Voltage drop--
Voltage drop--
Extension Cord Voltage Drop Calculator
Estimate voltage drop for an extension cord from amps, length, voltage, and wire gauge.
How to use this calculator
Enter the measurements or usage numbers you know, then use the result as a planning estimate. The defaults are realistic starting points, but the best result comes from replacing them with your actual product, property, trip, or equipment numbers.
Practical planning tips
- Add a reserve for waste, weather, terrain, load, or product variation.
- Check labels, local codes, manufacturer charts, and safety requirements before buying materials or operating equipment.
- Round up when a shortage would stop the job, trip, or chore.
FAQ
Extension Cord Voltage Drop Calculator questions
Can I use this result for buying materials?
Use it as a planning estimate, then verify against product coverage, local requirements, and the conditions on your property or trip.
Why should I add a reserve?
Real projects and outdoor conditions rarely match the perfect math. A small reserve helps cover waste, uneven ground, spills, weather, and user input error.
How to use this estimate
The extension cord voltage drop calculator estimates how much voltage is lost through a cord based on amps, length, wire gauge, and supply voltage. It helps screen long cord runs for tools, generators, pumps, chargers, and temporary work setups.
Inputs that matter most
- Cord length from source to equipment, including the full one-way run used by the calculator.
- Load amps from the tool, appliance, charger, or equipment nameplate.
- Wire gauge and material from the cord label.
- Supply voltage and whether the cord is rated for the environment and load.
Formula and method
Voltage drop is based on current, conductor resistance, and length. The calculator estimates lost volts and percent drop so you can compare the setup with common planning limits and equipment requirements.
A low drop supports better equipment performance, but voltage drop is only one safety check. Cord amp rating, jacket type, grounding, GFCI protection, wet-location rating, and equipment instructions still matter.
Worked example
Example: a 12 amp tool on a 100 foot, 14 gauge cord may show a larger voltage drop than the same tool on a shorter 12 gauge cord. If the percent drop is high, the tool may run hot, start poorly, or trip protection. A shorter cord, heavier gauge cord, lower load, or different power source may be needed.
Common planning mistakes
- Using a light-duty indoor cord for outdoor, generator, or job-site loads.
- Adding multiple cords without recalculating total length and rating.
- Ignoring startup current from motors, pumps, compressors, and saws.
- Assuming a warm or coiled cord can safely carry the same load as a fully uncoiled cord.
Safety and disclaimer note
Extension-cord and voltage-drop estimates are not professional electrical advice. Follow cord labels, manufacturer specs, OSHA or job-site rules where applicable, GFCI requirements, local electrical code, and consult a qualified electrician for temporary power, generator connections, or permanent wiring.
FAQ
Practical questions
What percent voltage drop is acceptable?
Many planning references aim for a low percentage, but equipment manuals and electrical guidance should control final decisions.
Does a longer cord always drop more voltage?
Yes, for the same load and wire gauge, increasing length increases resistance and voltage drop.
Can a heavier gauge cord help?
Yes. A lower gauge number usually means a thicker conductor and less voltage drop for the same length and load.
Should I use this for permanent wiring?
No. Permanent wiring must follow electrical code and should be designed or reviewed by a qualified professional.
Why does a coiled cord matter?
A loaded coiled cord can retain heat. Follow the cord label and manufacturer instructions for safe use.
Cord rating checks
Before using a long cord, check the printed cord label for gauge, amp rating, grounding, outdoor rating, and temperature limits. The calculator can estimate voltage drop, but it cannot confirm that a damaged cord, undersized outlet, wet-location setup, or overloaded power strip is safe. If the equipment has a motor, test the setup under supervision and stop if the cord, plug, or tool becomes warm, smells hot, or trips protection.
For generator use, keep the generator outside and away from doors, windows, vents, garages, and crawlspaces because carbon monoxide can be deadly. Use cords and connections that match the generator manual, and get qualified electrical guidance for anything tied into building wiring.