Well Volume Calculator - Casing, Depth & Capacity

A well volume calculator is a water-storage tool that finds the amount of water held in a residential or farm well from the inside diameter of the well casing and the depth of the standing water. Enter the casing diameter and the static water depth, and the calculator returns the total water in US gallons, liters, and cubic feet, plus a per-foot capacity figure.

• • Size Backup Storage for a Domestic Well: Estimate how many gallons a 4, 6, or 8 inch casing actually holds at the static water level, so you can size a pressure tank or emergency storage.
• • Plan a Well Drawdown Test: Use the per-foot or per-meter capacity to convert a measured drawdown into the gallons the well can deliver between pump cycles.
• • Compare Drilled and Dug Wells on the Same Property: Switch between a drilled 6 inch cased well and a 3 foot wide dug well to see how casing diameter changes total storage.
• • Convert Field Measurements for Permits and Reports: Translate a driller's log in inches and feet into the liters and cubic feet a water-use permit or a household water budget often requires.

The math behind a well is the same cylinder formula used for any vertical tank, so once the casing diameter and the static water depth are known, the storage volume is determined by pi times the radius squared times the water column height. The calculator handles the unit conversion in both directions.

For water budgeting across a whole household, our water usage calculator turns daily consumption into monthly and annual water costs.

The well volume calculator treats the well as a right circular cylinder. The inside radius of the casing becomes the radius of that cylinder, and the static water depth becomes the cylinder's height. The result is the well's storage volume in cubic feet, which is then converted to US gallons and liters.

• r: The inside radius of the well casing or borehole, equal to half the casing inside diameter.
• h: The vertical height of the standing water, measured from the static water level down to the bottom of the pump intake or well screen.
• V: The raw volume of the well in cubic feet, computed before any unit conversion.

When the form is set to metric, the calculator converts the casing diameter from centimeters to feet and the water depth from meters to feet internally, runs the same cylinder formula, and then expresses the result in liters and the imperial volumes. The conversion constants come from the National Institute of Standards and Technology.

According to Wolfram MathWorld, the volume of a right circular cylinder is V = pi * r^2 * h, where r is the radius of the base and h is the height, which is the geometric basis for the well volume formula used here for a cased well or any vertical tank of the same shape.

For a more general treatment of cylinder volume that lets you choose between radius, diameter, or circumference as the input, our cylinder volume calculator runs the same formula in a fully unit-agnostic way.

Four short concepts cover every measurement you need to size the water in a well.

Most homeowners confuse the drilled depth of the well with the static water depth, and most conflate a flow test result with a storage number. The four concepts above let you keep those ideas separate when you read a driller's report. For the open-air analog of a cased well, the pond calculator applies the same cylinder formula to give the same gallon and liter totals.

Use the well volume calculator in five short steps to size the water in a residential or farm well.

1. 1 Pick the Unit System: Choose imperial (inches and feet) for US driller's reports or metric (centimeters and meters) for international reports.
2. 2 Enter the Casing Inside Diameter: Type the interior diameter of the well casing. Most drilled domestic wells are 4 or 6 inches; 6 inch casing is the most common residential size.
3. 3 Enter the Static Water Depth: Type the depth of the water column from the static water level down to the bottom of the pump intake or well screen, in feet or meters.
4. 4 Select the Well Type: Choose drilled cased well for a steel-cased or PVC-cased borehole, or dug or bored well for a wider hand-dug well on older properties.
5. 5 Read the Storage Reading: Read the total water in US gallons, liters, and cubic feet, then reuse the per-foot capacity for the same casing at any other water depth.

A 6 inch cased well reads 100 ft of static water. Enter 6 for the casing diameter, 100 for the water depth, and leave imperial selected. The calculator reports 146.88 US gal, 556 L, and 19.63 ft^3, and a per-foot capacity of 1.47 gal/ft.

To size a 24 hour emergency reserve for a household that uses 300 gal per day, multiply 1.47 by 204 ft of water depth to get the same 300 gal from the well itself, and use the rainwater harvesting calculator to add roof-collected water to that reserve.

A well volume calculator turns a driller's report into a usable storage number without manual conversion.

• • Three Storage Units in One Read: Get the same well in US gallons, liters, and cubic feet at the same time, so you can match the unit the rest of your water plan uses.
• • Imperial and Metric Without Re-typing: Switch between inches and feet and centimeters and meters on the same form, and let the calculator handle the conversion in both directions.
• • Reusable Per-Foot Capacity: Use the per-foot or per-meter capacity as a property of the casing itself, so the same casing returns a usable reading for any other water depth.
• • Drilled and Dug Wells on One Form: Toggle between a 4, 6, or 8 inch drilled cased well and a wider hand-dug well to compare storage on the same property.
• • Cuts Manual Math Errors: The cylinder formula and the gallon, liter, and cubic-foot conversion factors are easy to mix up. The calculator handles them automatically and rounds to two decimals.

For property owners who already have a pressure tank or cistern downstream of the well, the same per-foot or per-meter figure can be reused to size a backup reserve without re-measuring the casing.

To convert the per-foot figure into a drawdown in gallons per minute, the gallons to cubic feet calculator runs the same conversion in reverse.

Four practical factors control the precision of a well volume result, and two limits apply to any driller's log or hand measurement.

• • The calculator assumes a straight-walled casing. Real wells can be slightly out of round, ovaled by drilling, or constricted by biofouling, so the true volume is a little lower.
• • The calculator measures only the volume held in the casing, not the long-term yield of the well. A separate well yield test is required for the flow side.

These factors and limits are the practical concerns for a residential or farm well volume reading. Casing age, mineral scaling, and biofilm on the inside of the screen can each shave a few percent off the theoretical volume, so the reading is best treated as a measured upper bound.

According to National Institute of Standards and Technology (NIST), one US gallon equals 3.785411784 liters and one cubic foot equals 28.316846592 liters, which is how this calculator converts the well raw cubic-foot volume into US gallons and liters.

For the construction side of a new well, the tank volume calculator and the pond calculator run the same cylinder math on rectangular and circular tanks and ponds, and the cylinder volume calculator does the same in a more abstract geometry form.