can sustainably deliver.

Frequently Asked Questions

What formula does this well volume calculator use?
It treats the well as a cylinder: volume = π/4 × D² × H, with diameter (D) and water column height (H) both in feet. The cubic-foot result converts to gallons by multiplying by 7.48052, and to liters by multiplying gallons by 3.785411784.
What is static water level and why does it matter?
Static water level is the depth from the ground surface down to the standing water surface when the well has not been pumped recently. Only the water column above the bottom of the well counts toward the stored volume, so the calculator subtracts static water level from total well depth to get that column height.
How much water does a 6-inch well hold per foot of depth?
About 1.47 gallons per foot, from π/4 × (0.5 ft)² × 7.48052. Because capacity scales with diameter squared, an 8-inch well holds about 2.61 gallons per foot and a 4-inch well holds about 0.65 gallons per foot.
Does this measure the well's sustainable yield?
No. This is the static volume of water sitting in the casing at the moment you measured static water level, not the rate at which the aquifer can recharge the well. Sustainable yield requires a pump (drawdown) test, not a volume calculation.

Related calculators