Extension Cord Voltage Drop Calculator
Long cords and heavy loads can cause voltage drop. Enter the one-way cord length from outlet to equipment, load amps, voltage, and AWG wire gauge to see whether the cord is a reasonable fit.
Last updated: May 2026
Buying and sizing notes
- For high-draw tools, use a shorter and heavier-gauge cord. Check tool and cord ratings before use.
How to use the cord result
Voltage drop is not only about whether the cord reaches. Long, light-gauge cords can make motors, compressors, pumps, and high-draw tools run hot or perform poorly.
Length is one-way
Enter the cord length from outlet to equipment. The calculator accounts for the electrical path out and back.
Amps matter
Use the amperage from the tool, appliance, charger, or nameplate. If you only know watts, divide watts by volts for a rough amp estimate.
Lower AWG is heavier
A 12 AWG cord is heavier than 14 AWG. Heavy loads and long distances usually need lower-number/heavier cords.
Motors need extra caution
Compressors, saws, pumps, and other motor loads can be more sensitive to voltage drop than simple lights or chargers.
How to use this estimate
What this includes
- One-way cord length
- Current draw in amps
- Voltage
- AWG wire gauge
- Round-trip conductor length
What it does not include
- Cord condition
- Temperature effects
- Code approval
- Motor startup behavior
- Manufacturer-specific tool limits
Common mistakes
- Using cord length as there-and-back distance
- Assuming a thin extension cord is fine for heavy loads
- Ignoring voltage drop on motors and compressors
- Using an unrated or damaged cord
Quick questions
Is extension cord length one-way or round-trip?
Enter the one-way cord length from the outlet to the tool or appliance. The calculator accounts for the round-trip conductor path internally.
What voltage drop is acceptable?
Lower is better. A 3% target is a common planning limit for many loads, while some temporary uses may tolerate more. Sensitive equipment, motors, and compressors should be treated more cautiously.
Is a lower AWG number heavier?
Yes. 12 AWG is heavier than 14 AWG, and 10 AWG is heavier than 12 AWG. Heavier cord generally has less voltage drop for the same length and load.
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