Well Yield Calculator

Enter your pumping test volume, duration, drawdown, and well dimensions to calculate yield, specific capacity, and daily water supply potential.

Created by Luis GonzalezLast updated: May 9, 2026

How to Use This Calculator

1
Input Pumped Test Volume
Enter the total volume of water, in gallons, pumped during your well drawdown test.
2
Specify Pumping Time
Provide the duration, in minutes, that the well was actively pumped during the test.
3
Enter Drawdown
Input the drop in water level, in feet, from the static level that occurred during the pumping test.
4
Record Static Water Level
Provide the depth to the water surface, in feet from the ground, before any pumping began.
5
Input Total Well Depth
Enter the total drilled depth of the well from the ground surface in feet.
6
Review Well Performance
Instantly see the well's yield in gallons per minute, hour, and day, along with specific capacity and pumping water level.

Example Calculation

A prospective buyer is evaluating the water supply for a rural property with a recently tested well.

Pumped Test Volume (gal)

5,000

Pumping Time (min)

Drawdown (ft)

Static Water Level (ft)

Well Depth (ft)

200

Results

166.7 gpm

Tips

Conduct a Proper Drawdown Test

For accurate results, ensure your drawdown test is conducted over a sufficient duration (e.g., 4-24 hours) and that the pumping rate is stable, allowing for the water level to stabilize.

Monitor Drawdown Carefully

Measure the drawdown accurately using a static water level meter. Small errors in this measurement can significantly affect the calculated specific capacity and overall yield assessment.

Consider Seasonal Variations

Well yield can fluctuate with seasons and local rainfall. Conduct tests during dry periods (e.g., late summer) to get a conservative estimate of the well's minimum sustainable yield.

Calculating Well Yield for Sustainable Water Resource Management

Accurately calculating well yield is a critical step for assessing the long-term viability of a water source, whether for residential, agricultural, or commercial use. This Well Yield Calculator helps you determine the sustainable pumping rate from a drawdown test, providing essential metrics like gallons per minute, specific capacity, and pumping water level. For any property owner, understanding a well's capacity, which can range from 5 GPM for residential use to hundreds for agriculture, is a key investment decision in 2025.

Why Well Yield is a Key Investment Factor

For investments in rural real estate, agriculture, or any venture reliant on groundwater, well yield is a paramount factor. It directly quantifies the sustainability and reliability of the water supply, influencing everything from crop irrigation capacity to the comfort of a household. A well with a robust and consistent yield enhances property value and reduces operational risks, whereas an insufficient or unstable yield can lead to significant additional costs for water hauling, new well drilling, or water treatment, thereby diminishing the investment's attractiveness and long-term viability.

The Hydrology Behind Well Yield Calculation

This calculator determines well yield by analyzing data from a controlled drawdown test, focusing on the volume of water pumped and the time taken.

Calculate Well Yield (GPM): This is the primary measure, representing the gallons pumped per minute.
```
Well Yield (GPM) = Pumped Test Volume (gal) / Pumping Time (min)
```
Calculate Hourly Yield (GPH): Converts GPM to an hourly rate.
```
Hourly Yield (GPH) = Well Yield (GPM) × 60
```
Calculate Daily Yield (GPD): Converts GPM to a daily rate.
```
Daily Yield (GPD) = Well Yield (GPM) × 1440
```
Calculate Pumping Water Level (ft): The depth of the water during the pumping test.
```
Pumping Water Level (ft) = Static Water Level (ft) + Drawdown (ft)
```
Calculate Specific Capacity (GPM/ft): Measures the well's efficiency.
```
Specific Capacity (GPM/ft) = Well Yield (GPM) / Drawdown (ft)
```
Calculate Usable Casing Storage (gal): Estimates the water stored in the well casing above the pump intake.
```
Usable Casing Storage (gal) = (Well Depth (ft) - Pumping Water Level (ft)) × (π × (Casing Radius (inches) / 12)² × 7.48)
```
(Note: Casing radius not an input, assuming a standard diameter or for illustrative purposes the formula is simplified by the calculator)

Here, Pumped Test Volume is the total water extracted, Pumping Time is the duration of the test, Drawdown is the drop in water level, Static Water Level is the initial water depth, and Well Depth is the total depth of the borehole.

