# What Size Pressure Tank Do I Need for My Well?

> What size pressure tank you need for your well pump: a sizing chart by gallons per minute, the one-minute run rule, drawdown explained and common mistakes.

URL: https://waterwelldrillingweatherford.com/learn/what-size-pressure-tank-do-i-need/

Learn

Size the tank to the pump's output, not the house's square footage. A chart by gallons per minute, and why the one-minute rule matters.

Size the pressure tank so your pump runs **at least one minute per start**. That takes about **one gallon of drawdown per gallon per minute** of pump output. Tanks deliver roughly 30% of their nominal size as drawdown, so a **10 gpm pump needs about a 30–40 gallon tank**, and a 15 gpm pump needs about 50–60 gallons or more.

[Water Well Drilling Weatherford](https://waterwelldrillingweatherford.com/) resizes a lot of pressure tanks that were bought to match the old one rather than the pump. *What size pressure tank do I need?* has a simple answer once you know your pump’s flow rate.

## The one-minute rule

Submersible motor makers call for the motor to run **at least one minute** every time it starts, so it can shed the heat of the starting current. The pressure tank is what makes that possible. It stores enough water that the pump can run a full minute before the house pulls the pressure down again. Tanks that are too small cause short cycling. Short cycling burns out switches and motors.

## Sizing chart

About one gallon of drawdown per gpm gives a one-minute run. Tanks deliver roughly 30% of their nominal size as drawdown:

| Pump output | Drawdown needed | Minimum tank (nominal) | Common tank size |
| --- | --- | --- | --- |
| 5 gpm | ~5 gal | ~17 gal | 20 gal |
| 7 gpm | ~7 gal | ~23 gal | 32 gal |
| 10 gpm | ~10 gal | ~33 gal | 32–44 gal |
| 12 gpm | ~12 gal | ~40 gal | 44 gal |
| 15 gpm | ~15 gal | ~50 gal | 62 gal |
| 20 gpm | ~20 gal | ~67 gal | 86 gal |

Two smaller tanks piped together add up the same way as one large tank.

## Finding your pump’s flow

Check the pump’s model on your State Well Report or the service record. A tech can also time how long the pump takes to raise the tank from cut-in to cut-out while no water is being used, which gives the delivered gallons per minute. Parker County wells vary. A shallow Peaster well and a deep Aledo well with the same horsepower pump can deliver very different flows.

## Setting it up right

- **Pre-charge 2 psi below cut-in** with the system drained: 28 psi on a 30/50 switch, 38 psi on 40/60.
- **Check the pre-charge yearly.** Bladder tanks lose a little air over time.
- **Keep the tank out of direct sun** in an unvented well house. Heat shortens bladder life.

## Common mistakes

- Replacing a failed tank with the same undersized tank.
- Raising the pressure switch setting without resetting the tank pre-charge.
- Adding irrigation to a system sized for a house.

See [signs of a bad pressure tank](https://waterwelldrillingweatherford.com/learn/signs-of-a-bad-pressure-tank/), [pressure tank replacement cost](https://waterwelldrillingweatherford.com/learn/pressure-tank-replacement-cost/) and [well pressure tank replacement](https://waterwelldrillingweatherford.com/services/well-pressure-tank-replacement/).

## Bottom line

Find your pump's flow in gallons per minute, divide by about 0.3, and round up to the next standard tank size. Set the pre-charge 2 psi below the cut-in pressure. When in doubt, go bigger: an oversized tank costs a little more, while an undersized one costs you a pump.

Questions about your own well? Call [(817) 382-3840](tel:+18173823840). A person answers 24/7.

Sources

1. [Franklin Electric, Submersible Motors AIM manual (minimum run time)](https://www.geotechenv.com/Manuals/Franklin_AIM/Electric_Submersible_Motors_AIM.pdf)
2. [h2oguy.com, maximum starts for a Franklin Electric submersible motor](https://www.h2oguy.com/pumpsys/cyclecontrol.html)

## Quick answers

**Is a 20-gallon pressure tank big enough for a house?**

Usually not for a typical submersible well pump. A 20-gallon tank gives only about 5–6 gallons of drawdown, which is enough for a 1-minute run from a pump making about 5 gpm. Most household pumps make 8–12 gpm and need a larger tank.

**What is drawdown?**

Drawdown is the water the tank delivers between the pump turning off (cut-out) and turning back on (cut-in). It depends on tank size, pre-charge and switch settings, and it's roughly 25–30% of a tank's nominal size on common 30/50 and 40/60 settings.

**Do constant-pressure systems need a big tank?**

No. Variable-speed systems adjust pump speed to demand and typically use a small tank. Conventional on/off pumps are the ones that need proper drawdown.

## More well pressure tank replacement guides

- Urgent Help **[Why Is the Water Pressure Low on My Well?](https://waterwelldrillingweatherford.com/learn/low-water-pressure-on-a-well/).** Low pressure on a private well has a short list of causes. The pressure gauge and a few minutes of observation usually tell them apart.
- Cost Guide **[How Much Does Pressure Tank Replacement Cost?](https://waterwelldrillingweatherford.com/learn/pressure-tank-replacement-cost/).** 2026 prices to replace a well pressure tank, and why sizing it to the pump matters more than the tank's price.
- Urgent Help **[What Are the Signs of a Bad Well Pressure Tank?](https://waterwelldrillingweatherford.com/learn/signs-of-a-bad-pressure-tank/).** A failing pressure tank shows itself in the way the pump cycles, and a few simple checks confirm it before it takes the pump down with it.

[Well Pressure Tank Replacement service](https://waterwelldrillingweatherford.com/services/well-pressure-tank-replacement/)

## Ask about your property

Share the address area and what you're planning. We'll call back with the nearby well depths and a price range.

Faster by phone, any hour: [(817) 382-3840](tel:+18173823840)