Conductor Ampacity & Wire Sizing Calculator

Size conductors under NEC Article 310 — pick load, material, insulation, and terminal rating, then apply ambient temperature correction and bundling adjustment factors in the correct code order to land on a compliant AWG/kcmil size.

AVAILABLEAUTOMATED CHECKS ONLYSTANDARDS-AWAREINTERMEDIATENECWHAT DO THESE STATUSES MEAN?

NEC • 310.16110.14(C) TERMINAL CAPAMBIENT + BUNDLINGCOPPER / ALUMINUM

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Overview

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.

App preview

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

Inside the lab

Example data — not a real field report

Dashboard with rule-by-rule NEC checks — Dashboard — every mandatory NEC check (ampacity, 110.14(C) terminal cap, 240.4 protection, continuous load, ambient, bundling) returns pass/warn/fail with the section cited, and an overall CODE PASS badge lights only when all mandatory checks pass.

Ampacity charts and correction curves — Charts & Graphs — ampacity vs. AWG/kcmil curves with your operating point marked, plus ambient and bundling correction curves showing exactly how each factor bends the allowable ampacity.

Step-by-step calculation trace — Calculation Trace — the full derivation printed step by step, citing 310.16, 310.15(B)(1), 310.15(C)(1), 110.14(C), 215.2, and 240.4 so the result is defensible in a code review.

Detailed engineering results — Detailed Results — selected conductor, corrected ampacity, terminal-limited ampacity, applied correction and adjustment factors, chosen OCPD, and utilization percentages laid out as a printable calc sheet.

Design challenge mode — Design Challenge — randomized sizing problems (load, ambient, bundling, material) with your submitted AWG graded against the correct answer and a diff of factors applied.

Learn and quiz on ampacity sizing — Learn & Quiz — the correct-then-cap rule (correct on the 90°C column, then cap at terminal rating), continuous-load treatment, common mistakes, and copper-vs-aluminum trade-offs, followed by a short quiz.

Code references and table lookups — Code References — every NEC section and table used, with the exact ampacity, ambient, and bundling values pulled from your inputs so you can verify the lookup by hand.

What you'll do

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

What this lab is not

Not a design document, stamped calculation, or approval record.
Not a substitute for engineering analysis by a licensed professional.
Not a reproduction of NEC tables — values are computed and cited, and you must verify against the code edition enforced in your jurisdiction.
Not connected to live equipment and not a safety device.

Calculation basis

References NEC. Results are computed from the entered inputs and cited back to the referencing clause or table number — no code text or table is reproduced verbatim.

Simplifying assumptions are stated in the lab itself; where a model is intentionally conceptual, the lab says so rather than implying study-grade accuracy.

Standards basis: Standards-aware. Validation state: Automated checks only (last checked 2026-08-15).