Engineering-Led Well Sizing · Watermain Supply · Houston, TX
Submersible Well Pump Sizing Calculator3 in and 4 in Wells · Home · Farm · Irrigation · Light Commercial
Tell it what the water is for, what the well looks like and where the water goes. It works out the flow, the total head, the pump size, the wiring, the pressure tank and every part that goes down the hole, then shows where to find each one.
5 to 80 GPMIn 3 in and 4 in Wells
1/2 to 10 HPSingle and Three-Phase
The Whole SystemPump, Tank, Wire, Controls
1-888.510.4036Talk to a Person
A submersible pump sits down in the well, below the water, and pushes water up the drop pipe to the house, the barn or the tank. Sizing one comes down to two numbers: how many gallons per minute you need at the busiest moment, and the total dynamic head — how many feet the pump has to lift and push that water, counting depth, elevation, pipe friction and pressure. This calculator works out both from things you can measure or count, then turns them into a pump size, a wiring choice, a tank, a pressure switch setting and a parts list. It covers homes, farms and ranches, irrigation and light commercial buildings on 3 in and 4 in wells, and flags anything bigger for a quote.
Print the result on one page, or send it to us from the results panel and we come back with the exact pump, stage count and a quote. Questions go to sales@watermainsupply.com or 1-888.510.4036. All products are genuine, factory-new equipment in original manufacturer packaging, sold and supported by Watermain Supply, an independent industrial supplier.
The Short Version
Peak flow: count the fixtures, the irrigation zone and the stock tanks; the busiest moment sets the GPM.
Pumping water level: static level plus drawdown. The pump lifts from there, not from the static level.
Total dynamic head: pumping level + elevation to the house + pipe friction + pressure × 2.31.
Flow class and HP: pick the GPM class that covers the flow, then the model that makes it at that head.
Wiring: 2-wire to 1-1/2 HP with no box; 3-wire with a control box to 5 HP; three-phase above that.
The rest: tank for at least a one-minute run, switch setting, pipe, wire, check valves, pitless, cap.
Submersible Pump Sizing Calculator
Fill in what you know; leave the rest at the defaults and change them later. It returns a duty and a class, not a model: the model and stage count come from the pump's own performance table, or from us.
Sizing received — thank youWe have your numbers and will come back with the pump, the controls and a quote. Anything urgent: 1-888.510.4036.
Step 1 · What the Water Is For
Drillers and pump installers: pick the second line
Your numbers
Optional; used for the well-yield check
House
Count what is plumbed. A full bath has a toilet, sink and tub or shower; a half bath has a toilet and sink.
Daily volume, 75 gal each
Light commercial, church, shop or barn
Each: one toilet and one sink
Wash bay, process, RV hookups
Irrigation
1 acre is 43,560 sq ft
1 in a week is typical turf
Livestock
Hot-weather planning figures: 30 gal a day per cow-calf pair, 20 per stocker, 15 per horse, 3 per sheep or goat.
Step 2 · The Well
The driller's log has most of these. The static level is the water level with the pump off for a few hours; drawdown is how far it falls while pumping.
Leave 30 if unknown
From a yield test; 0 if unknown
0 and we suggest one
Step 3 · Where the Water Goes
Elevation is from the wellhead up to the house or tank; enter a negative number if it is downhill.
Step 4 · Power
Look at the breaker that will feed the pump: a single-pole breaker is 115 V, a double-pole breaker is 230 V. Three-phase is usually only on commercial and ag services.
If nothing happens when you press the button, email the numbers to sales@watermainsupply.com and we will run them.
One letter page on our letterhead: your inputs, the results and the parts list. The detailed analysis below explains each figure.
Your Results
Design Flow—GPM
Total Dynamic Head—ft
Motor, Estimating—HP
Pump Setting—ft below grade
Pressure Tank—Gallons
What to Order
Item
What you need
Where to find it
Detailed Analysis
Demand
Flow
Where it comes from
Head term
Value
Where it comes from
Equipment
Value
How it is worked out
Method: house and building demand from water supply fixture units through a probability curve, the same estimating figures as our well and booster calculators; irrigation from area × inches ÷ watering time; livestock over the refill window. Head = pumping level + elevation + Hazen-Williams friction + pressure × 2.31. Motor size divides the water horsepower by a load ratio taken near the low end of Grundfos SP nominal duty points (0.45 at 5 GPM, 0.55 at 7 GPM, 0.60 to 12 GPM, 0.65 to 30 GPM, 0.55 above), so it leans to the larger motor; it is an estimate and the pump's performance table decides. A pump is allowed to run to 125 % of its nominal class. Flow classes, HP ceilings and voltages are those of the pumps we list.
