Does copper or aluminum have less voltage drop?

Copper has about 61% of the resistance of aluminum, so it produces less voltage drop for the same wire gauge.

How does wire length affect voltage drop?

Voltage drop is directly proportional to wire length. Doubling the distance doubles the voltage drop.

WHOLE

CALCULATOR

Voltage Drop Calculator

Q: What is an acceptable voltage drop?

NEC recommends no more than 3% for branch circuits and 5% total for feeder plus branch combined.

Wire & Circuit Parameters

Wire Material

Copper

Wire Size

10 AWG

Source Voltage

Phase

AC Single Phase

Conductor Sets

1 set of conductors

Load Current (Amps)

One-Way Distance

Distance Unit

Feet

AWG Wire Resistance Reference (Copper)

AWG	Ω/1000ft	Ω/km
0000 (4/0)	0.04901	0.1608
000 (3/0)	0.0618	0.2028
00 (2/0)	0.07793	0.2557
0 (1/0)	0.09827	0.3224
1 AWG	0.1239	0.4065
2 AWG	0.1563	0.5128
3 AWG	0.197	0.6463
4 AWG	0.2485	0.8153
6 AWG	0.3951	1.2963
8 AWG	0.6282	2.0610
10 AWG	0.9989	3.2772
12 AWG	1.588	5.2100
14 AWG	2.525	8.2841
16 AWG	4.016	13.1759
18 AWG	6.385	20.9482

Voltage Drop Calculator: Estimate Wire Voltage Loss Accurately

Our Voltage Drop Calculator estimates the voltage drop across an electrical circuit based on wire material, wire size (AWG), conduit type, power factor, voltage, phase type, conductor configuration, distance, and load current. Excessive voltage drop can cause lights to flicker, heaters to underperform, and motors to burn out prematurely.

The calculator supports NEC data (resistance and reactance from the National Electrical Code), estimated resistance based on wire gauge, and custom impedance values. It handles both AC single-phase and three-phase circuits, as well as DC circuits.

According to the NEC, it is recommended that voltage drop should be less than 5% under a fully loaded condition. This can be achieved by selecting the correct wire size, minimizing run lengths, and being mindful of extension cord use.

Understanding Voltage Drop

When electrical current flows through a wire, it encounters resistance (or impedance in AC circuits). The voltage drop is the amount of electrical potential lost due to this resistance. Higher resistance, longer wire runs, and greater current all increase voltage drop.

There are four major causes of voltage drop: wire material (copper conducts better than aluminum), wire size (larger gauge = less drop), wire length (longer runs = more drop), and current load (more amps = more drop).

For AC circuits, impedance replaces simple resistance and includes both resistive and reactive components. The power factor (PF) describes the ratio of real power to apparent power and affects the voltage drop calculation in AC circuits.

How to Use the Voltage Drop Calculator

Step 1: Select Wire Material: Choose between copper and aluminum conductors.
Step 2: Select Wire Size: Choose the AWG gauge (e.g., 14 AWG for household, 3 AWG for heavy loads).
Step 3: Enter Voltage & Phase: Input the source voltage and select DC, AC single-phase, or AC three-phase.
Step 4: Enter Distance: Provide the one-way wire run length in feet or meters.
Step 5: Enter Load Current: Input the current draw in amperes.
Step 6: Calculate: View the voltage drop, percentage drop, and end voltage instantly.

Voltage Drop Formulas

DC / Single-Phase AC

Vdrop = 2 × I × R × L

Where I = current (A), R = resistance per unit length (Ω/ft or Ω/m), L = one-way distance. Factor of 2 accounts for the round-trip.

Three-Phase AC

Vdrop = √3 × I × R × L

For balanced three-phase systems, the √3 factor (~1.732) replaces the factor of 2.

Ohm's Law (basic)

Vdrop = I × R

The fundamental relationship: voltage drop equals current times total wire resistance.

AWG Wire Resistance Reference

AWG	Diameter (mm)	Area (mm²)	Cu Resistance (Ω/km)	Cu Resistance (Ω/1000ft)
4/0	11.684	107	0.1608	0.04901
2/0	9.266	67.4	0.2557	0.07793
1/0	8.252	53.5	0.3224	0.09827
4	5.189	21.2	0.8152	0.2485
8	3.264	8.37	2.061	0.6282
10	2.588	5.26	3.277	0.9989
12	2.053	3.31	5.211	1.588
14	1.628	2.08	8.286	2.525

Benefits of Our Voltage Drop Calculator

✓
NEC Compliant
Uses resistance data from the National Electrical Code for professional accuracy.
✓
All Circuit Types
Supports DC, AC single-phase, and AC three-phase calculations.
✓
AWG Reference Table
Built-in wire gauge reference with resistance values for quick lookup.
✓
Instant Results
Calculate voltage drop, percentage, and end voltage in real time.

Frequently Asked Questions

What is an acceptable voltage drop?

The NEC recommends no more than 3% for branch circuits and 5% for the total of feeder + branch circuit combined.

Does AC or DC have more voltage drop?

AC circuits may have slightly higher voltage drop due to reactance (inductive effects in the wire), but for most residential wiring the difference is small.