Conductor Ampacity & Wire Sizing Calculator

Conductor ampacity sizing is the foundational NEC calculation behind every branch, feeder, and service — and it is where the most common code violations originate, because the correction and adjustment factors from Article 310 must be applied in a specific order and then re-checked against the terminal temperature limit of 110.14(C). This calculator walks the full sequence: enter load in amps or kVA, select single- or three-phase and voltage, then configure continuous-load percentage (125% multiplier), conductor material (copper or aluminum), 90°C insulation column starting point (THHN/THWN-2, XHHW-2), terminal temperature cap (60°C or 75°C per 110.14(C)), ambient temperature (with correction factors from Table 310.15(B)(1)), and bundling count (adjustment factors from Table 310.15(C)(1)). The Dashboard tab returns the minimum compliant AWG/kcmil, corrected ampacity, and utilization gauge with a rule-by-rule pass/fail check for every mandatory NEC citation. The Charts tab plots ampacity vs. size curves with the operating point marked, and shows how ambient and bundling factors bend the curve. The Calculation Trace tab prints a step-by-step derivation citing every section — 310.16, 310.15(B)(1), 310.15(C)(1), 110.14(C), 215.2, 240.4 — so the result is defensible in a design review. The Design Challenge tab generates randomized sizing problems with graded results. The Learn & Quiz tab covers the correct-then-cap rule (correct on the 90°C column, then cap at terminal rating), continuous-load treatment, copper-vs-aluminum trade-offs, and NEC edition changes. The Code References tab summarizes every applicable section with the exact table lookups used. Supports NEC 2017, 2020, and 2026 editions.

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A live look at the app you'll launch — every control on the left drives the visualizations on the right in real time.

• 01Look up conductor ampacity from NEC Table 310.16 on the 90°C column, then cap the result at the terminal temperature rating under 110.14(C)
• 02Apply the ambient temperature correction factor from Table 310.15(B)(1) for conductors installed above or below the 30°C base ambient
• 03Apply the bundling adjustment factor from Table 310.15(C)(1) when more than three current-carrying conductors share a raceway or cable
• 04Apply the 125% continuous-load multiplier to the minimum conductor ampacity and coordinate with the OCPD rating
• 05Compare copper vs. aluminum (or CCA) for a given load and explain the size, terminal, and cost trade-offs
• 06Trace an ampacity result end-to-end citing every NEC section used, and defend the selected AWG/kcmil in a design review