Wire Gauge Calculator — AWG Size for Any Current & Length
Find the correct cable AWG for any current, length, and voltage drop limit.
Free sizing tool
Solar Wire Gauge Calculator
Size your cables correctly — enter current, length, and voltage to get the right wire gauge with voltage drop and power loss calculated.
Cable parameters
Acceptable voltage drop
AWG to mm² reference
| AWG | mm² | Max amps (Cu, 60°C) | Common use |
|---|---|---|---|
| 14 | 2.08 | 15 A | Lighting circuits |
| 12 | 3.31 | 20 A | General outlets |
| 10 | 5.26 | 30 A | Small solar, dryer |
| 8 | 8.37 | 40 A | Solar string, range |
| 6 | 13.30 | 55 A | Sub-panel feed |
| 4 | 21.15 | 70 A | Battery bank |
| 2 | 33.63 | 95 A | Large battery bank |
| 1/0 | 53.49 | 125 A | Main service |
| 2/0 | 67.43 | 145 A | Inverter feed |
| 4/0 | 107.22 | 195 A | Heavy inverter feed |
Based on NEC ampacity tables for copper at 60°C. Always verify with local electrical codes and a licensed electrician.
AWG Wire Sizes: What the Numbers Mean
AWG (American Wire Gauge) uses a counterintuitive numbering system: lower numbers mean thicker wire. 14 AWG is thin household wire. 4 AWG is a thick cable you can barely bend by hand. 4/0 AWG (pronounced “four-ought”) is nearly as thick as your thumb. Each step down in gauge number increases the wire’s cross-sectional area by roughly 26% and its current-carrying capacity by roughly 20%.
| AWG | Diameter (mm) | Area (mm²) | Max Amps (30°C) | Common Use |
|---|---|---|---|---|
| 14 | 1.63 | 2.08 | 15A | Light switches, outlets (15A circuits) |
| 12 | 2.05 | 3.31 | 20A | Kitchen outlets, small solar arrays |
| 10 | 2.59 | 5.26 | 30A | Dryers, solar panel runs, water heaters |
| 8 | 3.26 | 8.37 | 40A | AC circuits, controller-to-battery |
| 6 | 4.11 | 13.3 | 55A | Battery-to-inverter (small systems) |
| 4 | 5.19 | 21.2 | 70A | Battery-to-inverter (12V systems) |
| 2 | 6.54 | 33.6 | 95A | Large inverters, sub-panels |
| 1/0 | 8.25 | 53.5 | 125A | Service entrances, large battery banks |
| 4/0 | 11.68 | 107.2 | 195A | Main service, 12V high-power systems |
Temperature Derating: Why Hot Environments Need Thicker Wire
The ampacity ratings above assume 30°C (86°F) ambient temperature. In hotter environments, wire insulation softens and the safe current-carrying capacity decreases. NEC requires derating: at 40°C, multiply ampacity by 0.91. At 50°C, multiply by 0.82. At 60°C, multiply by 0.71. Solar installations are particularly affected because conduit on a sun-exposed roof can reach 60-70°C in summer. A 10 AWG wire rated for 30A at 30°C can safely carry only about 21A at 60°C. Use the calculator above with your expected ambient temperature for accurate results.
Copper vs Aluminum Wire
Copper is the standard for solar installations because it has 61% higher conductivity than aluminum, allowing thinner cables for the same current. Aluminum is cheaper per pound but must be upsized by 1-2 gauges to match copper’s capacity (e.g., 2 AWG aluminum replaces 4 AWG copper). Aluminum also requires special terminations (anti-oxidant compound, compatible lugs) because it oxidizes faster than copper. For short runs (under 3 meters) and residential systems, copper is always the right choice. For long runs in commercial installations (30+ meters), aluminum can save significant cost if properly terminated.
NEC Code Requirements for Solar Wiring
The National Electrical Code (NEC) has specific requirements for solar PV wiring. Article 690 covers photovoltaic systems. Key requirements: (1) PV source circuit conductors must be rated for 125% of the short-circuit current (Isc), not the operating current. (2) All conductors exposed to sunlight must be rated for wet locations and UV exposure (USE-2, PV Wire, or XHHW-2). (3) Equipment grounding conductors must be sized per NEC Table 250.122. (4) Rapid shutdown requirements (NEC 690.12) may dictate additional wiring for module-level shutdown. Always verify your wire sizing meets local code requirements — the calculator provides the engineering minimum, but your jurisdiction may have additional rules.
For a full guide covering all three cable runs in a solar system, see our Solar Cable Sizing Guide.
Frequently Asked Questions
What AWG wire do I need for a 30 amp solar panel?
For a 30A solar panel run, the wire gauge depends on the cable length and acceptable voltage drop. At 3 meters with a 3 percent voltage drop limit on a 12V system, you need 10 AWG minimum. At 6 meters, you need 8 AWG. At 10 meters, you need 6 AWG. Enter your exact current, length, and voltage above for a precise recommendation.
What size cable do I need from solar panel to charge controller?
Use the panel’s maximum power current (Imp) as the amperage, the actual cable run length in meters, the panel string voltage (Vmp), and a 3 percent maximum voltage drop. For typical residential systems: 10 AWG handles up to 30A at 3 meters, 8 AWG handles up to 40A at 5 meters. The calculator above gives the exact gauge for your specific configuration.
What gauge wire for a 100 amp battery to inverter connection?
At 100 amps on a 12V system with a 1-meter run and 2 percent voltage drop limit, you need 2 AWG (33.6 mm²) minimum. At 1.5 meters, 1/0 AWG. At 2 meters, 2/0 AWG. This is the thickest and most expensive cable run in a 12V system — upgrading to 24V or 48V halves or quarters the current and dramatically reduces cable cost. See our voltage comparison guide for details.
Why is my solar panel voltage low at the charge controller?
The most common cause is voltage drop from undersized cables. If your panel produces 18V but the controller sees only 16V, you are losing 2V (11 percent) in the cable — which means the cable is too thin for the current and distance. Use the calculator above to verify your cable gauge is correct for the run. Other causes include partial shading, dirty panels, or a damaged MC4 connector with high resistance.
What happens if I use wire that is too thin for solar?
Three things happen: (1) energy is wasted as heat in the cable — typically 5 to 15 percent of your solar production; (2) the cable and connectors overheat, which can melt insulation and create a fire hazard; (3) voltage drop at the battery end prevents proper charging, which shortens battery life. Always size cables using this calculator and never go below the recommended AWG.
My battery is not reaching full charge — could it be the cable?
Yes, this is a common and overlooked problem. If the cable from the charge controller to the battery has excessive voltage drop, the controller thinks the battery is at a higher voltage than it actually is. For example, the controller reads 14.4V at its terminals (absorption voltage reached) but the battery only sees 14.0V due to 0.4V of cable drop — so it never reaches true full charge. Use 1 percent maximum voltage drop for the controller-to-battery cable run.