# What size well pump do I need? > How a well pump is sized: static and pumping water levels, yield, pressure range and household demand, and why horsepower alone misleads. Read before you buy. URL: https://wellbornesuffolkwellpumprepair.com/guide/well-pump-sizing/ Learn Four measurements decide the right pump. The horsepower on the old motor is not one of them. The right well pump is set by the well's static water level, its pumping level and sustainable yield, the pressure range at the house, and the flow the household needs at peak. A pump matched to those runs efficiently and lasts; one chosen by horsepower alone either outruns the well or never reaches cut-out pressure. Key points - Measure the water levels and yield before choosing a pump. - Total lift includes depth to water, house elevation and the switch pressure. - A pump bigger than the well can feed draws the level down and cycles. - Tank and switch are sized with the pump, not afterwards. [Wellborne](https://wellbornesuffolkwellpumprepair.com/) sizes replacement pumps from measurements taken at the well, because the label on the old motor only tells you what someone chose last time, not what the well needs now. ## The four numbers that matter **Static water level.** Where the water stands in the well when the pump has been off for a while. It is the starting point for how far the pump has to lift. **Pumping water level.** Where the water settles while the pump runs. The difference between static and pumping level is the drawdown. A well with a small drawdown at a given flow has plenty of capacity; one with a large drawdown is working hard. **Sustainable yield.** How many gallons a minute the well can supply over time without the water falling to the pump intake. It is measured with a pumping test, ideally recorded when the well was drilled and checked again when the pump is out. **Pressure range and demand.** The [pressure switch](https://wellbornesuffolkwellpumprepair.com/pressure-switch-and-control-box-repair/)’s cut-in and cut-out, commonly 30/50 or 40/60 psi, and the flow the house needs when several fixtures run at once. ## Total lift: depth is only part of it A pump has to lift water from the pumping level to the surface, push it up to the house, overcome friction in the pipe, and still deliver the switch’s cut-out pressure. Each 2.31 feet of lift equals 1 psi, so delivering 60 psi at the house is like lifting the water almost 140 feet more. On a deep Suffolk well, where the Virginia Cooperative Extension clinic recorded an average reported depth of 371 feet, the pumping level can be hundreds of feet down before the pressure requirement is added. That total, called total dynamic head, is what the pump’s performance curve has to meet at the flow the house needs. ## Matching the pump to the well Pump manufacturers publish curves showing how much water each model delivers at each total head. The right pump delivers the household’s peak flow at the total head with some margin, but not more water than the well can sustain. Two mistakes are common: - **Oversizing.** A pump that outruns the well’s yield draws the water level down to the intake. It starts sucking air, sputters, cycles and wears quickly. [Sand](https://wellbornesuffolkwellpumprepair.com/guide/sand-and-sediment-in-well-water/) comes with it if the level falls near the screen. - **Undersizing.** A pump too weak for the head never reaches cut-out pressure, so it runs on and on, overheats and wastes power. The pump setting matters as much as its size. It has to sit below the lowest pumping level, with margin for dry summers and long declines in regional water levels, but far enough above the bottom of the well to avoid drawing sediment. ## Wire, tank and switch come with it Changing the pump can change everything around it. A larger motor may need heavier cable to avoid voltage drop over a long run. The [pressure tank](https://wellbornesuffolkwellpumprepair.com/pressure-tank-replacement/) has to hold enough water between cycles to give the new pump its minimum run time. The switch range has to be one the pump can reach at the well’s depth. Sizing the pump without the tank and switch is how a new pump [short-cycles](https://wellbornesuffolkwellpumprepair.com/guide/well-pump-short-cycling/) itself to an early end. ## When the well, not the pump, is the limit If the house’s peak demand is larger than the well’s sustainable yield, no pump fixes it. The choices are to spread demand out (irrigation at night, not with the laundry), add storage that the pump fills slowly and the house draws quickly, [rehabilitate](https://wellbornesuffolkwellpumprepair.com/well-rehabilitation/) a well whose screen has clogged, or add a second well. A [constant pressure system](https://wellbornesuffolkwellpumprepair.com/constant-pressure-well-pump-installation/) can help match pump output to demand, but it cannot make the well produce more. ## Where the numbers come from The well’s completion report, if one exists, records the depth, casing and the yield measured at drilling. The local health department holds records for wells from 1990 onward. Where there is no record, the levels and setting are measured when the pump is pulled. Keep those numbers: they make the next replacement simpler and show whether the well is changing over time. If you are not sure what your well needs, call [(757) 919-1972](tel:+17579191972) with whatever you know about the depth and the house, and we will tell you what has to be measured. Related service [Well pump replacement](https://wellbornesuffolkwellpumprepair.com/well-pump-replacement/) More guides - [Jet pump vs submersible](https://wellbornesuffolkwellpumprepair.com/guide/jet-pump-vs-submersible-pump/) - [Repair or replace a well pump](https://wellbornesuffolkwellpumprepair.com/guide/repair-or-replace-well-pump/) - [How Suffolk well systems work](https://wellbornesuffolkwellpumprepair.com/guide/suffolk-well-systems/) - [Why a well pump short cycles](https://wellbornesuffolkwellpumprepair.com/guide/well-pump-short-cycling/) - [How long well pumps last](https://wellbornesuffolkwellpumprepair.com/guide/how-long-do-well-pumps-last/) ## Questions people ask ### Is a 1 HP pump better than a 3/4 HP pump? Only if the well and the house need it. A larger pump on a well that cannot supply its flow will draw the water down and short-cycle. Horsepower follows from the lift and flow needed, not the other way round. ### How many gallons a minute does a house need? It depends on fixtures and habits. Count the fixtures likely to run at once at peak, such as a shower, a washing machine and a kitchen tap, and the flow each needs. Irrigation adds its own demand on top. ### Can the same pump serve the house and irrigation? It can if the well's yield and the pump's output cover both at the times they overlap. Often it is simpler to schedule irrigation for quiet hours or give it a separate shallow well.