Pick a cord by matching its amp rating and wire gauge to your tool’s current draw, with heavier 12-gauge wire for big loads.
Buying an extension cord by length alone is the fastest way to burn out a tool or trip a breaker. The right cord for a hedge trimmer and a space heater are completely different, and getting the wire gauge wrong is the mistake that starts fires. Here’s the simple way to match any device to the cord it needs.
What Size Cord Do I Need? Start With The Amp Draw
Every appliance has a nameplate or manual that lists its current draw in amps. That number is your starting point. If you only see watts, divide watts by voltage — a 1,500-watt heater at 120 volts draws 12.5 amps.
When plugging multiple devices into a multi-outlet cord, add their amp draws together. The cord’s rating must meet or exceed that total.
Extension Cord Gauge Guide: What The Numbers Mean
Wire gauge, measured in AWG, is the single most important spec on a cord. Lower numbers mean thicker wire and higher current capacity. A 10-gauge cord carries far more than an 18-gauge cord.
- 18 AWG: Very light loads — lamps, phone chargers.
- 16 AWG: Light-duty tools and electronics on short runs.
- 14 AWG: Medium-duty appliances and tools.
- 12 AWG: Heavy-duty tools, heaters, and shop equipment.
- 10 AWG: The heaviest portable loads.
For a general-purpose home or garage cord, most guides point to a 15-amp, 12-gauge cord as the versatile choice — it handles almost any consumer tool you’ll plug into it.
Why Length And Environment Change Your Pick
Longer cords add resistance and voltage drop, which starves your tool of power. Keep runs as short as practical, and step up to a heavier gauge when the distance stretches out. A 16 AWG cord might be fine for a 25-foot run but undersized for the same load at 100 feet.
Environment matters just as much. Outdoor cords carry a “W” marking for weather resistance; “O” means an oil-resistant jacket. Never use an indoor-only cord outside or in damp spots, and run any cord that touches wet conditions through GFCI protection. Also look for UL or ETL certification, an independent lab’s sign the cord meets safety standards.
| Wire Gauge | Typical Use | Best For |
|---|---|---|
| 18 AWG | Very light loads | Lamps, phone chargers |
| 16 AWG | Light-duty, short runs | Small power tools, electronics |
| 14 AWG | Medium-duty | Lawn tools, shop vacs |
| 12 AWG | Heavy-duty | Circular saws, heaters, pressure washers |
| 10 AWG | Very heavy | Large stationary tools |
A few habits keep any cord safe. Inspect the cord before every use, and replace anything with frays, exposed wires, or damaged plugs. Avoid running cords under rugs or through pinch points and heat sources, which damage the insulation. Extension cords are temporary wiring — they are not meant to run through walls, ceilings, or concealed spaces, and they should never be daisy-chained or overloaded. Unplug cords when they’re not in use.
When your garden tools or outdoor gear need a reliable connection, our tested lineup of best cord extension options shows which models hold up season after season.
References & Sources
- Grainger KnowHow. “Choosing the Right Extension Cord.” Explains amp ratings, AWG, and load matching.
FAQs
Can I use a 16-gauge cord for my lawn mower?
Yes, if the cord run is short and the mower’s amp draw fits within 16 AWG’s rating. For longer runs or heavier mowers, step up to 14 or 12 gauge to avoid voltage drop.
What happens if I use a cord that’s too light?
The cord heats up because the wire can’t carry the current easily. That heat damages insulation, drops voltage to your tool, and creates a fire risk. A tool that runs sluggish or a warm cord are both signs you’ve undersized the wire gauge.
Is it safe to plug two cords together?
Daisy-chaining cords is not recommended. Joining two cords increases resistance and creates a weak point at the connection, which can overheat. If you need more reach, buy a single cord rated for the full distance and load rather than linking two shorter ones.