12 Volt - Maximum Wire Length vs. Current

Maximum wire length calculator for 12 volt copper conductor systems. Calculate the maximum length of copper wires based on current, cross-sectional area, and acceptable voltage drop for typical electrical circuits and automotive applications.

Maximum Wire Length Calculator

This calculator determines the maximum length of copper wires for 12 volt systems based on current, wire cross-sectional area, and voltage drop constraints.

Important Notes:

For typical electrical circuits with two wires (back and forth), the calculated length is the total wire length. The maximum distance between source and equipment is half the calculated distance.
In automotive applications where equipment is grounded to the chassis, the maximum distance equals the calculated length.
Formula: L = U / (R × I), where U is voltage drop, R is resistance per meter, and I is current.

Calculator

Inputs

Voltage (volts)

Current (amps)

Cross Sectional Area (mm²)

Voltage Drop (%)

Results

Voltage Drop-- volts

Resistance per Meter (Copper)-- ohm/m

Maximum Wire Length (Total)-- meters

Maximum Wire Length (Total)-- feet

Maximum Distance (Single Direction)-- meters

Maximum Distance (Single Direction)-- feet

Current (A)	Wire 5.26 mm² (m)	Wire 8.37 mm² (m)	Wire 13.3 mm² (m)	Wire 26.7 mm² (m)	Wire 33.6 mm² (m)
2	19.3	30.7	48.8	97.5	123
4	9.7	15.3	24.4	48.8	61.5
6	6.4	10.2	16.3	32.5	41
8	4.8	7.7	12.2	24.4	30.8
10	3.9	6.1	9.8	19.5	24.6
15	2.6	4.1	6.5	13	16.4
20	1.9	3.1	4.9	9.8	12.3
25	1.6	2.4	3.9	7.8	9.8
30	1.3	2	3.3	6.5	8.2

Reference Information

Copper Resistivity Data:

Resistivity of copper at 20°C: 0.01754 ohm·mm²/m

Wire Gauge Reference:

#2 (33.6 mm²)
#4 (26.7 mm²)
#6 (13.3 mm²)
#8 (8.37 mm²)
#10 (5.26 mm²)

Scaling Factors:

Double the distance if 4% voltage drop is acceptable
Multiply distance by 2 for 24 volt systems
Multiply distance by 4 for 48 volt systems

Example: For a 50W light bulb at 12V: I = P/U = 50W/12V = 4.2A. With #10 wire (5.26 mm²) at 2% voltage drop, maximum wire length is approximately 8m total (4m single direction).