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.
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.
How long can I pump my well before it runs dry?
The time before a well runs dry depends on two factors: the standing volume of water and the well recovery rate (how fast water flows back into the well from the surrounding aquifer). If you only consider standing volume, a 220-gallon well pumped at 10 gallons per minute would empty in 22 minutes. However, the well simultaneously refills from the aquifer, so the actual pumping time is longer. The recovery rate (also called well yield) varies enormously from less than 1 gallon per minute in poor formations to over 50 GPM in productive aquifers. A well with 220 gallons of storage and a 5 GPM recovery rate being pumped at 10 GPM would run dry in about 44 minutes. To avoid running your well dry, the general guideline is to set your pump rate at or below the tested recovery rate. Running a well dry can damage the pump and potentially collapse the well bore in unconsolidated formations.
What is well yield and how is it different from well volume?
Well volume is the total amount of standing water in the well at a given moment (a static measurement), while well yield is the rate at which water flows into the well from the surrounding aquifer (a dynamic measurement in gallons per minute or per hour). A well can have a small standing volume but a high yield, meaning it refills quickly and can sustain continuous pumping. Conversely, a large-diameter deep well might have substantial standing volume but poor yield, meaning it takes hours to refill after being drawn down. Well yield is typically measured during a pump test, where the well is pumped at a known rate while monitoring the water level drawdown and recovery. The standard residential pump test lasts 4 to 24 hours. A minimum yield of 3 to 5 gallons per minute is generally considered adequate for most single-family households with typical domestic water usage patterns.