Well Yield & Flow-Rate Test Calculator
Measure a rough flow rate with a bucket and a stopwatch. Enter the gallons you collected and how many seconds it took — the calculator returns gallons per minute. A quick bucket test is a snapshot, not a sustained-yield test.
Calculator
Collecting 5.0 gallons in 30 seconds is about 10.0 gpm (gallons ÷ seconds × 60). A quick bucket test is a rough snapshot — a driller runs a longer draw-down test to find the well’s sustainable yield.
A bucket test is the fastest way to put a real number on how fast water flows from a tap, a hose bib, or a running pump. Catch a known volume, time it, and this calculator converts seconds into gallons per minute. It is a genuine reading of the flow at that moment — but, as the notes below explain, it is not the same as the well’s sustainable yield, which needs a longer draw-down test.
Formula
Flow rate in gallons per minute is the volume collected divided by the seconds it took, scaled to a full minute:
GPM = gallons ÷ fill seconds × 60
That is all a bucket test is: catch a known volume, time it, and convert seconds to minutes. It measures the flow at that moment from that outlet — useful for a tap, a hose bib or a quick check of what a pump is delivering.
Worked example
You catch 5 gallons in 30 seconds:
5 ÷ 30 × 60 = 10 GPM
The outlet is flowing at about 10 GPM right now. That is a genuine reading of the instantaneous flow, but it does not tell you the well’s sustainable yield — a well can deliver 10 GPM for a few minutes while the stored water in the casing is drawn down, then drop as it starts relying on the aquifer’s recovery.
Instantaneous flow vs. sustainable yield
There is an important difference between instantaneous flow and sustainable yield. A bucket test measures instantaneous flow: how fast water comes out at that instant. Sustainable yield is how many gallons per minute the well can keep producing for hours without the water level dropping to the pump. A well with a lot of water standing in a deep casing can flow strongly at first and then fall off as it depends on the aquifer refilling it.
To estimate sustainable yield properly, a driller runs a longer draw-down and recovery test: they pump the well at a steady rate, watch how far the water level falls and whether it stabilizes, then measure how quickly it recovers after the pump stops. That is the number that tells you whether the well can serve the household’s daily water use and support the peak demand you sized.
Still, the bucket test is worth doing. It confirms a pump is delivering roughly what it should, flags a clogged screen or a failing pump when the flow is far below normal, and gives you a real number to compare against your demand. For a fair reading, run the outlet wide open, let it stabilize for a few seconds before you start timing, and repeat the test a couple of times.
Frequently asked questions
How do I test my well's flow rate?
Run an outlet wide open into a container of known volume — a 5-gallon bucket works well — and time how long it takes to fill. Gallons divided by seconds, times 60, is the flow in GPM. Let the flow stabilize for a few seconds before timing and repeat once or twice.
Is a bucket test the same as a well yield test?
No. A bucket test measures the instantaneous flow at that moment. A true yield test pumps the well steadily for a longer period to see whether the water level holds and how fast it recovers. A well can flow strongly for a few minutes and then drop as it starts relying on the aquifer.
What is a good well flow rate?
Many homes are comfortable when the well sustainably yields 5 GPM or more, though lower yields work with storage. What matters is that the sustainable yield and daily recovery can cover your household’s daily use and peak demand. If it cannot, a storage or larger pressure tank bridges the gap.
Why time the fill in seconds?
Seconds give a more accurate reading for a fast flow than trying to time a full minute. The formula scales it back up: gallons ÷ seconds × 60. Timing a 5-gallon fill that takes 30 seconds is easier and more precise than eyeballing gallons-per-minute directly.