Well pump size calculator: GPM from your fixture count, capped at the well's yield, with the pump type for your depth
Pump gpm = fixtures x 1 gpm (Water Systems Council, Red Lion): an 8-fixture house takes an 8 gpm pump, never above the well yield, submersible past 90 ft.
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Short answer
A well pump is sized in gallons per minute (gpm) by counting fixtures. The Water Systems Council’s rule, repeated in Red Lion’s selection guide and Nebraska’s worksheet, is that pump capacity in gpm should equal the number of fixtures in the home, at 1 gpm each. Red Lion’s worked example, one full bathroom (sink, tub or shower, toilet), kitchen sink, basement sink, outside faucet, washing machine and dishwasher, is 8 fixtures, so an 8 gpm pump. The second number is the well’s yield: the council’s general rule is never to install a pump with a greater capacity than the well, and to let a larger pressure tank carry a peak the well cannot. Pump type follows the pumping water level in Red Lion’s guide: a shallow-well jet to 25 ft, a convertible jet or submersible from 25 to 90 ft, a submersible from 90 to 250 ft. For the tank, Red Lion multiplies gpm by 3, so 8 gpm takes a 33 gal tank.
Skip this page if you are replacing a pump that worked: match the old nameplate, or go straight to the well pump review. The count below is for a new well, an added bathroom, or a pump that kept running dry.
Well pump gpm, pump type by depth, and the tank that goes with it
Pump gpm = fixtures x 1 gpm, a full bathroom counting 3 (Water Systems Council, Red Lion). The pump is capped at the well yield (Water Systems Council). Cross-check = outlets used at once x 3 gpm (Nebraska worksheet). Pump type from Red Lion's pumping-water-level bands; tank = next size above gpm x 3 on Red Lion's chart, drawdown at 30/50 psi.
What is the formula?
The Water Systems Council puts it in one sentence: “The capacity of the pump system in gallons per minute should equal the number of fixtures in the home”, with 12 fixtures or outlets giving a 12 gpm pump. Red Lion’s selection guide and step 1 of Nebraska’s worksheet use the same 1 gpm per outlet.
A fixture is any faucet, toilet or water-using appliance; Red Lion excludes water treatment equipment such as a water heater or filter.
| Variable | Value | Source |
|---|---|---|
| One fixture or outlet | 1 gpm | Water Systems Council; Red Lion; Nebraska worksheet |
| One full bathroom | 3 fixtures (sink, tub or shower, toilet) | Red Lion example |
| Outlets used at the same time | 3 gpm each | Nebraska worksheet, peak demand step |
| Pump capacity ceiling | the well’s yield in gpm | Water Systems Council |
| Pressure tank total volume | next size above pump gpm x 3 | Red Lion |
The Nebraska figure is a cross-check, not a second answer: when its outlets-at-once x 3 gpm lands above the fixture count, the pressure tank absorbs the peak.
What does a worked example look like?
Red Lion’s own house: one full bathroom, kitchen sink, basement sink, one outside faucet, washing machine and dishwasher.
- Fixtures: 3 + 1 + 1 + 1 + 1 + 1 = 8, so an 8 gpm pump.
- Cross-check: 2 outlets at once x 3 gpm = 6 gpm, under the count.
- Well yield 10 gpm on the driller’s report: 8 gpm stays under it. A 5 gpm well would cap the pump at 5 gpm.
- Pumping water level 100 ft: Red Lion’s 90 to 250 ft band, so a deep well submersible.
- Tank: 8 x 3 = 24 gal, next size up is 33 gal total volume, 10.3 gal drawdown at 30/50 psi.
Which pump type fits the depth?
The depth that matters is the pumping water level: the depth to water while the pump is running, usually deeper than the standing level, per Red Lion. A new well’s driller’s report prints it.
| Pumping water level | Pump type (Red Lion) | Well requirement |
|---|---|---|
| 0 to 25 ft | shallow-well jet pump, or convertible jet in single-pipe shallow configuration | 1-1/4 in suction pipe with foot valve |
| 25 to 90 ft | convertible jet pump in two-pipe deep configuration, or deep well submersible | 4 in well minimum |
| 90 to 250 ft | deep well submersible | 4 in well minimum |
| over 250 ft | call the maker | not covered by the guide |
Nebraska’s worksheet agrees on the shallow end: it lists a 25 ft maximum total lift for a shallow-well jet.
A pump that fits the depth but outruns the well is the common mistake, and the Water Systems Council’s rule forbids it; the symptom, a pump that cycles and then delivers air, is worked through on the well pump not working guide.
Which pressure tank goes with it?
Red Lion’s tank rule is pump gpm x 3, then the next largest tank. Drawdown is the water a tank delivers between pump starts; total volume is the shell.
| Red Lion tank | Total volume | Drawdown at 30/50 psi |
|---|---|---|
| RL14 | 14 gal | 4.3 gal |
| RL20 | 20 gal | 6.2 gal |
| RL33 | 33 gal | 10.3 gal |
| RL44 | 44 gal | 13.6 gal |
| RL81 | 81 gal | 25.1 gal |
| RL119 | 119 gal | 36.8 gal |
A bigger tank, per the Water Systems Council, covers a peak the well cannot and reduces pump cycling. Compare drawdown across brands on the well pressure tank review and the pressure tank cross-reference. The 30/50 and 40/60 figures are the pressure switch settings; Nebraska’s worksheet sets the tank’s air charge 2 psi below cut-on.
Only after the driller's report is in hand
The 8-fixture house above fits a 12 gpm class pump such as the Red Lion RL12G05-2W1V submersible, 1/2 hp, 2-wire, 115 V, 12 gpm , the model G of Red Lion’s own chart. Buy it only if the report shows the well yields at least 12 gpm; on a 5 gpm well it breaks the one rule on this page. The 1 hp RL12G10-2W2V, 230 V is the same family for a deeper pumping level. Full shortlist, jet pumps included, on the well pump review.
Where do the numbers come from?
- The 1 gpm per fixture rule and the yield ceiling: Water Systems Council, Sizing a Well Pump.
- The 8-fixture example, depth bands, well diameter, tank rule and drawdown chart: Red Lion, 1-2-3 Easy Guide to Pump & Tank Selection, read as a PDF copy hosted by InspectApedia; the maker’s own site does not link it.
- The 3 gpm per simultaneous outlet cross-check and the 25 ft shallow-jet lift: Nebraska’s water systems worksheet, which prints no agency name.
Red Lion’s pump chart (model letter by gpm and depth) is left off this page: the PDF text did not extract cleanly enough to copy. The pump’s gpm is only the supply side; the filter downstream has its own number on the whole-house filter flow rate calculator, and the well water whole-house filter review ranks units by it. A pump bought this autumn also goes on the well winter freeze checklist.
What owners buy for this
The top picks from Best well pump, jet and submersible: Red Lion and Goulds spec sheets sorted by depth to water, then GPM at a stated depth and pressure, because the depth picks the type before the horsepower, compared on published specs and certifications.
Depth to water 25 ft or less, one or two bathrooms, lowest tier
Red Lion RJS-50-PREM with M4 low-pressure cut-off switch (1/2 HP shallow jet, budget)
Red Lion catalog 996508: 1/2 HP, 115/230 V, 11.8 A at 115 V, 12.6 GPM at 5 ft lift and 30 psi, 6.2 GPM at 25 ft and 40 psi, 30/50 switch preset, 1-1/4 in intake, 1 in discharge; bundle adds a 30-50 psi M4 low-pressure cut-off switch
Depth to water 25 ft or less and the household demand of a typical family
Red Lion RJS-75-PREM (3/4 HP shallow jet, mid)
Red Lion catalog 996508: 3/4 HP, 115/230 V, 14.4 A at 115 V, 16.7 GPM at 5 ft lift and 30 psi, 7.2 GPM at 25 ft and 40 psi, 30/50 switch preset; catalog prints CSA certification to UL 778, CSA 108 and NSF/ANSI 372
Shallow well feeding a large house or irrigation that needs more than 10 GPM
Red Lion RJS-100-PREM (1 HP shallow jet, high flow)
Red Lion catalog 996508: 1 HP, 115/230 V, 17.6 A at 115 V, 23.2 GPM at 5 ft lift and 30 psi, 11.5 GPM at 25 ft and 40 psi, 30/50 switch preset, 3-year limited warranty per the RJS-PREM manual
Frequently asked questions
How many GPM well pump do I need for a 3-bedroom house?
Count fixtures, not bedrooms. The Water Systems Council rule is 1 gpm per fixture, so a house with two full bathrooms (6 fixtures), a kitchen sink, dishwasher, washing machine and one outside faucet is 10 fixtures and a 10 gpm pump. If the well driller's report shows a lower yield, the pump drops to the yield and a larger pressure tank carries the peak.
Can I install a 12 GPM pump on a 5 GPM well?
The Water Systems Council's general rule is never to install a pump with a greater capacity than the well. A pump that outruns the well pulls the water level down to the intake and runs dry. The council's answer to a peak above the yield is a larger pressure tank, which stores water between demands and also reduces pump cycling.
At what depth do I need a submersible instead of a jet pump?
Red Lion's selection guide uses the pumping water level, the depth to water while the pump runs. To 25 ft a shallow-well jet pump works; from 25 to 90 ft a convertible jet pump in its two-pipe deep configuration or a deep well submersible; from 90 to 250 ft only a deep well submersible. Past 250 ft Red Lion says to call its hotline.
What is the pumping water level and where do I find it?
It is the depth to water while the well is being pumped, and Red Lion notes it is usually deeper than the standing level with the pump off. For a new well it is on the well driller's report, which also lists the yield in gpm. An older well without a report needs a driller to measure both before a pump is sized.
Does the calculator size the pressure tank too?
It applies Red Lion's rule: multiply the pump's gpm by 3 and go to the next largest tank size, so an 8 gpm pump gets a 33 gal total-volume tank with 10.3 gal of drawdown at 30/50 psi. Drawdown, the water a tank actually delivers between pump starts, is the figure to compare across brands; the pressure tank review covers that.
Fact sheet and how to cite this page
- Answer
- Pump capacity in gpm equals the number of fixtures in the home at 1 gpm each, so Red Lion’s example house of 8 fixtures (one full bathroom, kitchen sink, basement sink, outside faucet, washing machine, dishwasher) takes an 8 gpm pump, a deep well submersible at a 100 ft pumping water level, and a 33 gal pressure tank from the gpm x 3 rule. The pump never exceeds the well’s own yield.
- Formula
pump gpm = total fixtures x 1 gpm (1 full bathroom = 3 fixtures), capped at the well yield in gpm; cross-check = outlets used at the same time x 3 gpm; tank total volume = next size above pump gpm x 3- Inputs
- Full bathrooms: 1
- Other indoor fixtures: 4
- Outside faucets: 1
- Outlets used at the same time: 2
- Well yield: 10 gpm
- Pumping water level: 100 ft
- Output
- 8 gpm pump (cross-check 6 gpm), under the 10 gpm well yield; deep well submersible for the 90 to 250 ft band; 33 gal tank with 10.3 gal drawdown at 30/50 psi
- Assumptions
- One fixture draws 1 gpm, the Water Systems Council rule repeated in Red Lion’s selection guide and the Nebraska water systems worksheet
- A full bathroom counts as 3 fixtures (sink, tub or shower, toilet), as in Red Lion’s example
- Water treatment appliances such as a water heater or filter are not fixtures, per Red Lion
- Depth bands are Red Lion’s: 0 to 25 ft shallow jet, 25 to 90 ft convertible jet or submersible, 90 to 250 ft submersible
- Method
- The calculator counts fixtures at 1 gpm each, caps the result at the well yield the reader enters, runs the Nebraska simultaneous-outlets x 3 gpm figure as a cross-check, picks the pump type from Red Lion’s pumping-water-level bands and the tank from Red Lion’s gpm x 3 rule and drawdown chart. Nothing was flow-tested; the figures are the published ones.
- Primary source
- Water Systems Council, Sizing a Well Pump (republished in The Driller, 1 November 2006) (manufacturer or vendor document)
- Facts verified
- Last updated
- Cite as
- OwnerSpec, "Well pump size calculator: GPM from your fixture count, capped at the well's yield, with the pump type for your depth", https://ownerspec.com/water/calculators/well-pump-size-gpm-calculator/, facts verified 11 October 2026.
Every figure above also appears, with its source, in the article. All sources ยท How OwnerSpec verifies numbers
Sources
- Water Systems Council, Sizing a Well Pump (republished in The Driller, 1 November 2006) (manufacturer or vendor document)
- Red Lion, 1-2-3 Easy Guide to Pump & Tank Selection, form 996245 (PDF copy hosted by InspectApedia) (manufacturer or vendor document)
- Nebraska (dwee.nebraska.gov), Water Systems Sizing and Selection worksheet (PDF) (government or regulatory source)