Send This Sizing to Us
We pick the exact model and stage count on the manufacturer's curve, check the wire size on the motor's cable chart and come back with a quote. Your inputs and results go with the message.
How a Submersible Well System Works
Every part in the calculator's list, where it sits and what it does.
Static water level
Depth to water with the pump off for a few hours.
Drawdown and pumping level
While the pump runs the water falls. Static level plus drawdown is the pumping water level, the real lift.
Well yield
How many GPM the well gives up without running dry, from a yield test. The pump should not out-run it.
Setting depth
How deep the pump hangs: below the pumping level for submergence, and off the bottom to keep it out of the sediment.
Total dynamic head (TDH)
Everything the pump pushes against, in feet: lift + elevation + friction + pressure × 2.31.
Stages
A submersible stacks impellers. Each stage adds head at the same flow, so more stages means a deeper well or more pressure.
2-wire and 3-wire
The number of power conductors down the well, plus a ground. A 3-wire motor needs a control box at the surface for its start components; a 2-wire motor carries them inside.
Pitless adapter
The fitting that takes the water out through the side of the casing below the frost line, so the well cap stays sealed.
How the Calculator Sizes It
The same steps a pump installer runs, in order. Each result card and table comes from one of these.
1. Peak flow, not daily volume
A pressure system has to keep up with the busiest few minutes. Fixtures are counted as water supply fixture units and run through a probability curve, because not every tap opens at once: a house with 2 full baths, a half bath, a kitchen, a washer and two hose bibs comes to about 12 GPM. Irrigation and stock troughs add to it.
2. Pumping water level
Static level plus drawdown. A well at 120 ft that draws down 30 ft asks the pump to lift from 150 ft. Sizing on the static level is the most common reason a new pump comes up short.
3. Total dynamic head
Pumping level + elevation to the house + friction in the drop pipe and the service line + pressure × 2.31. It is worked out at the average of the switch, and the pump must also reach the cut-out pressure with the tap nearly closed or the switch never shuts it off.
4. Flow class, then HP
Submersibles are sold by nominal GPM: a 10 GPM pump, a 10S, a K series. A submersible can run to about 125 % of its nominal flow, so the calculator takes the smallest class at or above 80 % of your flow, then estimates the motor as GPM × TDH ÷ 3,960 ÷ a load ratio, rounded up to a standard size.
5. Wiring and power
The 115 V submersibles we list are all 1/2 HP. At 230 V, 2-wire motors run to 1-1/2 HP and 3-wire motors with a control box to 5 HP. Above 5 HP the 4 in motors we list are three-phase, fed from three-phase power or from a drive.
6. Tank, pipe, wire and fittings
The tank holds enough water for the pump to run at least a minute each start. Pipe is sized to stay at or below 5 ft/s and 3 ft of friction per 100 ft; drop pipe starts at 1-1/4 in. Check valves, the pitless, the cap, the torque arrestor and the cable run finish the list.
Five mistakes that cost a pumpSizing on the static level instead of the pumping level. Forgetting the elevation from the well up to the house. A pump that cannot reach the cut-out pressure, so it runs until it burns up. A tank too small, so the motor starts every few seconds. Wire too small for the distance, so the motor runs hot on low voltage.
2-Wire, 3-Wire, Three-Phase or Constant Pressure
How the pump is wired decides what goes on the wall, what it costs to service and how it handles the starts. The sizes are those of the pumps we list.
