Well Volume Calculator
Calculate well volume easily with our free tool. Get practical results, tips, and comparisons for everyday decisions. Free to use with no signup required.
Reviewed by Daniel Agrici, Founder & Lead Developer
Formula
Volume = Pi x (Diameter / 2)^2 x (Total Depth - Static Water Level) x 7.48
Where Diameter is the well casing diameter in inches (converted to feet), Total Depth is the well depth in feet, Static Water Level is the depth to the water surface in feet, and 7.48 converts cubic feet to gallons. The water column height equals Total Depth minus Static Water Level.
Worked Examples
Example 1: Standard Residential Well Volume
Problem:A 6-inch diameter well is 200 feet deep with a static water level at 50 feet. Calculate the water volume.
Solution:Radius = 6 / 2 = 3 inches = 0.25 feet\nWater column = 200 - 50 = 150 feet\nVolume = Pi x 0.25^2 x 150 = 29.45 cu ft\nGallons = 29.45 x 7.48 = 220.32 gallons\nLiters = 220.32 x 3.785 = 833.9 liters\nBleach for chlorination = 220/100 = 2.2 pints
Result:Volume: 220.3 gallons (833.9 L) | Water column: 150 ft | Bleach: 2.2 pints
Example 2: Deep Well Pump Time Calculation
Problem:An 8-inch well is 400 feet deep with 80-foot static water level. Pump rate is 15 GPM. How long to pump out?
Solution:Radius = 8 / 2 = 4 inches = 0.333 feet\nWater column = 400 - 80 = 320 feet\nVolume = Pi x 0.333^2 x 320 = 111.5 cu ft\nGallons = 111.5 x 7.48 = 834.1 gallons\nPump time = 834.1 / 15 = 55.6 minutes = 0.93 hours\nNote: actual time is longer due to aquifer recharge
Result:Volume: 834.1 gallons | Pump-out time: 55.6 min (without recharge) | 2.8 days household storage
Frequently Asked Questions
How do I calculate the volume of water in my well?
Well volume is calculated using the cylinder volume formula: Volume = Pi times radius squared times height, where the radius is half the well casing diameter and the height is the water column (total well depth minus the static water level). The static water level is the depth from the ground surface to where water naturally sits in the well without pumping. For a 6-inch diameter well that is 200 feet deep with a static water level at 50 feet, the water column is 150 feet. The radius is 3 inches (0.25 feet), giving a volume of Pi times 0.25 squared times 150 equals 29.45 cubic feet, which converts to approximately 220 gallons. This represents the standing water volume available in the well at any given time.
How many gallons per foot of water are in my well?
Gallons per foot depends entirely on the well casing diameter. Common values are 2-inch well yields 0.163 gallons per foot, 4-inch well yields 0.653 gallons per foot, 6-inch well yields 1.469 gallons per foot, 8-inch well yields 2.611 gallons per foot, 10-inch well yields 4.08 gallons per foot, and 12-inch well yields 5.875 gallons per foot. These values are calculated using the formula Pi times (radius in feet) squared times 7.48052 gallons per cubic foot. For example, a 6-inch well has a radius of 0.25 feet, so Pi times 0.0625 times 7.48052 equals 1.469 gallons per foot. Multiply the gallons-per-foot value by your water column height (total depth minus static water level) to get total well volume. This calculation assumes the well bore is the same diameter as the casing throughout its depth.
How much bleach do I need to shock chlorinate my well?
The standard recommendation for well shock chlorination is 1 pint (16 fluid ounces) of unscented household bleach (5.25 to 8.25 percent sodium hypochlorite) per 100 gallons of well water volume. For a well containing 200 gallons, you would need 2 pints (1 quart) of bleach. Some state health departments recommend a stronger solution of 3 pints per 100 gallons for heavily contaminated wells. After adding bleach, run water from each faucet until you smell chlorine, then let the solution sit for 12 to 24 hours without using any water. After the contact period, flush the system by running water through an outdoor hose to a safe discharge area until the chlorine smell dissipates completely. Never discharge chlorinated water into septic systems, streams, or ponds. Retest the water 7 to 10 days after chlorination to confirm bacteria levels are safe.
What well diameter is standard for residential water wells?
Residential water wells in the United States most commonly use 6-inch diameter casing, which provides a good balance between cost, pump sizing, and water capacity. A 6-inch well accommodates 4-inch submersible pumps (the most common residential pump size) with adequate clearance for installation and maintenance. Smaller 4-inch wells are used in some regions and work with 3-inch pumps but provide less water storage per foot of depth. Larger 8-inch casing is sometimes specified for high-demand households, agricultural wells, or areas with low-yield formations where more storage is beneficial. In commercial and municipal applications, well casings can range from 10 to 24 inches or larger. The casing material is typically PVC in shallow wells (under 200 feet) and steel in deeper wells. State and local regulations often specify minimum casing diameter and material requirements.
References
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy