How to Size a Well Pressure Tank

A properly-sized pressure tank is an integral part of maintaining your well. Well pressure tanks extend the lifespan of your well pump by preventing rapid on/off cycling of the pump and maintaining water pressure throughout your home. A properly sized pressure tank ensures your household water needs are met and protects your pump from short cycling.

What is a well pressure tank? How does a well pressure tank work? How to size your well pressure tank Well pressure tank size chart Recommended well pressure tanks Factors that affect the size of your well pressure tank Why proper tank sizing matters Frequently asked questions about well pressure tanks Guarantee long-term efficiency with the right well pressure tank

Whether you're installing a new system or replacing an old tank, understanding how to choose the right size based on your well's output is key. In this guide, we’ll walk you through the steps to properly size a well pressure tank for your home.

What is a well pressure tank?

A well pressure tank is a specialized storage tank used in private well systems to regulate water pressure and prevent damage to the well pump. It consists of several key components that work together to maintain steady water pressure throughout your home:

Tank: The tank holds both water and air, typically in separate chambers or sections.
Bladder or diaphragm: Many tanks have a flexible rubber bladder or diaphragm that separates the air from the water to prevent them from mixing.
Air chamber: When water fills the tank, the air chamber compresses, creating the pressure needed to push water through your plumbing system.
Pressure switch: The pressure switch monitors the tank's pressure and signals the well pump to turn on or off as needed.

The pressure tank reduces how often the well pump cycles on and off by holding a reserve of pressurized water to help prevent premature wear on the pump. Every time you turn on a faucet, flush a toilet, or run a bath, the pressure tank supplies water from its reserve, and the internal air bladder compresses to push water through the system. Once the water level in the tank drops below a certain point, the pressure switch triggers the well pump to replenish the tank.

How does a well pressure tank work?

A well pressure tank uses compressed air to regulate water pressure and maintain steady water flow throughout your home, ensuring a consistent flow rate from faucets and fixtures—even when multiple taps are running at once.

Here’s a step-by-step breakdown of how a well pressure tank works:

1. Water enters the tank

The pump draws water from the well into the tank. As water enters the tank, the pump compresses the air in the air chamber or bladder, creating pressure.

2. Pressure builds up

As more water enters, the air pressure inside the tank increases. The pressure switch is programmed to manage this process. In many household systems, the switch activates at a lower pressure of 30 psi and turns off the pump when the pressure reaches an upper limit, typically 50 or 60 psi. A gauge in front of the tank displays the current pressure, providing a visual indicator for system performance.

3. Water is supplied to the home

When you turn a faucet or appliance on, the compressed air in the tank pushes water out through the plumbing system. This allows water to flow without needing to turn the pump on immediately.

4. Pressure drops & the pump reactivates

As the stored water is used, pressure inside the tank decreases. Once the pressure reaches the lower limit (e.g., 30 psi), the pressure switch signals the pump to turn back on. The cycle repeats, maintaining a steady water supply.

How to size your well pressure tank

Properly sizing your well pressure tank is crucial for maintaining stable water pressure, reducing pump wear, and preventing short cycling. Here's how to size a pressure tank.

1. Find your pump’s flow rate (GPM)

The pump flow rate, measured in gallons per minute (GPM), indicates how much water your well pump can deliver. This is critical for determining the tank size, as a tank that's too small for your pump will cause frequent cycling, leading to premature pump failure. Conversely, a tank that’s too large can lead to inefficient operation.

How to measure your pump's flow rate:

Fill a 1-gallon container with water from your system.
Time how long it takes to fill the container (e.g., 10 seconds).
Use the formula: Flow rate (GPM) = 60 seconds ÷ fill time
Example: If it takes 10 seconds, your flow rate is 6 GPM (60 ÷ 10 = 6).

2. Calculate minimum runtime and drawdown capacity

Your pump needs a minimum runtime to prevent short cycling, which can damage the pump. The drawdown capacity is the amount of usable water stored in the tank between pump cycles. Use the formula:

Tank size (gallons) = Pump flow rate (GPM) × Minimum runtime (minutes) × Multiplier

Pumps with a flow rate of 10 GPM or less should run for at least 1 minute, meaning 10 gallons of drawdown capacity is needed.
Example: 10 GPM × 1 minute = 10 gallons
Pumps with a flow rate over 10 GPM require a multiplier of 1.5 minutes for runtime.
Example: 16 GPM × 1.5 minutes = 24 gallons
Pumps with a flow rate over 20 GPM may require multiple tanks for optimal performance.

3. Determine your pressure switch setting

The pressure switch controls when the pump turns on and off. Common pressure switch settings include 30/50 psi and 40/60 psi:

Cut-on pressure: The pressure at which the pump starts (e.g., 30 or 40 psi).
Cut-off pressure: The pressure at which the pump stops (e.g., 50 or 60 psi).

A system with a 30/50 switch will have more drawdown capacity than one with a 40/60 switch. Most manufacturers provide charts to help match your tank’s drawdown capacity with the appropriate pressure switch setting.

Well pressure tank size chart

Pump Output Flow Rate (GPM)	Pump Minimum Run Time (Minutes)	Pressure Switch (psi)	Drawdown Needed (Gallons)	Minimum Tank Size (Gallons)
5	1	30/50	5	16.6
5	1	40/60	5	19.2
10	1	30/50	10	33.4
10	1	40/60	10	38.5
15	1.5	30/50	22.5	75
15	1.5	40/60	22.5	86.5
20	1.75	30/50	35	116.6
20	1.75	40/60	35	134.6

Recommended well pressure tanks

Pressure tank for 7-9 GPM

Pressure tank for 10-14 RPM pumps

WellMate WM-14WB Quick-Connect System Well Pressure Tank 47 gal

$987.66

in stock

Factors that affect the size of your well pressure tank

In addition to the pump's flow rate and pressure settings, consider these factors when choosing a tank size:

Household water demand

Your tank should be large enough to meet your household’s water needs without causing frequent pump cycles. Factors that influence water demand include:

Household size: More people mean more water use for showers, laundry, and dishwashing.
Number of fixtures and appliances: Consider sinks, toilets, washing machines, dishwashers, and irrigation systems.
Simultaneous usage: If multiple taps or appliances run at once, you’ll need a larger tank to avoid immediate pump activation.

Water yield and recovery rate

The well yield is the amount of water your well can produce per minute, while the recovery rate is how quickly the well refills.

High-yield wells (10+ GPM) can support continuous use.
Low-yield wells (under 5 GPM) may struggle to meet demand and could cause pump damage if the well runs dry.

If your well has a low yield, you may need a larger tank to compensate and prevent water shortages.

Desired pressure range

Most residential well pressure tanks operate within one of the following pressure ranges:

30–50 psi: Standard for most homes with moderate water demand.
40–60 psi: Provides higher pressure for large homes, multi-story houses, or homes with high water demand.

A higher pressure range offers stronger flow but reduces drawdown capacity, which may require a larger tank to minimize pump cycles.

Why proper tank sizing matters

A well-sized pressure tank helps:

Prevent short cycling: Reduces wear and tear on the pump by minimizing on/off cycles.
Maintain system pressure: Keeps water pressure stable, minimizing interruptions or delays while the pump cycles on to refill the tank.
Increase system efficiency: Protects the pump and plumbing from damage, extending their lifespan.

Frequently asked questions about well pressure tanks

What is drawdown?

Drawdown is the volume of usable water stored in the pressure tank, measured by the amount drawn between the pump's cut-off and cut-on pressures. This volume ensures the pump runs long enough to meet its minimum runtime, reducing wear from frequent cycling. It should not be confused with the total tank volume, which is the tank’s overall storage capacity. Drawdown ensures the pump does not turn on and off too frequently, protecting it from damage.

Is it okay to oversize a well pressure tank?

Yes–it’s virtually impossible for there to be a pressure tank that’s too large. The bigger the well pressure tank, the fewer pump cycles are required to fill the tank, therefore extending the life of the entire system. The only drawback of an oversized tank is the increased cost and size of the tank itself.

What is a tank package?

When purchasing a new pressure tank, it is important to also purchase a corresponding tank package, also called a t-pack. The t-pack attaches to the outlet of the well tank and hooks up to your inlet line from the well. These come with many of the necessary parts to operate and monitor your well pressure tank, including the pressure switch, pressure gauge, relief valve, tank cross, and ball valve.

Does a bigger well pressure tank increase water pressure?

No, a bigger well pressure tank does not increase water pressure. Water pressure is controlled by the pressure switch settings, not the tank size.

However, a larger tank helps maintain stable pressure by reducing pump cycling, which prevents sudden pressure drops during use. If you want higher water pressure, you need to adjust the pressure switch settings (if your pump and/or plumbing system can handle it) or install a booster pump.

How do I maintain my well pressure tank?

You should check the air pressure in the tank annually to make sure it’s at the proper level. The air pressure should be 2 psi below the pump’s cut-in pressure. For example, if your pump turns on at 40 psi, the empty tank pressure should be 38 psi.

You should also inspect the tank for signs of leaks or rust and monitor the pump cycling frequently to make sure the tank is the right size. You may also want to flush sediment from the system periodically to avoid clogging.

What is the lifespan of a well pressure tank?

A well pressure tank typically lasts 5-15 years, depending on the quality of the tank, the water quality, and how often the pump cycles. Properly sized well pressure tanks that are well-maintained tend to last longer.

Guarantee long-term efficiency with the right well pressure tank

Choosing the right size well pressure tank helps extend the lifespan of your well pump, ensures that your system operates smoothly, and saves on energy costs. By calculating pump flow rate, and pressure settings, you can select the ideal tank to meet your needs. With the right pressure tank in place, you can enjoy reliable water pressure and a more efficient well system for years to come.

The experts at Fresh Water Systems know a thing or two about well pressure tanks. For any project big or small, give us a call–we’re always happy to lend a hand.

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