2-wire
3-wire
Three-phase
Constant pressure
Down the well
2 conductors + ground
3 conductors + ground
3 conductors + ground
Depends on the system
On the wall
Pressure switch only
Control box + pressure switch
Starter with overloads, or a drive
Drive or controller + transducer
Sizes we list
1/2 to 1-1/2 HP; 115 V at 1/2 HP only
1/2 to 5 HP, 230 V
To 7-1/2 HP at 230 V, 10 HP at 460 V in a 4 in motor
Grundfos SQE with CU 302; CUE 100 packages 1 to 3 HP; A.Y. McDonald AutoPAC and AutoDrive (2 to 5 HP)
Best for
Most homes: simple, nothing extra to buy
Larger single-phase pumps; start parts can be serviced without pulling the pump
Farms, irrigation and commercial with three-phase service
Steady pressure for showers and several users at once
Watch for
A failed start part means pulling the pump
The box must match the motor's brand, HP and voltage
Phase rotation and motor protection
Higher first cost; drive sized to the motor
Grundfos SQ and SQEThese 3 in pumps are 2-wire with the electronics built into the motor: soft start and protection against dry running and bad voltage, with no control box. The SQE adds constant pressure with the CU 302. Our SQ and SQE listings run to 1-1/2 HP, single-phase.
Pressure Tanks and Switch Settings
The tank lets the pump rest between starts. Too small and the motor cycles itself to death; the usable water in it, the drawdown, is what counts, not the size on the label.
Switch
Precharge
Drawdown factor
Tank per GPM, 1 min run
Typical use
30/50
28 PSI
0.30
3.4 gal
Single-story homes, older plumbing
40/60
38 PSI
0.26
3.9 gal
The common home setting
50/70
48 PSI
0.23
4.4 gal
Two-story homes, rotors, long runs
60/80
58 PSI
0.21
4.9 gal
Light commercial, uphill buildings
Drawdown factor from Boyle's law with the precharge 2 PSI below cut-in. The calculator uses a minimum run time of 1 minute below 2 HP and 2 minutes at 2 HP and up; the motor maker's manual gives its own minimum.
Worked exampleA 10 GPM pump on a 40/60 switch, 1-minute run: 10 gal of drawdown ÷ 0.26 = 39 gal of tank. On 30/50 the same pump needs 34 gal; on 50/70, 44 gal. The Pressure Tank Sizing Calculator works it out for any pump.
Worked Examples
Common jobs run through the calculator. The first is the default, so pressing Size It without changing anything reproduces it.
Worked example — a 2-bath house on a 4 in wellHouse: 2 full baths (2 × 3.6), a half bath (2.9), a kitchen sink (1.4), a washer (1.4) and 2 hose bibs (2.5 + 1.0) = 16.4 fixture units, which the demand curve turns into 11.8 GPM. Well: static level 120 ft + 30 ft of drawdown = a 150 ft pumping level. Head: 150 ft + 15 ft up to the house + 7.8 ft of friction in 180 ft of 1-1/4 in drop pipe and 150 ft of 1-1/4 in service line + 50 PSI (the middle of a 40/60 switch) × 2.31 = 288 ft. Pump: 11.8 GPM needs the 10 GPM class; 11.8 × 288 ÷ 3,960 ÷ 0.60 = 1.4, so about 1-1/2 HP, which can be 2-wire at 230 V. It must also reach 150 + 15 + 60 × 2.31 = 304 ft with the tap nearly closed, or the switch never shuts it off. Everything else: set at 180 ft (pumping level + 30 ft, 120 ft off the bottom of a 300 ft well); tank of at least 46 gal (11.8 gal of drawdown ÷ 0.26), precharged to 38 PSI; about 290 ft of cable, sized from the motor's cable chart.
Job
What was entered
Flow
TDH
Result
Ranch house and cattle
2 full baths, kitchen, washer, 3 hose bibs, 4 people; 60 cow-calf pairs and 4 horses; static 180 ft, drawdown 40 ft; 20 ft up, 300 ft run
14.6 GPM
375 ft
15 GPM class, about 3 HP, 3-wire with a control box; 114 gal tank
House plus lawn irrigation
3 full baths and a half bath; 20,000 sq ft of rotors, 1 in a week over 3 days, 4 h a day; 50/70 switch; static 80 ft
17.3 GPM
256 ft
15 GPM class, about 2 HP, 3-wire; 152 gal tank; irrigation governs
Church or small office
4 public restrooms, 2 kitchen sinks, a utility sink, 2 hose bibs; 6 in casing; static 150 ft; 60/80 switch
20.6 GPM
366 ft
20 GPM class, about 3 HP, 3-wire; 201 gal tank
Cabin on a 3 in well
1 bath, kitchen, hose bib, 2 people; 3 in casing, static 200 ft; 25 ft up; 30/50 switch
6.5 GPM
344 ft
Grundfos 10 SQ or 10 SQE, about 1-1/2 HP, 2-wire, no control box; 23 gal tank
Low-yield well to a cistern
4 people, 300 gal a day; well yields 3 GPM; fill a cistern over 12 h
0.4 GPM min
206 ft
5 GPM class, 1/2 HP on a float switch, with dry-run protection; a booster supplies the house
Irrigation, three-phase
60 GPM to a tank 800 ft away; 460 V three-phase; 6 in casing; static 100 ft, drawdown 40 ft
60 GPM
167 ft
60 GPM class, about 5 HP, three-phase starter; friction flagged at 16 % of the head
Results as the calculator returns them, rounded. Model and stage count are then read from the pump's performance table at that head.
