Extension Cord Amp Rating & Safety Check
Check if your extension cord is rated for the load.
Enter AWG gauge, cord length, and device wattage to verify amp capacity and calculate voltage drop.
Extension cords are the most misused electrical product in the home. Using an undersized cord for a heavy load creates resistive heating inside the cord jacket, which is a fire risk — especially for cords rolled up in a coil, where heat cannot dissipate.
Gauge and amp ratings
Extension cord wire gauge follows AWG (American Wire Gauge) — lower numbers are thicker wires with lower resistance and higher amp capacity. The ratings below are for typical 120V extension cords at the lengths shown:
AWG 18: up to 10 A (suitable for lamps, phone chargers, small electronics — not power tools) AWG 16: up to 13 A (suitable for most household electronics, small power tools) AWG 14: up to 15 A (suitable for power tools, larger appliances up to 25-50 ft) AWG 12: up to 20 A (suitable for high-draw tools and appliances up to 100 ft) AWG 10: up to 25 A (heavy-duty industrial use)
Longer cords have higher total resistance. NEC guidelines recommend derating one AWG size for cords longer than 50 feet when carrying heavy loads.
Voltage drop
Voltage drop = current x 2 x length (ft) x resistance_per_foot
Resistance per 1,000 ft of copper: AWG 18 = 6.39 ohms, AWG 16 = 4.02, AWG 14 = 2.53, AWG 12 = 1.59, AWG 10 = 1.00.
The factor of 2 accounts for both the hot and neutral conductors (current flows out and back). NEC recommends keeping voltage drop under 3% for branch circuits; 5% is the practical upper limit before motors strain and lights dim noticeably.
Most common mistake
Using a light-gauge (AWG 16 or 18) cord for a space heater, shop vacuum, or air compressor. These draw 10-15 A continuously and will overheat an AWG 18 cord in minutes.