Calculate proper wire sizes per NEC 2023. Includes ampacity, voltage drop, ambient temperature, conduit fill, terminal rating, and continuous load checks.
To determine the correct conductor size, start by selecting your material (Copper or Aluminum), system voltage, and phase configuration. Enter the connected load in Amps and specify if it is a continuous load; if checked, the tool automatically applies the NEC-mandated 125% multiplier for circuit sizing.
Next, account for environmental factors by entering the one-way run length and the ambient temperature. If your installation includes more than three current-carrying conductors in a single raceway, adjust the conduit fill count. The tool will then reference NEC Table 310.15(B)(1) and (2) to apply the necessary derating factors to the base ampacity.
Finally, set your terminal temperature rating (typically 60°C for circuits under 100A or 75°C for larger equipment) and your desired voltage drop limit (standard 3%). Click "Calculate" to receive an NEC-compliant wire size recommendation that accounts for ampacity, terminal limitations, and voltage drop simultaneously.
In electrical engineering and contracting, "sizing by the breaker" is a dangerous oversimplification. We built this NEC Wire Sizing Calculator to handle the multi-step verification process required by the 2023 National Electrical Code (NEC). Sizing a conductor correctly isn't just about the load; it’s about accounting for the physics of the installation environment—including heat, distance, and the number of wires in a single raceway.
What sets this tool apart is its comprehensive compliance engine. It doesn't just pull from NEC Table 310.16; it applies the mandatory adjustments for ambient temperature and conduit fill (adjustment factors). It also enforces the 125% rule for continuous loads (per NEC 210.19) and respects the "Weakest Link" principle by checking terminal temperature ratings ($60^{circ}C$ vs $75^{circ}C$), ensuring your wire choice doesn't exceed the rating of the equipment it connects to.
Beyond safety, the tool addresses performance through voltage drop calculations. While the NEC technically lists voltage drop as a recommendation rather than a hard requirement, professional standards dictate a 3% limit for branch circuits to prevent equipment damage and energy waste. This calculator allows you to balance copper or aluminum costs against electrical performance, giving you a defensible, code-compliant specification for any project.
Code Professional Tip: Remember the "Small Conductor Rule" (NEC 240.4(D)). Even if the ampacity tables say a #12 AWG copper wire can carry more, it is generally limited to a 20A overcurrent protection device. Always use this tool as a primary check, but verify your final selection against the specific Overcurrent Protective Device (OCPD) being used in your panel.
Yes. It uses NEC 2023 tables for ampacity, derating, voltage drop, and terminal ratings.
Per NEC 210.19 and 215.2, continuous loads require wire ampacity ≥ 125% of the load.
3% by default for branch circuits (5% total system), adjustable by user.
Yes. Select your conductor material in the input form.
Yes. NEC Table 310.15(B)(1) and (2) adjustments are applied.
Yes. You can customize voltage drop target or disable the check.