Well Volume Calculator — Water in a Well Casing
A water well is essentially a cylinder. Enter the inside diameter of the well casing and the depth of the water column to instantly find the stored water volume in US gallons, litres, cubic feet, and cubic metres.
Unit system
in
ft
Volume of standing water in the well casing
111 L
- 1
Radius (diameter ÷ 2)
6 in ÷ 2 = 3 in - 2
Column height in inches
20 ft × 12 = 240 in - 3
Volume (cylinder)
π × 3² × 240 = 6,786 in³V = π × r² × h — cylinder volume formula. - 4
Volume in litres
6,786 in³ × 0.004329 × 3.785 = 111.2
How does this calculator work?
A well's water volume follows the cylinder formula V = π × r² × h. For a 6-inch (0.152 m diameter) well with 20 ft (6.1 m) water column: r = 0.076 m, V = π × 0.076² × 6.1 ≈ 0.111 m³ = 111 L = 29 US gallons.
Formula
How this is calculated
A drilled well consists of a cylindrical casing (steel or PVC pipe) that extends from ground level down to and into the water-bearing aquifer. The water volume stored in the well depends only on the inside diameter of the casing and how deep the water column is — it has nothing to do with the pump or yield rate.
The formula is the standard cylinder volume: V = π r² h, where r is the inside radius and h is the height of the standing water column (not the total well depth). The inside diameter of residential wells in the US is most commonly 4–6 inches; agricultural and municipal wells can be 8–24 inches.
This stored volume (the 'well storage') is relevant for two practical purposes: (1) estimating how long a well can supply water during a pump failure before the casing runs dry; and (2) chlorination — when shock-chlorinating, you need to know the volume to dose correctly (typically 1 cup of bleach per 100 US gallons for routine disinfection). Well yield (gallons per minute from the aquifer) is a separate measurement that requires a pump test.
Frequently asked questions
Water column depth = total well depth − static water level (the depth at which water stands when the pump is off). For example: well drilled to 200 ft, static water level at 60 ft → water column = 140 ft. Your well driller's report should list both figures.
A 6-inch-diameter well with 100 feet of water column holds about 147 US gallons (555 L). A 4-inch well with the same water column holds only 65 gallons (247 L). Storage is less important when the aquifer recharge rate (yield) is high, but critical in low-yield wells.
The standard EPA recommendation for routine shock chlorination is approximately 1 cup (236 mL) of unscented household bleach (5.25–6% sodium hypochlorite) per 100 US gallons of well water. Use your calculated volume to determine the total bleach needed. For heavy contamination, increase the dose and consult a licensed well contractor.
Also known as
TG we-Calculate Editorial Team. (2026). Well Volume Calculator — Water in a Well Casing [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/well-volume-calculator
TG we-Calculate Editorial Team. "Well Volume Calculator — Water in a Well Casing." TG we-Calculate. 2026. https://we-calculate.com/calculator/well-volume-calculator.
TG we-Calculate Editorial Team, "Well Volume Calculator — Water in a Well Casing," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/well-volume-calculator
@misc{wecalculate_well_volume_calculator, title = {Well Volume Calculator — Water in a Well Casing}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/well-volume-calculator}}, year = {2026}, note = {TG we-Calculate} }
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