Our own sizing calculator is one of the most useful first steps for a well system — but getting the tank size right isn't the same thing as getting the system right.
A correctly sized tank paired with the wrong settings elsewhere in the system can still short-cycle, run weak, or wear out a pump early. It isn't the finish line — it's one input among several.
Tank sizing answers one question: how much usable drawdown capacity do you need, given your pump's flow rate (GPM) and how many cycles per hour you want the pump to run at most. That's a real, important number — an undersized tank will always short-cycle a pump no matter what else is right. But it's one input among several, not the finish line.
Three other settings determine whether a correctly sized tank actually performs well:
A correctly sized tank that still performs badly: a homeowner buys the size our calculator recommends, installs it, and still gets short-cycling. The tank is fine — the precharge was set at the factory default instead of matched to the actual pressure switch settings, or it lost air over a couple of years and nobody rechecked it. The tank gets blamed and replaced with an even bigger one, which doesn't fix anything, because the tank was never the problem.
Before assuming you need a different tank size: check the precharge pressure with the system fully depressurized (cheapest possible fix, five minutes with a tire gauge), confirm the pressure switch cut-in/cut-out settings match what the tank is rated for, and confirm your pump's rated GPM against your well's actual yield. For most systems, one of those three turns out to be the actual issue, not the tank size.
Sizing the tank correctly is still the right place to start; it rules out the most common single cause of short-cycling. Just don't stop there, and don't let anyone (including us) tell you a bigger tank is the fix before those three other settings have been checked.
Check your precharge and pressure switch settings next — most "wrong tank size" problems turn out to be one of these two.
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