What Each Kind of Job Usually Needs
Starting points only; your own numbers in the calculator decide.
Job
Typical flow
Typical setup
Worth knowing
Cabin or small home, 3 in well
5 to 10 GPM
Grundfos SQ, DAB S3; 2-wire; 30/50 or 40/60
SQ soft start and dry-run protection suit weak wells
Family home, 4 in well
8 to 12 GPM
10 GPM class, 3/4 to 1-1/2 HP, 2-wire or 3-wire, 40/60
Constant pressure is worth it for several showers at once
Large home, lawn on the same well
12 to 20 GPM
15 to 20 GPM class, 1-1/2 to 3 HP, 50/70
Run irrigation off-peak rather than size for both at once
Ranch: house plus stock tanks
10 to 20 GPM
10 to 20 GPM class; float valves on troughs
Remote tanks with no power are a job for the solar calculator
Acreage irrigation
20 to 80 GPM
25 to 80 GPM class, often three-phase
Match the pump to the largest zone, not the whole field
Church, shop, small office
15 to 35 GPM
60/80 switch or constant pressure
Public restrooms raise the peak more than floor area does
Low-yield well
At or below the yield
Small pump filling a cistern, booster to the house
Storage covers the peak so the well is never over-pumped
Installation Checklist
Everything that goes in, from the bottom up. The calculator's parts list sizes each one.
Pump and motor
Hang it below the pumping level and at least 10 ft off the bottom. In a casing larger than the motor, fit a flow sleeve so enough water passes the motor to cool it.
Check valves
One at the pump or within 25 ft above it, then about every 200 ft. A.Y. McDonald discharge heads carry one built in.
Drop pipe and torque arrestor
Sized for the flow. On plastic pipe, fit a torque arrestor above the pump and a stainless safety rope, and tape or tie the cable every 10 ft.
Cable and splice
Size the gauge from the motor's cable chart for the full run, panel to pump. Waterproof heat-shrink splice at the motor lead. Keep the ground.
Pitless adapter and cap
Pitless below the frost line, matched to casing and pipe; a sealed, vented well cap on top.
Tank, switch and protection
Tank precharged 2 PSI below cut-in with the tank empty; switch, gauge and a relief valve rated below the tank's maximum; a lightning arrestor; dry-run protection on a weak well.
Where to Buy: Pumps and Parts
The calculator points to these collections. Pick the flow class and HP it gave you, then the model from the performance table on the listing.
Grundfos
SQ and SQE 3 inSP 4 in 5S to 77SCUE 100
SQ and SQE for 3 in and 4 in wells: 5 to 30 GPM classes, 2-wire, 1/2 to 1-1/2 HP, soft start and built-in dry-run protection. SP for 4 in wells: 5S to 77S, 2-wire to 1-1/2 HP, 3-wire to 5 HP and three-phase to 10 HP. CUE 100 packages pair an SP pump with a constant-pressure drive.
Verdict: the SQ is the pick for a 3 in well or a weak well. For a single 3-wire SP job under 1-1/2 HP, note the small SA-SPM6 control boxes come in 10-packs; the 2-wire SP avoids the box.
Series J, V, K, L, P and M cover 5 to 25 GPM in 24000 and 23000 stainless, 26000 all-stainless, 21000 no-lead brass and 22000 and 25000 thermoplastic; the 24000 high-flow R, G, S, Q and T cover 35 to 80 GPM. 3-wire listings include the control box and three-phase listings the starter kit. AutoPAC packages and the AutoDrive give constant pressure.
Watermain Supply is an Authorized Stocking A.Y. McDonald and Baker Water Systems Distributor.
