Pump size depends on your household's peak water demand and how deep your well is

A well pump must be large enough to deliver water when you need it most — typically in the morning when multiple people shower, do laundry, and fill coffee makers at once. If the pump is too small, you'll run out of pressure or water mid-shower. If it's oversized, you waste electricity and money. Sizing correctly means measuring two things: how much water your household uses at peak times (flow rate, measured in gallons per minute) and how far the pump must push that water (head, measured in feet).

Most residential wells use either a submersible pump (sits inside the well) or a jet pump (sits above ground). The sizing math is the same for both, but submersible pumps are more common in deep wells and jet pumps in shallow ones. You'll need to know your well depth, the number of people in your home, and what fixtures you plan to run at the same time.

Key Takeaways

  • Peak household demand is usually 3 to 5 gallons per minute per person, so a family of four typically needs a pump rated for 12 to 20 gallons per minute.
  • Total head is the well depth plus the distance from the well to your house plus pressure tank height, and it determines how much power the pump needs.
  • A pressure tank stores water so the pump doesn't run constantly; tank size should be roughly one-third of your peak hourly demand in gallons.
  • If your well is deeper than 25 feet, a submersible pump is almost always the right choice; shallower wells can use jet pumps.
  • A licensed well contractor can measure your well depth and test your water recovery rate, which is the most reliable way to size correctly.

Calculate your household's peak water demand

Start by estimating how much water flows through your home when multiple fixtures run at once. Each fixture has a standard flow rate: a shower uses about 2.5 gallons per minute, a toilet fill about 3 gallons per minute, a kitchen sink about 2 gallons per minute, and a washing machine about 2 gallons per minute. If you run a shower and a toilet at the same time, that's 5.5 gallons per minute.

A simpler approach: multiply the number of people in your household by 3 to 5 gallons per minute. A family of four needs a pump rated for 12 to 20 gallons per minute. If you have a large lawn you plan to irrigate or a hot tub, add 5 to 10 gallons per minute for those uses. This gives you your required flow rate.

Write down this number — you'll need it when you talk to a pump supplier or contractor. If you're unsure whether your estimate is realistic, ask a well contractor to measure your well's recovery rate, which is how fast water refills in the well after you've drawn some out. A well that recovers 5 gallons per minute can't support a pump rated for 15 gallons per minute, no matter how much you need it.

Measure the total head your pump must overcome

Head is the total vertical distance the pump must push water, measured in feet. It includes three parts: the depth of your well, the elevation gain from the well to your house, and the pressure needed in your tank. Add these together to get your total head.

Start with well depth. If you don't know it, a well contractor can measure it with a weighted tape or electronic probe — this usually costs $50 to $150. If you have your well drilling report, the depth is listed there. Next, measure the elevation gain: if your well is 100 feet from your house and the house is 20 feet higher than the well, that's 20 feet of elevation gain. Finally, add 20 to 30 feet for pressure tank operation — the pump must push hard enough to fill the tank and maintain pressure when the tank is full.

Example: a well 80 feet deep, 50 feet away with 15 feet of elevation gain, plus 25 feet for tank pressure, equals 170 feet of total head. This number tells the pump supplier what size motor you need. A pump that can deliver 15 gallons per minute at 50 feet of head is much smaller and cheaper than one that delivers 15 gallons per minute at 200 feet of head.

Choose between submersible and jet pump types

A submersible pump sits underwater inside the well casing and pushes water up through a pipe to your house. It works at any depth and is the standard choice for wells deeper than 25 feet. Submersible pumps are reliable, quiet, and don't need a separate above-ground installation. They cost more upfront but last 10 to 15 years with minimal maintenance.

A jet pump sits above ground, usually in a basement or pump house, and uses suction to pull water from the well. Jet pumps work only on shallow wells — typically 25 feet deep or less — because suction has a physical limit. They're cheaper to buy and easier to repair, but they're louder and less efficient. If your well is deeper than 25 feet, a jet pump won't work.

If your well depth is between 20 and 30 feet, ask a contractor which type makes sense for your specific well. Some shallow wells have low recovery rates that favor a submersible pump even though a jet pump could technically work.

