What Size Well Pump Do I Need? HP Size Guide

Homeowners ask "what size well pump do I need" more than almost any other well question, and the answer matters more than most people realize. A pump that is too small will run constantly, deliver weak pressure, and burn out early. A pump that is too big will short cycle, waste electricity, and wear out its motor and pressure switch. Getting the size right is not about buying the biggest pump you can afford. It is about matching horsepower, flow rate, and well depth to your household demand. This guide walks through the three numbers you need and the simple steps to size a pump correctly.

Why Pump Size Matters

A well pump is rated by horsepower, but horsepower alone does not tell you how much water it delivers. What matters is the pump curve: how many gallons per minute the pump delivers at a given total lift, which is the vertical distance from the water level to the highest fixture plus friction losses in the piping. A 1 HP pump might deliver 15 gallons per minute at 50 feet of lift but only 7 gallons per minute at 200 feet. That is why two homes with the same pump can have very different results if their wells differ in depth.

Undersizing shows up as weak showers, a pump that never shuts off, and faucets that lose pressure when two fixtures run at once. Oversizing shows up as short cycling, where the pump starts and stops every few seconds because it fills the pressure tank too fast. Both problems shorten pump life and raise energy costs. Correct sizing gives steady pressure, reasonable run times, and a pump that lasts its full expected lifespan.

The Three Numbers You Need

Sizing a pump requires three pieces of information. First, the static water level: the depth from the surface to the water in the well when the pump is not running. This is more important than total well depth, because the pump lifts water from the water level, not from the bottom of the hole. Second, the peak flow rate your household needs, measured in gallons per minute, at the times of heaviest use. Third, the total lift, which adds the vertical lift to the pressure tank setting and friction losses, usually expressed as total dynamic head in feet.

You can find the static water level and well depth on your well completion report, or a contractor can measure them quickly. Peak demand you can estimate from your fixtures, as explained below. Total dynamic head is where a pump curve comes in: manufacturers publish curves showing flow at each head value, and you pick the pump whose curve meets your demand at your head. If this sounds technical, do not worry. The steps below turn it into a practical process, and our well pumps hub links to further guides for each pump type.

Step 1: Measure Well Depth and Water Level

Start with your well records. The driller's report lists total depth, casing diameter, static water level, and often the tested yield in gallons per minute. If you cannot find the report, your state water well database or local health department may have a copy. As a last resort, a well contractor can drop a sounder or weighted tape to measure the water level, usually for a modest service fee.

Note the difference between static level and pumping level. The pumping level is where the water drops to while the pump runs, and it is deeper than the static level. For sizing, use the pumping level if you know it, or add a safety margin of 10 to 20 feet to the static level. Also note the well yield: if your well produces only 6 gallons per minute, a 15 gallon per minute pump will suck the well dry and cycle on its low-water cutoff, if it has one. The pump must never exceed the well yield for sustained periods.

Step 2: Estimate Household Flow Rate

Peak demand is the flow your home needs when several fixtures run at once. A common rule of thumb is one gallon per minute per fixture that might run simultaneously, with standard fixture flows of about 2.5 gallons per minute for a shower, 2 gallons per minute for a bathroom faucet, 3 gallons per minute for a washing machine, and 2 gallons per minute for a dishwasher. A family of four with two bathrooms typically peaks around 8 to 12 gallons per minute during a busy morning.

Count generously rather than optimistically. If you water the garden while someone showers, or if you plan to add a bathroom or irrigation zone later, size for that future demand now, since replacing a pump later costs far more than buying one size up today. But do not overshoot wildly: sizing for 20 gallons per minute when your real peak is 8 will cause short cycling unless you also install a much larger pressure tank. The table below gives typical household targets.

Step 3: Match HP to Depth and Flow

With depth and demand in hand, use the pump manufacturer's curve or a sizing table to pick horsepower. As a rough guide for submersible pumps delivering about 10 gallons per minute: wells up to 100 feet deep usually need 1/2 HP, 100 to 200 feet need 3/4 to 1 HP, 200 to 300 feet need 1 to 1.5 HP, and deeper wells need 1.5 HP or more. For higher flow rates, shift up a size. For lower flow rates, shift down. Jet pumps follow a different scale because suction limits them to shallower wells; see our submersible vs jet pump comparison for the depth limits of each type.

When you are between sizes, it is usually better to choose the larger pump and pair it with an adequately sized pressure tank, rather than the smaller pump that will struggle at peak demand. A slightly oversized pump with a proper tank cycles normally, while an undersized pump runs hot and delivers weak pressure. If you are replacing a pump, check the old pump's rating plate, but do not blindly copy it: household demand, water level, and well yield may all have changed since it was installed. Our best well pumps of 2026 guide lists current models by horsepower class.

Common Sizing Mistakes to Avoid

The most common mistake is buying horsepower without checking the pump curve. Two 1 HP pumps can deliver very different flow rates at your depth, because one may be a 10 gallon per minute model and the other a 20 gallon per minute model. Always check the rated flow at your total lift, not just the horsepower on the box. The second mistake is ignoring well yield. A pump that outruns the well will draw down the water level, pull in air and sediment, and trip on low water or overheat.

The third mistake is forgetting friction loss. Long horizontal pipe runs, small diameter piping, and many elbows add friction that effectively increases the lift the pump must overcome. A system with 200 feet of horizontal run and several fittings may need a pump rated for 20 to 30 extra feet of head. The fourth mistake is sizing for average use instead of peak use. A pump that handles a single faucet fine but collapses when the shower and washing machine run together is undersized for real life. Size for the busiest hour, not the quietest.

Sizing the Pressure Tank to Match

The pressure tank is part of the sizing equation, not an afterthought. The tank's drawdown, the amount of water it delivers between pump cycles, should be large enough for the pump to run at least one minute per cycle. The rule is simple: drawdown in gallons should equal or exceed the pump flow rate in gallons per minute. A 10 gallon per minute pump needs at least 10 gallons of drawdown, which typically means a 30 to 40 gallon nominal tank, since only about a third of a tank's volume is usable drawdown.

If you upgrade pump size without upgrading the tank, short cycling is almost guaranteed. If your tank is old, check its air charge annually and replace it if the bladder has failed. A matched pump and tank pair is quieter, more efficient, and far longer lived than a mismatched set. When in doubt, a well contractor can size both in a single visit, often as part of a pump replacement quote.

When to Ask a Professional

Call a well contractor if you do not know your well depth, water level, or yield, if your well is deeper than 200 feet, if you need more than 15 gallons per minute, or if your current pump has chronic problems like short cycling or weak pressure despite correct-looking sizing. A contractor can run a yield test, measure levels accurately, and recommend a specific model from the pump curve rather than a generic table. That precision is worth the service fee on a purchase that should last 15 to 25 years.

Sizing a well pump is a one-time calculation that pays off every day the pump runs. Measure your water level, estimate your real peak demand, check the pump curve at your lift, and pair the pump with a properly sized tank. Get those four things right and you will have steady pressure, reasonable energy bills, and a pump that lasts. Questions about sizing for your specific well? Call (877) 762-1902 for guidance.