Well Pressure Tank Sizing Guide: What Size Do You Need?

Pressure Tank Basics

What Does a Pressure Tank Do?

• Stores pressurized water for immediate use
• Maintains consistent water pressure
• Reduces pump cycling (on/off cycles)
• Protects pump motor from overheating

How It Works

The tank contains a rubber bladder. Air above the bladder compresses as water fills the tank. When you use water, the compressed air pushes water out without the pump running—until pressure drops to the "cut-in" point and pump starts again.

Ideal Pump Cycle

• Pump runs 1-2 minutes per cycle
• Pump stays off 5+ minutes between cycles
• Maximum 6-8 cycles per hour

Understanding Drawdown

What Is Drawdown?

Drawdown is the usable water stored in the tank between pump cycles. It's NOT the total tank size—it's typically 25-35% of the tank's total capacity.

Drawdown vs Total Capacity

Note: Exact drawdown depends on pressure settings (30/50, 40/60, etc.) and tank brand.

How to Size Your Pressure Tank

The Simple Rule

Minimum drawdown (gallons) = Pump flow rate (GPM)

For a 10 GPM pump: Need at least 10 gallons drawdown = 32-44 gallon tank minimum

The Better Rule

For longer pump life and better performance, size up:

• Good: 1 gallon drawdown per GPM
• Better: 1.5 gallons drawdown per GPM
• Best: 2+ gallons drawdown per GPM

Step-by-Step Sizing

1. Determine your pump's GPM (check pump label or specs)
2. Multiply GPM × 1.5 for recommended drawdown
3. Select tank with that drawdown capacity or larger

Example Calculation

Pressure Tank Size Recommendation Chart

Problems with Undersized Tanks

Rapid Cycling (Short Cycling)

The pump turns on and off too frequently. Signs include:

• Clicking pressure switch every few seconds
• Pump running multiple times per minute
• Lights flickering when pump cycles

Pump Motor Damage

Frequent starting is hard on motors:

• Starting uses 5-7× running amps
• Motor never cools properly
• Bearings and windings wear faster
• Result: Pump life cut from 12-15 years to 3-5 years

Higher Energy Costs

Motor starting current spikes waste electricity. Short cycling can increase pump energy use by 20-40%.

Pressure Fluctuations

Small tanks can't maintain steady pressure during moderate use, causing:

• Shower temperature fluctuations
• Inconsistent flow to appliances

When to Upgrade Your Pressure Tank

Signs You Need a Bigger Tank

• Pump cycles more than 6-8 times per hour
• Pump runs for less than 1 minute per cycle
• Pump has failed prematurely
• Pressure fluctuates noticeably during use

Upgrade Costs

• 32-gallon tank: $250-$400
• 44-gallon tank: $350-$500
• 62-gallon tank: $450-$650
• 86-gallon tank: $550-$800
• Installation: $150-$400

Cost Justification

A $500 tank upgrade can save a $2,500 pump replacement. The larger tank pays for itself by extending pump life.

We install Well-X-Trol (Amtrol) and Flexcon pressure tanks — industry-leading bladder tanks that outlast standard diaphragm models. Proper sizing with a quality tank can double your pump's lifespan.

Frequently Asked Questions

What size pressure tank do I need for my well?

Minimum: 1 gallon drawdown per GPM of pump flow. For most 10 GPM residential pumps, a 44-gallon tank is good; 62-86 gallon is better.

What happens if pressure tank is too small?

Rapid pump cycling, which overheats and damages the motor. Pump life is drastically reduced—from 12-15 years to potentially 3-5 years.

Can a pressure tank be too big?

Not really. Bigger tanks are better—more drawdown, less cycling, longer pump life. The only limits are space and budget.

How do I know if my tank is sized correctly?

Monitor pump cycles. If pump runs 1-2 minutes and stays off 5+ minutes during normal use, sizing is adequate.

What pressure tank size for a 1 HP pump?

1 HP submersible pumps typically produce 10-15 GPM. A 44-62 gallon tank is recommended.