S4 stainless multi-impeller pumps for 4 in wells on the Tesla motor, 2-wire or 3-wire, 1/2 to 1-1/2 HP at 115 V or 230 V. S3 for 3 in wells, 5 to 15 GPM, two-wire stainless motor, sand resistant, to 1 HP. Tesla control boxes for the 3-wire motors.
Watermain Supply is an Authorized Stocking DAB Distributor.
If yours is not here, call. Sizing conversations are the part of this we are good at.
What size submersible pump do I need for my house?
Work out the peak flow from the fixtures and the total dynamic head from the well and the house. A house with 2 full baths, a half bath, a kitchen, a washer and 2 hose bibs peaks at about 12 GPM; on a well with a 150 ft pumping level, 15 ft below the house and a 40/60 switch, that is 288 ft of head and a 10 GPM-class pump of about 1-1/2 HP.
How do I work out total dynamic head for a well pump?
Add the pumping water level (static level plus drawdown), the elevation from the wellhead up to the house or tank, the friction in the drop pipe and the service line, and the pressure you want times 2.31. For a pressure switch, use the middle of the setting: 50 PSI on a 40/60 switch is 116 ft.
What is the difference between a 2-wire and a 3-wire well pump?
A 2-wire pump carries its start components inside the motor and needs only a pressure switch at the surface. A 3-wire pump keeps them in a control box on the wall, where they can be serviced without pulling the pump. In the pumps we list, 2-wire runs to 1-1/2 HP and 3-wire to 5 HP single-phase.
Do I need a control box for my submersible pump?
Only for a 3-wire single-phase motor, and it must match the motor brand, HP and voltage. A.Y. McDonald 3-wire listings include the control box. 2-wire pumps, including the Grundfos SQ and SQE, need none; three-phase motors use a starter or a drive instead.
What size pressure tank do I need for a well pump?
Enough drawdown for the pump to run at least a minute each start. A 10 GPM pump on a 40/60 switch needs 10 gal of drawdown, and with a drawdown factor of 0.26 that is a tank of about 39 gal total volume. Precharge it 2 PSI below the cut-in.
How deep should I set a submersible pump?
Below the pumping water level with room to spare, and at least 10 ft off the bottom. The calculator suggests the pumping level plus 30 ft, kept 15 ft off the bottom of the well.
What size wire do I need for a submersible pump?
The gauge comes from the motor maker's cable chart for its HP and voltage at the full length of the run: panel to wellhead, plus the setting depth, plus some slack. A 2-wire pump takes two conductors and a ground; 3-wire and three-phase take three and a ground.
Will a submersible pump fit a 3 in well?
Yes. The Grundfos SQ and SQE and the DAB S3 are built for 3 in wells and run to 30 GPM class and 1-1/2 HP. The 4 in pumps need a 4 in casing, and a well under 3 in usually takes a jet pump.
What if my well does not produce enough water?
Size the pump at or below the well yield, fit dry-run protection, and let storage carry the peaks: a small pump fills a cistern all day and a booster supplies the house. Enter the yield and choose Fill a tank or cistern to size it.
Is the calculator result a final selection?
No. It gives the duty, the flow class, an estimated HP and the parts list. The model and stage count come from the pump's performance table at your head, and the wire size from the motor's cable chart. Send the result from the results panel and we confirm it before you order.
Ready to Size It
Run the calculator and send the result, or send us the driller's log, the house and the power, and we come back with the pump, the controls, the parts list and a quote.
Watermain Supply · Houston, Texas · 1-888.510.4036 · sales@watermainsupply.com · Free shipping on orders of $500 and above
Technical data on this page is taken from manufacturer product literature and the pumps we list, and is subject to change by the manufacturer. Confirm against the current installation manual before specifying. Figures from the calculator are estimates, not a selection. Grundfos, SQ, SQE and CUE are trademarks of Grundfos Holding A/S. A.Y. McDonald, Baker, AutoPAC and AutoDrive are trademarks of A.Y. McDonald Mfg. Co. DAB, S3, S4 and Tesla are product names of DAB Pumps. Franklin Electric, Pumptec, Campbell and Monitor are trademarks of their respective owners. Used here for product identification only. Watermain Supply is a DBA of E4 Industrial LLC, an independent industrial supplier based in Houston, Texas.
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