Size your pressure tank to match your pump

A pressure tank stores water under pressure so your pump doesn't run every time you turn on a faucet. Without one, the pump would start and stop dozens of times a day, wearing out quickly. Tank size should be roughly one-third of your peak hourly demand in gallons.

If your pump delivers 15 gallons per minute and you want it to run for at least 2 minutes before the pressure drops and it starts again, you need a tank that holds about 30 gallons (15 gallons per minute × 2 minutes). A 30 to 40 gallon tank is typical for a household of four. Larger tanks (50 to 80 gallons) reduce how often the pump runs, which saves electricity and extends pump life, but they cost more and take up space.

The tank itself has an air charge — a pocket of compressed air that pushes back on the water. When you buy a tank, the air charge is usually set to about 2 pounds per square inch (psi) below your pump's cut-in pressure. A contractor can adjust this if needed. If the air charge is wrong, the tank won't work efficiently and the pump will cycle too often.

Account for water quality and special conditions

If your water is sandy or contains sediment, you may need a larger pump or a different type to avoid clogging. Sand in the well can damage a pump's internal parts, so some contractors recommend a pump with a larger intake screen or a submersible model that can handle grit better. A water test will show whether sediment is a concern.

If your water is very hard (high in minerals) or acidic, the pump itself isn't affected, but your pipes and fixtures will corrode faster. This doesn't change pump sizing, but it's worth knowing because you may want to install a water softener or pH adjustment system downstream of the pump. These systems add a small amount of back-pressure, so mention them to your contractor when sizing.

Cold climates require special attention to frost protection. If your pump house or above-ground pipes are exposed to freezing, you'll need insulation, heat tape, or a drain-down system. This doesn't change pump size, but it affects where you can install the pump and pressure tank.

Work with a well contractor to confirm your sizing

Once you've estimated your flow rate and total head, contact a licensed well contractor in your area. Bring your well depth (or ask them to measure it), your household size, and a list of any large water uses you plan to add. They can test your well's recovery rate, which is the most important number you can't calculate yourself.

A contractor will also check your existing pressure tank (if you have one) to see if it's the right size and whether the air charge is correct. If you're replacing an old pump, they can often reuse the tank if it's in good condition. If you're installing a new well, they'll size everything from scratch and handle the electrical hookup, which must meet local code.

Most well contractors charge $100 to $300 for a site visit and sizing consultation. This is money well spent because an undersized pump will frustrate you for years, and an oversized one will waste electricity. The contractor can also tell you whether your well is reliable enough to support the pump size you want — some wells have low recovery rates that limit your options.

Frequently Asked Questions

What if my well is very deep — say, 300 feet?

A deep well needs a submersible pump with a larger motor to overcome the extra head. Your total head will be around 330 to 350 feet (well depth plus elevation and tank pressure), so the pump must be sized for that. Deep wells also tend to have lower recovery rates, so your flow rate may be limited. A contractor can test your well's recovery rate and recommend a pump that won't overdraw it.

Can I use a bigger pump than I need to fill my tank faster?

No. An oversized pump will overdraw your well, pulling water faster than it refills. This can damage the pump (it will run dry or cavitate) and lower your water table. Size the pump to match your well's recovery rate, not your impatience. If you want faster fill times, install a larger pressure tank instead — it stores more water so the pump runs less often but longer.

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

The pump should run for at least 1 to 2 minutes before the pressure drops enough to trigger a restart. If it's cycling on and off every 30 seconds, your tank is too small or the air charge is wrong. A contractor can test the air charge with a tire gauge and adjust it if needed. If the tank is too small, you'll need to replace it.

What's the difference between a 1 horsepower and a 2 horsepower pump?

Horsepower (hp) is the motor's power output, which determines how much flow and head the pump can deliver. A 1 hp pump typically delivers 10 to 15 gallons per minute at moderate head; a 2 hp pump delivers 15 to 25 gallons per minute. The right size depends on your flow rate and total head — a contractor can match the horsepower to your specific well and household needs.

Do I need a backup pump or generator?

A backup pump or generator is optional but useful if you live in an area with frequent power outages. A generator can keep your pump running during an outage so you still have water. A backup pump (usually a smaller jet pump) can provide basic water pressure if your main pump fails. These are nice-to-have upgrades, not requirements for sizing your primary pump.