Power Cord Length Guide: How Long Should Your Cord Be? (Voltage Drop Explained)
“How long should my power cord be?” is one of the most common questions we get — and the correct answer is never just “make it longer.” Cord length interacts with gauge, current, and voltage to determine whether your equipment gets clean power or a degraded supply. This guide explains the real physics, gives you practical length rules by use case, and shows how length and gauge work together.
Why length is not just convenience
Power cord length affects two things: voltage drop and impedance. As current travels down a cord, the cord’s resistance converts a small amount of voltage into heat. The longer the cord and the thinner the gauge, the larger that loss. For most short indoor cords the loss is negligible. For long cords or high-current loads, it becomes a real constraint that can cause a device to draw more current, overheat the cord, or fail a certification inspection.
The practical rule: voltage drop is proportional to length and inversely proportional to gauge. Double the length and you double the drop. Step up one gauge (thicker wire) and you cut the drop.
Voltage drop: the numbers that matter
For a standard 120 V US cord set carrying 10 A:
| Length | 18 AWG drop | 16 AWG drop | 14 AWG drop |
|---|---|---|---|
| 2 m (6 ft) | ~0.7 V | ~0.5 V | ~0.3 V |
| 5 m (16 ft) | ~1.8 V | ~1.2 V | ~0.8 V |
| 10 m (33 ft) | ~3.6 V | ~2.4 V | ~1.5 V |
A drop under ~3% of line voltage is generally acceptable. That means a 10 m cord at 10 A should not stay at 18 AWG — move to 16 AWG or 14 AWG. The same principle scales with current: a 20 A load needs a thicker gauge than a 10 A load at the same length.
How long should your cord be? Rules by use case
- Desktop electronics (monitor, PC, printer): 1.5–2 m is standard. Longer than that is rare and usually a sign of a misplaced outlet, not a cord problem.
- General appliance / home: 3–5 m covers most rooms. Keep the gauge at 16 AWG or above for anything above 10 A.
- Workshop / power tool: 5 m, 14 AWG, rated for the tool’s current. Do not extend with a thin cord to save cost.
- Extension cord (outdoor, garden, construction): 10 m or more. Use a heavy-gauge SJOW/SJTW outdoor jacket and 14 AWG (or 12 AWG for 20 A). This is where voltage drop actually bites.
- Data center / rack: keep cords a consistent 2 m to the PDU. Do not compensate for a long run by adding a thin extension — reroute the PDU or step up the gauge.
Length and gauge must be sized together
The mistake we see most is buying a long cord at the wrong gauge. A 10 m extension cord at 18 AWG under a 15 A load will drop several volts and run warm. The fix is not “a longer cord” — it is the right gauge for the length. If you increase the run length, increase the gauge. If you increase the load, increase the gauge.
A simple sizing approach:
- Measure the longest safe, unobstructed run from outlet to device.
- Check the device’s current rating on the nameplate.
- Pick a gauge that keeps voltage drop under ~3% for that length and current.
- Choose the jacket for the environment (SVT/SJT indoor, SJOW/SJTW outdoor).
- Add a small margin for cable management — do not buy the cord at the absolute minimum.
When “just make it longer” is the wrong answer
If the honest answer is that the cord needs to be very long to reach the outlet, the better solution is usually to relocate the outlet or add a proper distribution point (a rated PDU or a grounded power strip), not to stretch a single thin cord across the room. An oversized cord run is a voltage-drop and fire-safety issue, and it will not pass a certification inspection at the destination market.
How HENG-WELL can help
HENG-WELL builds power cords from 18 AWG up to 10 AWG in lengths from standard 1.5 m desktop runs to long outdoor extension cords, with the gauge, jacket (SVT, SJT, SPT, SJOW, SJTW), and plug matched to the load and environment. For high-current or long-run applications — data centers, workshops, outdoor events — we size the gauge against the voltage drop so the cord arrives at the device doing exactly what the nameplate expects.
Send us the run length, the device current, and the environment, and we will recommend the correct gauge and jacket before you place the order.
HENG-WELL — power cords and connectors manufactured to global standards since 2011.
