Submersible Pump Calculator
A comprehensive engineering tool to calculate submersible pump sizing, capacity, static head, dynamic head (TDH), stage counts, motor horsepower, well pump properties, cable gauge sizes, electrical power draws, and borehole performance.
Submersible Pump Sizing & Design Calculator
How to Size a Submersible Pump
Sizing a submersible pump correctly is critical to ensuring your water supply meets daily needs without overworking the pump motor. An incorrectly sized pump will cycle too frequently or fail to deliver appropriate pressure at the fixtures.
Follow this step-by-step engineering approach to size your system:
- 1Determine Flow Rate: Identify the peak water demand in Gallons Per Minute (GPM) or Liters Per Minute (LPM) based on house fixtures or irrigation needs.
- 2Calculate Total Dynamic Head: Measure static height differences and pipeline friction losses to establish the vertical head lift requirement.
- 3Verify Well Characteristics: Take note of static water level, drawdown level under pumping, and drop pipe diameters.
- 4Check Motor Cable Gauge: Use the electrical current draw and run lengths to verify voltage drop limits.
Pump Head Calculation
The pump head is the total vertical height a pump must push water against. Sizing for submersible borehole installations requires adding the depth to the pumping water level and the surface elevation rise, along with friction losses:
Friction losses scale quadratically relative to fluid velocity. Always use PVC or smooth plastic pipes where possible (C=150) to minimize pipeline resistance and head demand.
Pump Capacity Calculation
Pump capacity describes the volume of water the pump must deliver over a specific operational period. Domestic capacities are determined by household sizes or fixture fixture counts. In agricultural applications, it is defined by crop irrigation cycles:
Adding a safety margin ensures the well pump has enough recovery time and prevents constant motor switching that damages internal components.
Pump Stage Calculation
Submersible pumps utilize multi-stage impellers stacked vertically to increase pressure capacity. Because a single impeller stage has a physical limit on the head it can produce, stacking multiple stages increases head capabilities:
Operating a pump at the correct stage count guarantees it runs near its peak efficiency point, reducing electrical demands and motor wear.
Well Pump Sizing
Well pumps must be sized matching specific well water levels. Drawdown (or dynamic level) is the depth at which the water level stabilizes while pumping continuously. Sizing must be performed using the dynamic water level rather than static levels, as the water level drops significantly during high flow extraction.
Additionally, well depth, placement depth, and pressure tank requirements must be accounted for to ensure supply fixtures always receive consistent household pressure.
Pump Cable Size
Submersible cables run deep into boreholes and must carry electrical currents without dropping voltage below safety thresholds. Drop runs can be hundreds of feet, causing significant cable resistance:
Using copper wire is generally recommended for borehole cables to minimize diameter size, although aluminum remains a cost-effective option for long surface run runs.
Pump Horsepower
Motor horsepower measures the electrical and mechanical power needed to lift water. Sizing is split into hydraulic water horsepower (useful output) and shaft brake horsepower (actual motor rating):
Standard motor ratings exist in fixed intervals. Always size up to the next standard horsepower size to prevent motor overloads.
Engineering Formulas
Review the primary mathematical models used in our calculations:
- Hazen-Williams Friction Loss: h_f = 0.002083 × L × (100/C)^1.852 × Q^1.852 / d^4.8655
- Velocity Head Equation: h_v = v² / 2g
- Voltage Drop (Single Phase): VD = 2 × I × R × L / 1000
- Voltage Drop (Three Phase): VD = 1.732 × I × R × L / 1000
Worked Examples
Review these step-by-step sizing scenarios for well pumps and borehole cable calculations.
Example 1: Domestic Bore Well Pump
A home needs a submersible well pump supplying 15 GPM. The dynamic pumping water level is at 100 ft. Elevation to the discharge tank is 10 ft. Standard 50 PSI pressure tank is used. The drop pipe length is 120 ft of 1.25-inch PVC (C=150).
2. Pressure Tank Head equivalent = 50 PSI × 2.31 = 115.5 ft.
3. Pipe Friction loss = 1.6 ft (Hazen-Williams).
4. TDH = 110 + 115.5 + 1.6 = 227.1 ft.
5. BHP at 65% efficiency = (15 × 227.1) / (3960 × 0.65) = 1.32 HP.
6. Selection: 1.5 HP submersible pump.
Example 2: Agricultural Tube Well
An orchard irrigation well requires a pump delivery capacity of 100 GPM at 280 ft TDH. The pump has a stage efficiency of 72%. Head per stage is 35 ft.
