How do I know if my pressure tank is the right size?

A tank is the right size when the pump cycles on and off at a reasonable pace rather than rapidly. If the pump kicks on with small water use, the tank may be too small, waterlogged, or wrongly pre-charged.

How often should I check pre-charge?

Checking pre-charge once a year is reasonable, and any time you notice pressure problems or rapid cycling. The tank must be drained of water to read it accurately.

Well Pumps

Well Pressure Tank Basics: What It Does and Why It Matters

The pressure tank stores water under pressure so the pump does not run every time you open a tap. Here is how it works and why pre-charge matters.

By Know Your Well Water Editorial TeamReviewed October 29, 20262 min read

Quick Answer

A well pressure tank stores water under pressure so your pump does not start every time you open a faucet. Most modern tanks use an air bladder or diaphragm; the air pre-charge is typically set about 2 psi below the pump’s cut-in pressure. A correctly charged tank delivers steady pressure and protects the pump by reducing how often it cycles.

What the tank does

When the pump runs, it fills the tank and compresses the air inside. When you use water, that compressed air pushes water out to your fixtures without the pump running. Only when pressure drops to the cut-in setting does the pump turn back on. This buffer is what keeps the pump from short cycling and gives you smooth household pressure.

Pre-charge: the number that matters

Pre-charge is the air pressure in the empty tank, checked with the water drained.
It is typically set about 2 psi below the pump’s cut-in pressure.
For a 30/50 switch, that is around 28 psi; for 40/60, around 38 psi.
Too low or too high a pre-charge causes poor pressure or short cycling.

Why 2 psi below cut-in

Setting pre-charge just below cut-in ensures the tank still has a cushion of air to push out usable water before the pump restarts. Match pre-charge whenever the pressure-switch setting changes.

Sizing the tank

A larger drawdown (usable water between cut-in and cut-out) means fewer pump starts, which is gentler on the motor. Tank size is matched to the pump’s flow and the pressure settings. Our pressure-tank size calculator helps you understand the relationship between tank size, pressure settings, and cycling.

A failing tank shows up as cycling

If the tank loses its air charge or the bladder fails, the pump starts rapidly (short cycling). That is the most common sign a tank needs attention.

Frequently asked questions

How do I know if my pressure tank is the right size?: A tank is the right size when the pump cycles on and off at a reasonable pace rather than rapidly. If the pump kicks on with small water use, the tank may be too small, waterlogged, or wrongly pre-charged.
How often should I check pre-charge?: Checking pre-charge once a year is reasonable, and any time you notice pressure problems or rapid cycling. The tank must be drained of water to read it accurately.

Sources & references

Protect Your Home’s Water: Private Wells — US EPA, accessed October 29, 2026

This guide is documentary research and general information, not a laboratory analysis or professional assessment of your specific well. See our disclaimer.