Undersized DC wire heats up and sags voltage at the inverter or controller. This DC cable size calculator takes current, one-way length, and bus voltage to suggest a conservative AWG with an estimated drop percentage for planning.
Benefits
- Picks AWG from ampacity tables for your load current.
- Checks ~3% voltage drop over the run length.
- Works for 12 V, 24 V, and 48 V battery buses.
How it works
- Enter steady or peak DC load current in amps.
- Add one-way cable length in feet and system voltage.
- Read recommended AWG and approximate voltage drop %.
FAQ
How does a DC cable size calculator work?
It selects the smallest standard AWG that carries your amps per conservative ampacity tables, then estimates voltage drop over round-trip resistance (out and back). Example: 40 A, 20 ft one-way, 12 V often lands near 4–6 AWG depending on drop target—verify with the tool for your exact inputs.
One-way or round-trip length?
Enter one-way distance from battery to load. Drop math doubles the length internally for positive and negative conductors. Measuring only half the loop understates resistance and oversizes wire optimistically.
When should I go one AWG size larger?
Inverter surge, lithium charge spikes, or long runs near 3% drop often warrant the next size up. Aluminum conductors need larger gauge than copper. Follow local electrical code for final installs—this calculator is for planning estimates.
Technical specifications
- Input: load_A, one-way_length_ft, system_V.
- Output: recommended AWG + ~% voltage drop.
- Drop uses round-trip copper resistance.
- Related: dc-cable-size, dc-cable-voltage-drop, watts-to-amps.
Amps and length drive gauge—not voltage alone
A DC cable size calculator needs load current and how far electrons travel. Higher amps need thicker copper; longer runs add resistance even at modest current. System voltage sets how many volts you can afford to lose—3% on 12 V is tighter than 3% on 48 V for the same absolute drop.
Ampacity first, voltage drop second
The tool picks a gauge that can carry the current without overheating, then reports approximate drop over your one-way length. If drop is high, step up one AWG even when ampacity barely passes—inverters and motors see sag as brownouts or nuisance trips at the DC bus.
Battery bank to inverter is the critical run
Size the heaviest DC segment: bank to inverter, controller to array, or winch feed. Convert load watts to amps with Watts to Amps when only nameplate watts are known. For manual drop on a chosen gauge, pair with DC Cable Size & Voltage Drop when you already picked a spool from stock.