Extension Cord Gauge Selector – Online Amps, Length & Voltage Drop

For 15 amps at 120V on a 50-foot cord, 14 AWG is typically sufficient (voltage drop ~3.1%). For longer runs of 100 feet or more, upgrade to 12 AWG to keep voltage drop under 5%. Always check the cord's label for its rated ampacity — 14 AWG is rated for 15A, 12 AWG for 20A.

Voltage drop is directly proportional to cord length. Doubling the length doubles the voltage drop. This is because electrical resistance increases linearly with distance. For long runs (100ft+), you need a thicker wire (lower AWG number) to compensate. For example, a 15A load on a 50ft 14AWG cord drops ~3.1V, but at 100ft it drops ~6.2V — exceeding the 5% recommendation for 120V systems.

14 AWG is thinner, lighter, and rated for up to 15 amps. 12 AWG is thicker, slightly heavier, and rated for up to 20 amps. The key difference: 12 AWG has about 37% less resistance than 14 AWG, meaning less voltage drop and less heat generation. For power tools, air conditioners, or any sustained high-draw device, 12 AWG is the safer choice — especially at distances over 50 feet.

Generally, no. 16 AWG extension cords are only rated for about 10-13 amps and are intended for light-duty use like lamps, phone chargers, or small electronics. Most power tools draw 12-15 amps and require at least 14 AWG. Using a 16 AWG cord with a circular saw or space heater can cause dangerous overheating. Always match the cord to the tool's amperage rating.

Voltage drop is the loss of electrical pressure as current flows through a wire's resistance. Excessive voltage drop causes: motors to run slower and hotter, lights to dim, and sensitive electronics to malfunction. The NEC recommends keeping voltage drop under 3% for branch circuits and 5% total (including the extension cord). For a 120V circuit, 5% = 6V of acceptable loss.

RVs typically use 30A (120V) or 50A (240V) service. For a 30A RV on a 50ft cord, 10 AWG is recommended (voltage drop ~3.5%). For a 50A RV, 6 AWG is needed. Never use a standard household 14 AWG or 12 AWG cord for RV hookups — the amperage demand far exceeds their capacity, creating a serious fire risk. Always use RV-specific cords with the proper NEMA plug configuration.

Yes. Outdoor extension cords have thicker, more durable insulation (often labeled "SJTW" or "SJTOW") that resists moisture, UV rays, and abrasion. Indoor cords use lighter insulation (like "SJT") and should never be used outside. For outdoor use, also look for cords rated for cold weather if you're in a freezing climate, as some insulation becomes brittle in low temperatures. The gauge selection rules remain the same regardless of indoor/outdoor.

AWG (American Wire Gauge) is a standardized system for measuring wire diameter. The key thing to remember: smaller AWG numbers = thicker wire. For example, 10 AWG is thicker than 14 AWG. Each 3-gauge decrease roughly doubles the cross-sectional area. The system is logarithmic — 10 AWG is about 2.6× thicker than 14 AWG. Common extension cord gauges are 16, 14, 12, and 10 AWG.