01
The purpose
What does this calculator estimate?
How much voltage your wire run loses — in volts and percent — and whether it's within safe limits.
Electrical · H3
Pool Circuit Voltage Drop Calculator
How much voltage your wire run loses — in volts and percent — and whether it's within safe limits.
Measure the inputsKeep voltage drop at or under 3% for healthy motor performance.
Read the full resultOver 5% drop is unacceptable — upsize the wire or shorten the run.
Check the boundaryAluminum drops more voltage than copper at the same gauge.
Useful forElectricalPlanningComparisonVerification
Live calculation
Voltage drop inputs
✓ Checked May 2026
Enter wire gauge, length, load, and material.
Calculated result
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Enter the required values to calculate.
Enter the known values. Let the engine handle the calculation.
✓ Formula checked↻ Live result○ No account needed
Planning estimate only. Confirm product labels, equipment specifications, qualified-professional advice and local requirements before acting.
The result, explained
Use the Pool Circuit Voltage Drop Calculator result with context.
How much voltage your wire run loses — in volts and percent — and whether it's within safe limits.
02
The tool
What information does it use?
- Wire gauge: AWG of the installed conductor.
- Run length (one-way): enter a measured or verified value
- Load amps: Actual running current.
- Voltage: 115V or 230V.
- Conductor: Copper or aluminum.
03
The method
How to use this calculator
- Wire gaugeAWG of the installed conductor.
- Run length (one-way)Enter the value you can verify.
- Load ampsActual running current.
- Voltage115V or 230V.
- ConductorCopper or aluminum.
04
The relationship
The formula in plain English
Voltage drop = (2 × K × amps × length) ÷ circular mils
K = 12.9 copper, 21.2 aluminum. ≤3% is good, >5% unacceptable. Drop % = drop ÷ voltage.05
Worked through
A worked example: #10 copper, 100 ft, 20 A, 230V
- CM for #10 = 10,380
- Drop = (2 × 12.9 × 20 × 100) ÷ 10,380 = 4.97 V
- % = 4.97 ÷ 230 = 2.16% → compliant
| Length | #12 | #10 | #8 | #6 |
|---|---|---|---|---|
| 50 ft | 1.7% | 1.1% | 0.7% | 0.4% |
| 100 ft | 3.4% | 2.1% | 1.3% | 0.8% |
| 150 ft | 5.1% | 3.2% | 2.0% | 1.3% |
| 200 ft | 6.8% | 4.3% | 2.7% | 1.7% |
06
Why it matters
How the result supports the next decision
Keep voltage drop at or under 3% for healthy motor performance.
Over 5% drop is unacceptable — upsize the wire or shorten the run.
07
Good inputs
Improve the estimate before relying on it
- Keep voltage drop at or under 3% for healthy motor performance.
- Over 5% drop is unacceptable — upsize the wire or shorten the run.
- Aluminum drops more voltage than copper at the same gauge.
- Voltage drop is doubled because current travels out and back (the '2' in the formula).
- Low voltage at the motor causes overheating and early failure.
08
The boundary
How to interpret the result
Use this as a planning reference only; a licensed electrician and local code determine the installation.
The engine reports invalid inputs and safety warnings beside the result. Resolve those messages before using the estimate.
09
Before acting
What should override this estimate?
- Measured site conditions and current test results
- Product labels and manufacturer specifications
- Qualified-professional advice and applicable local codes
10
Common questions
Frequently asked questions
How do I calculate voltage drop?
Multiply two times the conductor constant (12.9 for copper, 21.2 for aluminum) by the load amps and the one-way run length, then divide by the wire's circular-mil area. That gives the drop in volts; dividing by the system voltage and multiplying by 100 gives the percentage. The factor of two accounts for current traveling out and back.
What is an acceptable voltage drop?
Three percent or less on a branch circuit is the widely accepted target for good performance. Up to five percent is generally tolerable, but beyond that is unacceptable because the equipment receives too little voltage. For pool pumps and heaters, staying at or under three percent protects motor life.
Why does voltage drop matter for pool motors?
Motors are sensitive to supply voltage. When voltage drop is excessive, the motor draws more current to do the same work, runs hotter, loses torque, and wears out faster. Keeping the drop within limits ensures the pump and other equipment get the voltage they're designed for and last their full life.
Does aluminum wire have more voltage drop?
Yes. Aluminum's higher resistance constant (about 21.2 versus copper's 12.9) means more voltage drop at the same gauge, length, and load. To match copper's performance, aluminum must be a larger gauge. That's one reason copper is favored for pool equipment runs despite its higher material cost.
How do I reduce voltage drop?
Use a larger wire gauge, shorten the run if possible, or use copper instead of aluminum. Upsizing the conductor is the most common fix — each step up in gauge has more circular-mil area and less resistance, cutting the drop. The wire-gauge calculator sizes the conductor to your target drop directly.
What is acceptable voltage drop for a pool pump?
3% or less is the target; over 5% is unacceptable and requires heavier wire.
How do you calculate voltage drop?
(2 × K × amps × length) ÷ circular mils, where K is 12.9 copper or 21.2 aluminum.
What causes voltage drop?
Wire resistance over distance — longer runs, smaller gauge, higher current, and aluminum all increase it.
Primary sources
Use the result with current guidance.
These official references support safe planning context. Product labels, local requirements and qualified-professional advice take priority over a general calculator estimate.