Wire Size Calculator – DC Voltage Drop, AWG & mm² Cable Size
This free DC wire size calculator estimates the conductor area needed to meet your selected voltage-drop limit. Enter the length of one cable: either the positive (+) cable or the negative (−) cable. Do not add their lengths together. This calculator assumes both cables have the same length. Enter voltage and either current or power. Choose copper or aluminum. The result covers voltage drop only, not a complete cable or installation specification.
Need to work out your daily energy use first? Use the off-grid power calculator. The DC cable sizing guide explains the calculation. This tool estimates cable size from voltage drop; it does not check current-carrying capacity, fuse selection or installation conditions.
Example: Enter 5 m for one cable (whether positive or negative), not 10 m for both cables together; 12 V, 120 W, copper, and a 2% voltage-drop limit. Leave current empty. The calculator uses 10 A and returns 7.29 mm², with 10 mm² as the next listed size. The displayed 0.24 V is your selected limit (12 V × 2%), not the calculated drop through a 10 mm² cable. This example is not a cable or fuse approval.
How to Use This DC Wire Size Calculator
Enter the length of one cable (+ or −) (meters, cm, feet, or inches). Do not add both cables; the calculator assumes they have the same length.
Select your voltage-drop limit. The 2% default is a setting, not a universal requirement.
Enter voltage and either current or power. Leave the other field empty.
Read the calculated conductor area and next listed size. Check current-carrying capacity, protection and installation requirements separately.
Common DC Applications
Solar panel to charge controller
Caravan, camper or RV battery wiring
Marine DC systems
Off-grid power setups
Home battery system setups
FAQ – DC Wire Size Calculator
This calculator estimates conductor area for a selected voltage-drop limit in a DC circuit. It does not determine a complete cable specification or verify installation safety.
No. This tool is intended only for DC circuits. AC wiring follows different standards and is regulated
by national electrical codes. For household or industrial AC systems, always follow local code or
consult a licensed electrician.
Enter the length of just one cable: either the positive (+) cable or the negative (−) cable. Do not add their lengths together. This calculator assumes both cables have the same length. Enter voltage and either current or power, leaving the other field empty. Other cable and installation checks are separate.
There is no single limit for every circuit. Choose a limit appropriate to your equipment and applicable installation requirements. The 2% setting is the calculator default, not a universal requirement.
A longer cable increases voltage drop for the same conductor area and current. Enter the length of just one cable: either the positive (+) cable or the negative (−) cable. Do not add their lengths together. This calculator assumes both cables have the same length.
Voltage drop is the voltage lost along the conductors, reducing the voltage available at the load. This tool sizes conductor area against your selected limit; it does not check current-carrying capacity, fuses or installation conditions.
