About

Sizing cables for Direct Current (DC) circuits requires strict adherence to voltage drop limits. Unlike AC, DC systems in automotive, marine, or solar (PV) applications often operate at lower voltages (12V, 24V, 48V), making them highly susceptible to resistive losses over distance. An undersized cable can lead to significant power loss (heat), equipment malfunction, or fire hazards.

This engineering tool calculates the minimum cross-sectional area required to keep voltage drop within a safe margin (typically 3% for critical loads). It considers the loop length (round trip), current load, and specific material resistivity (ρ) of Copper or Aluminum. Results provide both American Wire Gauge (AWG) and Metric (mm²) standards.

Formulas

The required cross-sectional area A is derived from Ohm's Law and the definition of resistance:

A = 2 ⋅ L ⋅ I ⋅ ρV_drop

Where:

L = One-way length of the cable (meters). Multiplied by 2 for the total circuit loop.
I = Current in Amperes.
ρ = Resistivity (0.0175 for Copper, 0.028 for Al).
V_drop = Allowable voltage drop (Source Voltage × Percentage).

Reference Data

AWG Size	Area (mm²)	Max Current (Ampacity)*	Resistance (Ω/km)
14 AWG	2.08	15 A	8.28
12 AWG	3.31	20 A	5.21
10 AWG	5.26	30 A	3.28
8 AWG	8.37	40 A	2.06
6 AWG	13.30	55 A	1.30
4 AWG	21.15	70 A	0.81
2 AWG	33.62	95 A	0.51
1/0 AWG	53.49	150 A	0.32
2/0 AWG	67.43	175 A	0.26

Frequently Asked Questions

In DC circuits, current must travel from the source to the load and back to the source to complete the circuit. Therefore, the total wire length affecting resistance is double the distance between the components.

For critical electronics or charging systems, a maximum drop of 3% is recommended. For non-critical loads (like general lighting), up to 10% may be acceptable, though 3% is the gold standard for efficiency.

Yes, but Aluminum has higher resistivity (approx 1.6x that of Copper). You will need a thicker gauge cable to carry the same current with the same voltage drop. Aluminum is often cheaper but requires careful termination to prevent oxidation.