Well Volume Calculator
6" Well ≈ 1.469 Gallons per foot
Determine the exact storage capacity of your private well with our specialized Well Volume Calculator. Essential for homeowners and professional drillers alike, this tool provides instant estimates for shock chlorination, pump sizing, and drought planning.
Quick Estimate: A standard 6-inch well holds about 1.47 gallons per foot, while a 4-inch well holds 0.65 gallons per foot. Enter your specific measurements below for a precise calculation.
- Accurate for all standard casing sizes
- Converts to Gallons, Liters, or Cubic Feet
- 100% Free - No login required
Introduction to Well Volume
Well volume refers to the total amount of standing water stored within the cylindrical casing of a water well. Unlike a pool or a tank, the volume of a well is determined by the "water column"—the distance from the static water level down to the bottom of the well. For property owners relying on private water systems, understanding this volume is a critical component of responsible maintenance and emergency preparedness.
Whether you are preparing to "shock" your well with chlorine to remove bacteria or calculating if your storage is sufficient for peak summer demand, an accurate volume measurement is the starting point. Our calculator simplifies this process by applying hydraulic formulas to standard well dimensions, giving you professional-grade results in seconds.
How to Use the Well Volume Calculator
To get an accurate reading of your well's water storage, follow these simple steps:
- Select Well Diameter: Choose the inside diameter of your well casing from the dropdown menu. Most residential wells in North America are 4 or 6 inches.
- Enter Water Column Depth: This is the distance from the top of the water to the bottom of the well. Note: This is NOT the total depth of the well, but the depth of the water itself.
- Choose Output Unit: Select whether you want the result in Gallons (standard for chemical dosing), Liters, or Cubic Feet.
- View Results: The tool automatically updates as you change values, showing you the total volume and a handy reference for gallons per foot.
How the Calculation Works
The calculation uses the geometric formula for a cylinder to determine the space inside the casing. Because we are dealing with standard well units (inches for diameter and feet for depth), several conversion steps are performed behind the scenes.
The core formula is:
Volume = π × (Radius)² × Depth
To convert this to gallons:
1. Convert the diameter from inches to feet (Diameter / 12).
2. Find the radius in feet (Diameter in feet / 2).
3. Calculate volume in cubic feet: π × r² × depth.
4. Multiply cubic feet by 7.48 to get US Gallons.
Key Factors Affecting Well Volume
While the math is precise, the physical reality of your well can vary based on several environmental factors:
- Static Water Level: This level changes seasonally. In many regions, the water table drops in late summer, reducing your total stored volume.
- Well Recovery Rate: Your well's "volume" is just the storage. If you have a high recovery rate, the well refills as you pump, effectively giving you more water than just the static volume.
- Casing Integrity: Old steel casings can accumulate scale or sediment at the bottom, which may reduce the effective depth and volume over several decades.
Assumptions and Limitations
Our calculator provides a high-confidence estimate based on the following:
- Uniform Casing: We assume the well has a consistent diameter from top to bottom. Some very deep wells may change casing sizes halfway down.
- True Verticality: Calculations assume a perfectly vertical well. Significant deviation from vertical could lead to a slight overestimation of volume.
- Standard Gallons: All "Gallon" results are in US Liquid Gallons (1 US Gallon = 3.785 Liters).
3 Practical Well Volume Examples
1. Modern Residential Well
A standard 6-inch casing with 100 feet of standing water.
Volume: 146.9 Gallons
Calculated at ~1.47 gal/ft
2. Shallow Bored Well
An older 24-inch bored well with only 15 feet of water column.
Volume: 352.4 Gallons
Larger diameter = high storage
3. Deep Drilled (Narrow)
A 4-inch deep rock well with 250 feet of standing water.
Volume: 163.2 Gallons
Narrower casings hold less per foot
Quick Reference Table
Standard storage volumes for common well casing sizes per foot of water depth.
| Casing Diameter | Gallons per Foot | Liters per Foot | Cubic Feet per Foot |
|---|---|---|---|
| 4 inches | 0.653 gal | 2.47 L | 0.087 ft³ |
| 6 inches | 1.469 gal | 5.56 L | 0.196 ft³ |
| 8 inches | 2.611 gal | 9.88 L | 0.349 ft³ |
| 24 inches | 23.49 gal | 88.94 L | 3.141 ft³ |
| 36 inches | 52.87 gal | 200.1 L | 7.069 ft³ |
Frequently Asked Questions
How do I find my well diameter?
The easiest way is to look at your well cap. Most modern caps have the diameter stamped on them. If not, measure the distance across the outside of the casing—standard diameters are 4, 5, or 6 inches.
What is the "Water Column"?
This is the vertical distance between the static water level (the surface of the water) and the bottom of the well. It is the actual "tube" of water stored in the well.
How much chlorine do I need to shock a 6-inch well?
Most health departments recommend approximately 3 pints of 5.25% bleach for every 100 gallons of water. Use this calculator to find your total gallons first!
Why does my well volume matter for my pump?
The stored volume acts as a buffer. If your pump's flow rate (GPM) is higher than the well's recovery rate, the pump relies on this stored volume to prevent running dry.
Conclusion
Knowing your well volume is more than just a math exercise—it's a fundamental part of maintaining a healthy and reliable home water supply. By using our Well Volume Calculator, you can confidently plan for maintenance, shock treatments, or high-usage periods. Bookmark this page to keep this essential tool ready for your next annual well inspection or water system upgrade.