Wire Size Calculator – AWG & Voltage Drop | Electrical Wire Sizing

Wire Size Calculator

Determine wire gauge (AWG) based on current, length, material, and voltage drop

Current (amps)

Voltage (volts) (optional, for drop %)

Length (one‑way)

feet

meters

Material

Allowable voltage drop

volts

Temperature rating (°C)

Common Examples

Recommended Wire Size

Voltage Drop

Resistance

Ampacity

Wire Sizing Basics

VD = 2 × L × R × I / 1000

VD = voltage drop (volts)

L = one‑way length (feet or meters)

R = resistance per 1000 ft (or per km) at operating temperature

I = current (amps)

Standard ampacities per NEC table 310.16 (for reference).

Choose the smallest wire with ampacity ≥ current and voltage drop ≤ allowable.

People Also Ask

⚡ How do I choose the right wire size?

Consider current (ampacity), voltage drop, material, insulation temperature, and installation conditions.

📏 What is voltage drop and why does it matter?

Voltage drop is loss of voltage due to wire resistance. Excessive drop causes poor performance; typically limit to 3‑5%.

🔌 Does wire material (copper vs aluminum) affect size?

Yes, aluminum has higher resistance, so a larger gauge is needed for the same current and drop.

Wire Sizing Guide

Proper wire sizing ensures safety, efficiency, and code compliance. This calculator uses standard AWG wire properties and NEC ampacity tables (simplified). Always consult local codes for final installation.

Factors that influence wire size

Current (amps): Determines minimum ampacity.
Length: Longer runs require larger wire to limit voltage drop.
Material: Copper vs aluminum – different resistivity.
Temperature rating: Higher rated insulation allows higher current.
Installation: Conduit, ambient temperature, bundling derate ampacity.

AWG Copper Wire Properties (approximate)

AWG	Diameter (mm)	Resistance (Ω/1000ft @ 75°C)	Ampacity (75°C)
14	1.63	3.14	15
12	2.05	1.98	20
10	2.59	1.24	30
8	3.26	0.78	40
6	4.11	0.49	55
4	5.19	0.31	70
2	6.54	0.20	95

* Ampacity per NEC 310.16, copper, 75°C, not more than 3 current‑carrying conductors.

Frequently Asked Questions

Can I use this calculator for DC circuits?

Yes, voltage drop calculation is the same for AC and DC (ignoring reactance). For AC, power factor can affect voltage drop; this calculator assumes resistive load.

What is the difference between AWG and kcmil?

AWG (American Wire Gauge) is used for smaller wires up to about 4/0 (0000). Larger sizes are expressed in kcmil (thousand circular mils).