2. BHP = (100 GPM × 280 ft) / (3960 × 0.72) = 9.8 HP.
3. Recommended Motor Size: 10 HP submersible motor.
Example 3: Industrial Borehole Pump
An industrial facility requires a borehole pump to supply 120,000 Gallons per day, operating 8 hours per day. Dynamic level is 180 ft.
2. With 20% margin for peak cycles: Recommended capacity = 300 GPM.
Example 4: Deep Well Pump
Sizing a deep aquifer well with a pumping level at 320 ft. The casing diameter is 6 inches. Sizing for 35 GPM flow rates.
2. Friction Loss over 350 ft pipe run = 2.4 ft.
3. Standard 40/60 tank = 50 PSI (115.5 ft head equivalent).
4. Total Head = 320 + 2.4 + 115.5 = 437.9 ft. BHP = 5.2 HP. Select: 7.5 HP motor.
Example 5: Cable Size Selection
Find the correct copper cable size for a 5 HP, 230V single-phase pump running 400 ft into a borehole. The allowable voltage drop limit is 3.0%.
2. Rated Current = 3730W / (230V × 0.85 PF) = 19.1 Amps.
3. Check #10 AWG: Resistance = 1.21 Ω per 1000 ft. Drop = 2 × 19.1 × (1.21 × 400/1000) = 18.5V (8.0% drop) - FAIL.
4. Check #6 AWG: Resistance = 0.491 Ω per 1000 ft. Drop = 2 × 19.1 × (0.491 × 400/1000) = 7.5V (3.2% drop) - FAIL.
5. Check #4 AWG: Resistance = 0.308 Ω per 1000 ft. Drop = 2 × 19.1 × (0.308 × 400/1000) = 4.7V (2.0% drop) - PASS.
Reference Tables
Use these engineering lookup charts for submersible motor sizing, cable gauges, and stage design parameters.
1. Standard Pump Capacities
| Application | Recommended Flow Capacity (GPM) | Typical Well Casing Size |
|---|---|---|
| Small Residential | 5 − 12 GPM | 4 inch |
| Large Residential / Farm | 15 − 30 GPM | 4 − 6 inch |
| Irrigation / Light Commercial | 35 − 80 GPM | 6 inch |
| Industrial / Municipal | 100 − 500 GPM | 8+ inch |
2. Typical Well Depths
| Aquifer Type | Standard Well Depth (ft) | Average Yield Range (GPM) |
|---|---|---|
| Shallow Sand / Gravel | 30 − 100 ft | 5 − 20 GPM |
| Standard Bedrock Aquifer | 100 − 300 ft | 10 − 50 GPM |
| Deep Aquifer Stratum | 300 − 1000 ft | 20 − 300 GPM |
3. Pump Head Loss (PVC Pipe Friction per 100 ft)
| Flow Rate (GPM) | 1" PVC (ft Head Loss) | 1.25" PVC (ft Head Loss) | 1.5" PVC (ft Head Loss) |
|---|---|---|---|
| 10 GPM | 3.2 ft | 0.8 ft | 0.4 ft |
| 20 GPM | 11.4 ft | 2.9 ft | 1.4 ft |
| 30 GPM | 23.8 ft | 6.1 ft | 2.9 ft |
| 50 GPM | 61.0 ft | 15.6 ft | 7.4 ft |
4. Pump Stage Table (Head Output vs Stage Count)
| Total Dynamic Head (ft) | Stages Needed (15 ft/stage) | Stages Needed (25 ft/stage) | Stages Needed (40 ft/stage) |
|---|---|---|---|
| 100 ft | 7 Stages | 4 Stages | 3 Stages |
| 200 ft | 14 Stages | 8 Stages | 5 Stages |
| 350 ft | 24 Stages | 14 Stages | 9 Stages |
| 500 ft | 34 Stages | 20 Stages | 13 Stages |
5. Motor HP Chart (Full Load Amps at 230V)
| Motor Rating (HP) | Single Phase FLA (Amps) | Three Phase FLA (Amps) | Typical Power Draw (kW) |
|---|---|---|---|
| 0.5 HP | 4.8 A | 2.0 A | 0.6 kW |
| 1.0 HP | 8.0 A | 3.6 A | 1.1 kW |
| 2.0 HP | 13.2 A | 6.2 A | 2.1 kW |
| 5.0 HP | 28.0 A | 15.2 A | 4.8 kW |
| 10.0 HP | 51.0 A | 28.0 A | 9.5 kW |
6. Cable Ampacity Table (75°C Copper vs Aluminum)
