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Well Yield Calculator

Work out well yield instantly with clear inputs, formula shown and shareable results.

About Well Yield Calculator

Specific capacity, the pumping rate divided by the drawdown it causes, is the single most useful number from a well test because it predicts how the well will behave at other rates. Sustained abstraction is normally set at about 70 percent of the tested rate so the aquifer is not drawn down to the pump intake in dry seasons.

Formulas

Specific capacity

Sc = test flow GPM / drawdown ft

Sustainable rate

Recommended GPM = 0.7 x tested rate

Worked example

With the default values below, Well Yield Calculator returns Specific capacity of 0.343. Change any input above and every figure here is recalculated in your browser.

Inputs used

Static water levelminimum 0 ft
40 ft
Level while pumpingminimum 0 ft
75 ft
Test pumping rateminimum 0.1 GPM
12 GPM
Test durationminimum 1 min
60 min

Results

Specific capacity
0.343 GPM per ft
Drawdown
35.0 ft
Recommended continuous rate
8.40 GPM
Volume pumped in test
720 gal

Step by step

  1. 1Values used
  2. 2Specific capacity
  3. 3Sustainable rate
  4. 4Specific capacity= 0.343 GPM per ft
  5. 5Drawdown= 35.0 ft
  6. 6Recommended continuous rate= 8.40 GPM
  7. 7Volume pumped in test= 720 gal

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Well Yield figure worked out?

Sc = test flow GPM / drawdown ft. Specific capacity, the pumping rate divided by the drawdown it causes, is the single most useful number from a well test because it predicts how the well will behave at other rates.

Why not pump at the full tested rate?

A short test does not reveal seasonal decline or interference from nearby wells. The margin protects the pump from breaking suction when water levels fall.

What values do I need to enter?

This calculator takes 4 inputs: Static water level, Level while pumping, Test pumping rate, Test duration. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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