Voltage drop
4.91 V
Free electrical performance calculator
Voltage Drop Calculator
Check voltage drop in volts and percent for copper or aluminum wire runs using current, circuit voltage, selected wire size, and one-way length.
Electrical performance check
Voltage drop inputs
Fixed wire size check
Circuit type
Conductor material
Quick examples
Voltage drop %
2.05%
Delivered voltage
235.09 V
Power loss
196.4 W
One-way run
125 ft
Resistance used
0.491 ohm / 1000 ft
Related planning calculators
Paint Calculator
Estimate paint needed by room size, coats, and surface coverage.
Concrete Calculator
Work out slab, footing, and column volume for concrete pours.
Room Size Calculator
Measure room dimensions, usable area, and layout planning totals.
Square Footage Calculator
Calculate total square footage for simple and multi-room plans.
Wire Size Calculator
Estimate minimum wire gauge from amp load, run length, conductor material, and voltage drop.
Framing Calculator
Estimate wall studs, plates, headers, opening framing, sheathing sheets, and waste allowance.
What is a voltage drop calculator?
A voltage drop calculator estimates how much voltage is lost as electrical current travels through a wire or cable. This tool uses your selected wire size, conductor material, circuit current, source voltage, and one-way run length to calculate the expected drop in both volts and percent.
It is useful when you already know the conductor size you plan to use and want to check whether the electrical performance is still acceptable. That makes it practical for branch circuits, feeders, workshop wiring, garage or outbuilding runs, low-voltage DC circuits, battery cable sizing, and basic solar wiring checks.
In real installations, excessive wire voltage drop can reduce equipment performance, cause dim lighting, create motor starting issues, and waste energy. A good cable voltage drop calculator helps you spot those issues early before you commit to a conductor size.
Why voltage drop matters in electrical design
Voltage drop matters because every conductor has resistance. As current moves through the wire, some of the source voltage is lost along the way. If the drop becomes too high, the equipment at the far end may receive less voltage than intended, which can affect how it runs.
This is especially important on long wire runs, high-current circuits, low-voltage systems, and motor loads. A small drop may be acceptable, but a large drop can lead to poor efficiency, weak performance, nuisance problems, or difficulty meeting good design practice.
Many electrical layouts aim for around 3% voltage drop on branch circuits as a practical design target, but the right limit still depends on the project, equipment sensitivity, wiring method, and local electrical code requirements. This tool is best used as a planning check before final verification.
Improves equipment performance
Keeping voltage drop under control helps lights, motors, electronics, and other loads operate more reliably.
Longer runs usually drop more voltage
As conductor length increases, resistance over the circuit path increases too.
Higher current increases drop
More current through the same wire size produces a greater voltage loss.
Undersized wire can cause issues
A conductor that is too small for the load and distance may produce excessive drop.
How voltage drop is calculated
Voltage drop depends on three main things: current, conductor resistance, and distance. The calculator uses practical resistance values per 1,000 feet for common copper wire and aluminum wire sizes, then applies the appropriate voltage drop relationship for the circuit type.
Resistance-based calculation
The tool uses wire resistance data and multiplies it by current and circuit path length.
Round-trip distance matters
For single-phase AC and DC circuits, current travels out and back, so the conductor path is effectively doubled.
Three-phase circuits use a different relationship
Three-phase voltage drop commonly uses the square root of 3 in the line-to-line formula.
Results are shown in volts and percent
That makes it easier to compare the drop against your design target or guideline.
Common voltage drop formulas
Single-phase AC or DC: Voltage Drop = 2 × Current × Resistance × Length
Three-phase AC: Voltage Drop = √3 × Current × Resistance × Length
Percent Voltage Drop: (Voltage Drop ÷ Source Voltage) × 100
The exact values can vary depending on conductor temperature, installation method, insulation type, and actual resistance under operating conditions. That is why this tool is best treated as a practical planning estimate rather than a final engineered design on its own.
Quick reference examples for voltage drop
These examples show how current, wire size, conductor material, and distance affect voltage drop. Exact values depend on the resistance data used by the calculator.
| Scenario | What usually happens |
|---|---|
| Long run + small wire | Higher voltage drop and higher percentage loss |
| Long run + larger wire | Lower voltage drop compared with smaller conductor sizes |
| Copper vs aluminum same size | Copper usually shows less drop because of lower resistance |
| Higher current same wire | Voltage drop increases as load current rises |
| Low-voltage DC circuits | Even modest drop can matter more because source voltage is already low |
How to use this voltage drop calculator
- 1
Select the conductor material
Choose copper or aluminum depending on the wire you plan to use.
- 2
Choose the wire size
Pick the conductor size you want to check for the circuit.
- 3
Enter current, voltage, and length
Add the circuit load current, source voltage, and one-way run length.
- 4
Review drop in volts and percent
Use the result to see whether the selected conductor size is likely acceptable.
Real-world applications, tradeoffs, and limitations
Branch circuits and feeders
Useful for checking whether a selected conductor size is reasonable over a given run length.
Solar, battery, and DC wiring
Helpful for low-voltage systems where even small losses can noticeably affect performance.
Copper and aluminum comparison
Lets you compare performance tradeoffs between lower-resistance copper and typically lower-cost aluminum.
Not a full code compliance check
Final conductor sizing still depends on temperature correction, conduit fill, ampacity, terminal ratings, and local code.
If the calculated voltage drop percentage is below your target, the wire size is usually reasonable from a performance standpoint. If the result is too high, you can often improve it by choosing a larger conductor, reducing current, shortening the run, or switching materials.
Copper and aluminum also deserve separate consideration. Copper wire has lower resistance at the same conductor size, so it usually produces less drop. Aluminum is often lighter and more economical, but it frequently needs a larger size to reach similar performance. This calculator helps you compare those tradeoffs before making a decision.
The result should still be verified against local electrical code, termination ratings, conductor temperature assumptions, ambient conditions, and installation details. This tool supports planning, but it does not replace final design review.
Frequently asked questions
- What causes voltage drop in a wire?
- Voltage drop is caused by conductor resistance combined with current and circuit length.
- Does one-way length or total length matter?
- Most calculators ask for one-way run length, then account for the round-trip path in single-phase AC and DC circuits.
- Is copper better than aluminum for voltage drop?
- At the same wire size, copper usually has lower resistance and therefore less voltage drop.
- What is a common voltage drop target?
- Many designs aim for around 3% on branch circuits, but acceptable limits depend on the equipment, application, and code guidance.
- Does this replace electrical code checks?
- No. It is a planning tool. Final design still needs verification for ampacity, temperature correction, conduit fill, and local code compliance.
Check wire voltage drop before you commit to a conductor size
Use this voltage drop calculator to estimate wire voltage loss in volts and percent for copper or aluminum conductors. It is a practical way to evaluate electrical wire sizing, compare conductor materials, and improve circuit performance before final installation.