# Well Volume Calculator

URL: https://speedycalculator.com/calculators/everyday-life/well-volume/
Last updated: 2026-10-25

> The well volume calculator works out how much water a well holds from its diameter, total depth and static water level, and the purge volume – three well volumes – needed before sampling or disinfecting.

## Inputs

- Casing inside diameter (in, cm, mm)
- Total well depth (ft, m, in, cm, yd)
- Depth to static water (ft, m, in, cm, yd)

## Results

- Water column
- Well volume (water)
- Three well volumes (purge)
- Water per foot of casing
- Total casing volume

## Formula

```
Water column = total depth − depth to static water
Well volume = π ÷ 4 × diameter² × water column
Purge volume = 3 × well volume
```

## Explanation

Groundwater sampling protocols usually require purging three to five well volumes so that the sample represents fresh aquifer water, not stagnant water in the casing. Well volume also tells you how much chlorine is needed for shock chlorination and how much water storage the well provides.

### How to use the Well Volume Calculator

- **Casing inside diameter**
- **Total well depth**
- **Depth to static water**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the inside diameter of the casing, the total well depth and the depth from the top of the casing to the water.

### Tips

- Use the figures printed on your product or its manual when you have them.
- Round quantities up so you are never short.
- Measure twice before you buy anything cut to size.
- Everything runs in your browser – try different values to compare options.

### Common mistakes to avoid

- Mixing units (inches and centimetres, mAh and Ah).
- Ignoring efficiency losses and safety margins.
- Treating rules of thumb as exact.

### Inputs explained

FieldWhat to enterCasing inside diameterUnits: in, cm, mmTotal well depthUnits: ft, m, in, cm, ydDepth to static waterUnits: ft, m, in, cm, yd

### What each result means

- **Water column** = max([Total well depth] - [Depth to static water], 0)
- **Well volume (water)** = pi÷4×[Casing inside diameter]^2×[Water column]
- **Three well volumes (purge)** = 3×[Well volume (water)]
- **Water per foot of casing** = pi÷4×[Casing inside diameter]^2×0.3048
- **Total casing volume** = pi÷4×[Casing inside diameter]^2×[Total well depth]

### Example values

How the main result changes when **Casing inside diameter** changes and everything else stays at the example values above:

Casing inside diameter (in)Well volume (water) (US gal)355.14.5123.96220.37.5344.29495.712881.3

## Worked example

Inputs — Casing inside diameter: 6 in; Total well depth: 200 ft; Depth to static water: 50 ft.

Results — Water column = 150 ft; **Well volume (water) = 220.3 US gal**; Three well volumes (purge) = 661 US gal; Water per foot of casing = 1.469 US gal; Total casing volume = 294 US gal.

## FAQ

**How much water is in a 6-inch well per foot?**
About 1.47 gallons (5.6 L) per foot of water column.

**Why purge three well volumes?**
So the sample comes from fresh aquifer water rather than water that has stood in the casing.

**How do I measure the static water level?**
With an electric water-level meter or a weighted tape lowered until it touches water.

**What formula does the Well Volume Calculator use?**
Water column = total depth − depth to static water.


## Sources

- [U.S. EPA – Groundwater sampling guidelines](https://www.epa.gov/quality)