Aquifer Yield Calculator

Reviewed by the CalculatorHub team, edited by James Graham. Uses transmissivity-based well yield formula per USGS. Last verified 14 June 2026.

This calculator estimates well yield and aquifer transmissivity for a confined aquifer. It uses the simplified specific capacity to transmissivity relationship, and also computes transmissivity from hydraulic conductivity and aquifer thickness. For full Theis equation analysis using time-drawdown data from a pumping test, refer to USGS Groundwater Techniques publications. Enter aquifer properties to estimate sustainable yield and drawdown.

Hydraulic Conductivity K (m/day) Aquifer hydraulic conductivity (sand: 1-100 m/day, gravel: 100-1000 m/day)

Saturated Aquifer Thickness b (m) Thickness of the water-bearing zone (metres)

Well Radius r(w) (m) Drilled or effective well radius (typical: 0.10-0.30 m)

Allowable Drawdown s (m) Maximum acceptable water level decline (confined aquifer: up to 90% of head; unconfined: 50-75%)

Pumping Duration (days) Duration of continuous pumping for drawdown estimate

Storativity S (fraction) Confined aquifer: 0.0001-0.001; Unconfined (specific yield): 0.05-0.35

Transmissivity T (m2/day)

Estimated Yield (m3/day)

Estimated Yield (L/s)

Estimated Yield (US gpm)

Aquifer yield estimation formula

T = K x b Q = (4 x pi x T x s) / W(u) u = r(w)2 x S / (4 x T x t)

Where T = transmissivity (m2/day), K = hydraulic conductivity (m/day), b = aquifer thickness (m), Q = pumping rate (m3/day), s = drawdown (m), W(u) = Theis well function, r(w) = well radius (m), S = storativity, t = pumping time (days). W(u) is approximated here using the Cooper-Jacob approximation: W(u) = -0.5772 - ln(u), valid when u is less than 0.05. Source: USGS Techniques of Water-Resources Investigations, Book 3, Chapter B1 (Driscoll, 1986).

Aquifer yield calculator: frequently asked questions

What is aquifer yield?

Aquifer yield is the volumetric flow rate (Q) that a well can sustain from an aquifer without excessive drawdown. It is typically expressed in gallons per minute (gpm) or litres per second (L/s). Sustainable yield depends on aquifer transmissivity, storativity, well radius, and allowable drawdown.

What is transmissivity?

Transmissivity (T) is the rate at which groundwater moves horizontally through a unit width of the saturated aquifer under a unit hydraulic gradient. T = Hydraulic Conductivity (K) x Saturated Aquifer Thickness (b). Units are m2/day or gallons per day per foot. It is the primary aquifer parameter controlling well yield.

What is the Theis equation?

The Theis equation (1935) describes non-steady state groundwater flow to a well in a confined aquifer: s = (Q / (4 pi T)) x W(u), where s is drawdown (m), Q is pumping rate (m3/day), T is transmissivity (m2/day), and W(u) is the well function evaluated at u = r2S/(4Tt). It is the standard USGS method for aquifer test analysis.

What is storativity (storage coefficient)?

Storativity (S) is the volume of water released from or stored in aquifer storage per unit area per unit head change. For confined aquifers, S typically ranges from 0.0001 to 0.001. For unconfined (water table) aquifers, S equals specific yield, typically 0.05 to 0.35.

How is specific capacity different from aquifer yield?

Specific capacity (SC) is the pumping rate divided by drawdown: SC = Q / s. It is measured from a step-drawdown test and incorporates both aquifer properties and well efficiency. SC gives a practical measure of well performance but does not directly give the sustainable aquifer yield without additional analysis.

Official sources

USGS Techniques of Water-Resources Investigations: Basic Groundwater Hydrology (Heath, 1983, TWRI 3-B1).
USGS Office of Groundwater: USGS Groundwater Science.

Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.