Electrical Tools

NEC-based sizing calculators for electricians and installers. All free, no signup required.

Voltage Drop Calculator

Calculate voltage drop by gauge, current & distance against the NEC 3%/5%

Electrical Load Calculator

Estimate a home's service load and panel size with the NEC standard method

Wire Size Calculator

Find the minimum copper wire gauge for a load using NEC ampacity

About these electrical calculators

Electrical sizing has little room for error — undersize a conductor or overload a service and you create a code violation or a fire risk. These free calculators apply standard NEC methods so electricians and installers can size wire, check voltage drop, and estimate service load on the spot.

The Wire Size and Voltage Drop calculators help you pick the right copper conductor for a load and distance against the NEC's 3%/5% recommendations, and the Electrical Load calculator estimates a home's service and panel size using the NEC standard method. Treat them as fast field references — the authority having jurisdiction and the adopted code edition always govern the final design.

Frequently Asked Questions

Which NEC edition do these follow?
They use long-standing standard methods — ampacity tables, the 3%/5% voltage-drop guideline, and the standard load-calculation method. Always verify against the NEC edition adopted in your jurisdiction, since local amendments apply.
Is voltage drop a code requirement?
In most cases the NEC 3%/5% figures are recommendations rather than hard limits, but many jurisdictions and project specs enforce them. The calculator flags where you exceed them so you can upsize the conductor.
Do these size conduit or account for derating?
They cover conductor ampacity, voltage drop, and service load. For conduit fill, ambient and bundling derating, and final design, use the full NEC tables or design software.
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