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Worked Example: Evaluating a Farm's Water Source

A farmer is assessing a new well for irrigation. During a 30-minute pumping test, 5,000 gallons were extracted. The drawdown was 10 feet from a static water level of 50 feet in a 200-foot deep well.

Calculate Well Yield (GPM): Well Yield (GPM) = 5,000 gal / 30 min = 166.67 GPM
Calculate Hourly Yield (GPH): Hourly Yield (GPH) = 166.67 GPM × 60 = 10,000.2 GPH
Calculate Daily Yield (GPD): Daily Yield (GPD) = 166.67 GPM × 1440 = 240,004.8 GPD
Calculate Pumping Water Level: Pumping Water Level = 50 ft (Static) + 10 ft (Drawdown) = 60 ft
Calculate Specific Capacity: Specific Capacity = 166.67 GPM / 10 ft = 16.67 GPM/ft

The well yield is 166.7 gpm. This indicates a robust water supply capable of supporting significant irrigation needs.

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Assessing Water Resource Value for Agricultural & Real Estate Investments

Well yield is a critical factor for investments in agriculture and rural real estate, directly impacting property valuation and operational costs. For agricultural operations, a sustainable yield dictates irrigation capacity, with large farms often requiring 50-500 GPM to support extensive crop production. For rural homes, typical residential well yields of 5-15 GPM are needed for potable water supply, ensuring consistent access for daily needs. A reliable, high-yield well can significantly enhance a property's market value and reduce long-term operating expenses, while an insufficient yield can lead to costly water hauling or the need for new, expensive drilling projects.

Regulatory Standards for Well Yield and Water Rights

Well yield and specific capacity are often subject to a complex web of local, state, and national regulations, particularly in regions where water resources are scarce. These regulations typically govern well drilling permits, minimum yield requirements for different uses (e.g., residential vs. commercial), and the allocation of water rights. For instance, in many Western U.S. states, the "prior appropriation" doctrine dictates that water rights are granted to those who first put the water to beneficial use, irrespective of land ownership. Conversely, "riparian rights" in Eastern states often link water use to adjacent land ownership. Minimum residential well yields, such as 3-5 GPM, are frequently mandated by county health departments to ensure adequate potable water supply for new constructions, while agricultural pumping may face volumetric restrictions to protect groundwater tables.

Frequently Asked Questions

What is well yield and why is it important for property owners?

Well yield is the rate at which a well can continuously supply water, typically measured in gallons per minute (GPM). It's crucial for property owners because it determines if a well can meet household, irrigation, or livestock water demands. An insufficient yield can limit property use, impact value, and necessitate costly upgrades.

How does specific capacity relate to well yield?

Specific capacity is a measure of a well's efficiency, calculated by dividing the well yield (GPM) by the drawdown (feet). It indicates how much water the well produces per foot of water level drop. A higher specific capacity suggests a more efficient well, while a low value might indicate issues like clogged screens or poor aquifer connection.

What is a good well yield for a residential property?

For most residential properties, a well yield of 5-10 GPM is generally considered adequate for typical household needs, including multiple fixtures and appliances. However, properties with extensive irrigation or multiple occupants may require higher yields, sometimes up to 15-20 GPM, for comfortable and sustainable water use.

Can a well's yield change over time?

Yes, a well's yield can change due to various factors including seasonal water table fluctuations, prolonged drought, changes in nearby pumping, or well degradation (e.g., screen clogging, mineral buildup). Regular monitoring and occasional re-testing are recommended to ensure the well continues to meet water demands.