Well Volume Calculator
How much water is standing in a drilled well, from the casing’s inside diameter, the well depth and the depth to the water.
Result
Buy 220.3 gal
Counts the standing water in the casing only, not the pipe or pressure tank.
- Height of the water column
- 150 ft (1,800 in, 45.72 m)
- Weight of that water
- 1,839 lb (834 kg)Estimate
https://calcgallery.com/home-systems/well-volume-calculator/
Results are estimates for planning only. Actual needs vary with site conditions, products and workmanship. Always confirm quantities with your supplier and follow local building codes and manufacturer instructions. Read the full disclaimer
How to use the Well Volume Calculator
- Enter the casing's inside diameter, from the well record or by measuring inside the casing.
- Enter the well's total depth and the depth down to the water, both measured from the top of the casing.
- Read the gallons or litres standing in the well and the height of the water column.
The water column
water column = well depth − depth to watervolume = π × (casing inside diameter ÷ 2)² × water columnThe water in a drilled well stands as a cylinder inside the casing, from the static water level to the bottom. A well can be hundreds of feet deep and still hold only a few hundred gallons, because the casing is narrow: a 6-inch casing holds about 1.47 gallons a foot, a 4-inch one about 0.65.
Measuring from one point
Both depths must be measured from the same reference, normally the top of the casing. If the well record gives depths from the ground and the casing stands a foot above it, add that foot to both or to neither. The answer depends only on the difference between them.
With your numbers
- Volume = π × (casing diameter ÷ 2)² × (well depth − depth to water)
Quick reference
Counts the standing water in the casing only, not the pipe or pressure tank.
| Job | Water in the well |
|---|---|
| 6 in well, 200 ft, water at 50 ft | 220.3 gal |
| 4 in well, 150 ft, water at 30 ft | 78.3 gal |
| 6 in well, 400 ft, water at 100 ft | 440.6 gal |
| 8 in well, 120 ft, water at 20 ft | 261.1 gal |
| 36 in dug well, 30 ft, water at 10 ft | 1,057.5 gal |
| 15 cm well, 60 m, water at 12 m | 848.2 L |
Where the numbers come from
The fixed figures this calculator relies on, and the published source each one was checked against. How the calculators are built and checked
1 source
NIST Chemistry WebBook, water at 4 °C and 0.101325 MPa: 999.9749 kg/m³ (IAPWS-95), https://webbook.nist.gov/cgi/fluid.cgi?ID=C7732185, rounded to the conventional 1000 kg/m³ of NIST SP 811 (2008) Appendix B, centimeter of water, conventional = 98.0665 Pa.
Used for
- The conventional density of water, 1000 kg/m³. Pure water at 4 °C, its densest, is 999.97 kg/m³.
Common questions about the Well Volume Calculator
- How many gallons are in my well?
- Multiply the casing’s cross-section by the height of the water in it. A 6-inch well 200 feet deep with water at 50 feet has 150 feet of water, and each foot of 6-inch casing holds about 1.47 gallons, so about 220 gallons are standing in it.
- How do I find the depth to water?
- It is on many well records as the static water level. To measure it, turn the pump off long enough for the level to recover, then lower a weighted tape or a water level meter until it touches the water, reading from the top of the casing.
- Why would I need the volume of water in my well?
- Shock chlorination and purging procedures are written around it: how much disinfectant to add, or how many well volumes to pump out before sampling. Take the procedure itself, and any dose, from your local or state health department, since they differ; this page gives only the volume.
- Does this include the water in the pipes and pressure tank?
- No, only the water standing in the casing. The pipe volume and tank volume pages give those if a procedure calls for the whole system.