| Conductor Size (AWG) | Copper Ampacity (Amps) | Aluminum Ampacity (Amps) | Typical Conduit Fill Limit |
|---|---|---|---|
| #14 AWG | 15 A | - | 12 A |
| #12 AWG | 20 A | 15 A | 16 A |
| #10 AWG | 30 A | 25 A | 24 A |
| #8 AWG | 40 A | 30 A | 32 A |
| #6 AWG | 55 A | 40 A | 44 A |
| #4 AWG | 70 A | 55 A | 56 A |
7. Voltage Drop Table (Copper wire per 100 ft at 230V, Single-Ph)
| Load Current (Amps) | #12 AWG Drop (Volts) | #10 AWG Drop (Volts) | #8 AWG Drop (Volts) | #6 AWG Drop (Volts) |
|---|---|---|---|---|
| 10 Amps | 3.86 V (1.68%) | 2.42 V (1.05%) | 1.53 V (0.66%) | 0.98 V (0.43%) |
| 20 Amps | 7.72 V (3.36%) | 4.84 V (2.10%) | 3.06 V (1.33%) | 1.96 V (0.85%) |
| 30 Amps | - | 7.26 V (3.16%) | 4.58 V (1.99%) | 2.95 V (1.28%) |
| 50 Amps | - | - | 7.64 V (3.32%) | 4.91 V (2.13%) |
8. Flow Rate Conversion Table
| GPM (US) | LPM (L/min) | m³/hr (Cubic Meters) | LPS (L/sec) |
|---|---|---|---|
| 5 GPM | 18.9 LPM | 1.14 m³/hr | 0.32 L/s |
| 10 GPM | 37.9 LPM | 2.27 m³/hr | 0.63 L/s |
| 25 GPM | 94.6 LPM | 5.68 m³/hr | 1.58 L/s |
| 50 GPM | 189.3 LPM | 11.36 m³/hr | 3.15 L/s |
9. Pressure Conversion Table
| PSI (lb/in²) | Bar (Atmosphere) | Feet of Water Head (ft) | Meters of Water (m) |
|---|---|---|---|
| 20 PSI | 1.38 Bar | 46.2 ft Head | 14.1 m Head |
| 40 PSI | 2.76 Bar | 92.4 ft Head | 28.2 m Head |
| 60 PSI | 4.14 Bar | 138.6 ft Head | 42.2 m Head |
| 100 PSI | 6.89 Bar | 231.0 ft Head | 70.4 m Head |
Applications
Submersible pumps operate completely underwater and serve critical industries worldwide:
- Residential Bore Wells: Pushing drinking water up to household taps and pressure tanks.
- Agricultural Irrigation: Supplying water to field pivots, crops, and animal feeders.
- Industrial Water Supply: Drawing deep aquifer water for cooling towers or factory production.
- Municipal Water Systems: Distributing clean groundwater through city infrastructure.
Frequently Asked Questions
Determine your required GPM flow, compute the pumping water level drawdown depth, sum pipe friction head losses to get the Total Dynamic Head (TDH), and matching these parameters to the manufacturer's performance curve.
Divide the required Total Dynamic Head (TDH) by the head output generated per stage (impeller) as specified by the manufacturer's design charts, rounding up to the next integer.
Sizing requires identifying well depth, static water level, drawdown level under pumping, pipe length, drop pipe diameter, flow rates, and operating pressure limits (e.g. 30/50 or 40/60 PSI).
Take your total daily water consumption requirements, divide by the number of desired operating hours per day, and convert into GPM or LPM capacities, ensuring a safe sizing buffer.
Calculate motor full load amperage (FLA) using motor power, phase, and voltage. Reference wire resistance charts to ensure the conductor diameter limits voltage drop to under 3.0% over the cable's run length.
Install the pump casing at least 10 to 20 feet below the lowest dynamic (pumping) water level, but keep it at least 5 to 10 feet above the bottom of the well casing to prevent suctioning silt or sand.
