- Voltage Drop Calculator
Voltage Drop Calculator
Use our free voltage drop calculator to estimate electrical losses in DC, single-phase AC, and three-phase circuits. Compare copper AWG wire sizes, cable lengths, and voltage drop percentages to plan more efficient wiring.
- Free to use
- DC & AC Circuits
- AWG Comparison
Circuit & Wire Details
Estimate copper conductor voltage loss for DC and AC circuits.
Your Voltage Drop Result
Estimated conductor losses for your selected circuit.
A result within 3% or 5% is not proof of electrical code compliance. Verify conductor ampacity, insulation, temperature limits, protective devices and installation rules separately.
AWG Wire Size Comparison
Ten copper conductor sizes, compared at your chosen current, length and temperature.
| Wire size | Ω / 1,000 ft | Drop (V) | Drop (%) | Target |
|---|
Scroll horizontally on smaller screens. Resistance values are illustrative and can differ by conductor construction and manufacturer.
How to Use the Voltage Drop Calculator
Calculate estimated wire losses in three easy steps.
STEP 01
Enter Wire Details
Select your copper AWG wire size and enter the one-way cable length in feet or meters. Choose the conductor temperature for your calculation.
STEP 02
Set Circuit Values
Enter the load current and source voltage. Select DC, single-phase AC, or three-phase AC, then choose a 3% or 5% planning target.
STEP 03
Review Your Results
Check the calculated voltage loss, percentage drop, estimated load voltage, and cable power loss. Compare different conductor sizes in the AWG table.
Understanding Your Results
Learn what each calculation means for your electrical circuit.
Voltage Drop
Shows the estimated voltage lost through conductor resistance. Higher current, longer cable runs, and greater wire resistance increase this value.kW)
Percentage Voltage Drop
Displays voltage loss as a percentage of source voltage. Compare the result with your selected planning target to evaluate circuit efficiency.
Voltage at Load
Estimates the remaining voltage after subtracting conductor losses from the source voltage. Actual equipment voltage may differ under operating conditions.
Cable Power Loss
Estimates electrical power dissipated as heat in the conductors. It helps illustrate how wire resistance affects energy efficiency.
AWG Wire Size Recommendation
Identifies the thinnest wire in the calculator’s available AWG list that meets your selected voltage drop target. The comparison uses your cable length, circuit current, copper temperature, and supply voltage. Results also show wire resistance and voltage drop per 100 feet, making it easier to compare conductor options. This is a voltage-drop-only recommendation; you must check ampacity, insulation temperature limits, protection, and applicable electrical codes before selecting a cable.
How Voltage Drop Is Calculated
Voltage drop occurs when electrical current passes through a conductor with resistance. The amount of loss depends on wire size, cable distance, current, and conductor temperature.
Our calculator uses approximate copper resistance values for a simplified electrical voltage drop calculation.
DC Voltage Drop Formula
Voltage Drop (V) = 2 × Length (ft) × Current (A) × Resistance (Ω/1,000 ft) ÷ 1,000
The factor of two accounts for the outgoing and returning conductors.
Single-Phase AC Formula
Voltage Drop (V) ≈ 2 × Length × Current × Resistance ÷ 1,000
Three-Phase AC Formula
Voltage Drop (V) ≈ √3 × Length × Current × Resistance ÷ 1,000
For three-phase systems, enter the line-to-line source voltage.
These AC formulas are resistance-only approximations. They do not account for cable reactance, power factor, or harmonics.
Voltage Drop Percentage
Voltage Drop (%) = Voltage Drop ÷ Source Voltage × 100
Practical Example
Consider a 48V DC electrical circuit with these values:
Wire size: 10 AWG copper
One-way cable length: 100 ft
Load current: 20 A
Conductor temperature: 75°C
Planning target: 3%
The calculator estimates:
Voltage drop: 4.860 V
Voltage drop percentage: 10.12%
Estimated load voltage: 43.140 V
This exceeds the selected 3% planning target. In the tool’s available comparison, 4 AWG is the thinnest listed conductor that meets the target under these assumptions.
Cable Length: Longer wires have more total resistance. Increasing the one-way conductor distance increases voltage loss when the current, wire size, and other conditions remain unchanged.
Wire Gauge: Larger copper conductors generally have lower resistance. In the AWG system, lower gauge numbers indicate thicker wires, while sizes such as 1/0 and 2/0 are larger still.
Electrical Current: Higher current increases voltage drop across the same conductor. Current also affects resistive heating, making proper wire sizing important for both efficiency and electrical safety.
Conductor Temperature: Copper resistance increases as its temperature rises. This calculator provides approximate resistance estimates at 20°C and 75°C to help illustrate temperature-related differences.
How Wire Size Affects Voltage Drop
Compare conductor losses using these five simple steps.
1. Select Wire Size
Choose copper conductor gauge from available sizes.
2. Enter Cable Length
Measure the one-way distance of your circuit.
3. Add Electrical Load
Enter the expected current and source voltage.
4. Select Circuit Type
Choose DC or the appropriate AC circuit.
5. Compare Losses
Review voltage drop percentages.
Frequently Asked Questions
How do I calculate voltage drop in a wire?
Multiply conductor resistance by current and effective circuit length. For a DC circuit with separate supply and return conductors, the simplified calculation uses twice the one-way distance.
What is an acceptable voltage drop percentage?
A commonly used design recommendation is approximately 3% for a branch circuit and 5% combined across feeder and branch circuits. These are general efficiency guidelines, not universal mandatory limits. Always check applicable standards and equipment requirements.
Does thicker wire reduce voltage drop?
Yes. Thicker copper wire generally has lower electrical resistance, which reduces voltage loss when current and cable distance remain the same.
What is the difference between DC and AC voltage drop?
DC voltage drop can be estimated using conductor resistance and current. AC circuits can also be affected by reactance and power factor. This calculator provides simplified resistance-only estimates for both.
Can I use this calculator for solar panel wiring?
Yes, it can estimate resistive voltage losses in solar DC cable runs, battery connections, and other electrical circuits. It does not perform complete PV conductor sizing or safety checks.
Why does a 12V system have a higher percentage voltage drop?
The same absolute voltage loss represents a larger percentage of a lower supply voltage. For example, losing 1V in a 12V circuit is a larger percentage than losing 1V in a 48V circuit.
Does this calculator check wire ampacity?
No. The AWG recommendation only considers the selected voltage-drop target. For comprehensive wire-sizing calculations that also consider current-carrying capacity, consult the Southwire Voltage Drop Calculator or a qualified electrical professional.
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Important: This voltage drop calculator provides approximate conductor resistance calculations only. It does not verify wire ampacity, electrical codes, fault protection, insulation ratings, AC impedance, or the safety of a specific installation. Consult a qualified electrician for final wiring decisions.