Cable Size Calculator: NEC 2023 AWG & mm² Screening

Cable size chart (amps → AWG / mm²)

Field-style cable size chart / electric / battery cable sizing chart from the same IEC 60228-style ladder used in the calculator (typical copper screening). Click a current to load the calculator; verify tabulated ampacity after derating and voltage drop. AWG is an approximate NEC cross-check only—not conduit trade size.

Conduit sizing for wire? This page sizes conductor ampacity, not raceway trade size. After you pick AWG/mm², use NEC Chapter 9 Annex C (or manufacturer fill tables) for conduit/EMT fill %. In conduit, still apply ambient + grouping derating (Advanced Ca/Cg) before locking the BOM.

Ambient & grouping derating — screening reference

Illustrative correction factors only—do not stamp these numbers into a final design. Enter Ca/Cg from the adopted edition tables (for U.S. projects typically NEC 2023 ambient/adjustment notes under Art. 310; elsewhere IEC 60364-5-52, BS 7671 Appendix 4, etc.). This calculator’s mm² ladder is underrated from design current; Advanced Ca/Cg only inflate the screening current.

Example ambient correction (illustration only — not a code reprint)

Example bundling / grouping adjustment (NEC-style illustration)

Combined derating example: Design current 63 A → screening ladder suggests 16 mm² Cu. If ambient 41–45 °C (factor 0.88) and 4–6 grouped conductors (factor 0.80), required tabulated ampacity ≥ 63 ÷ (0.88 × 0.80) ≈ 89 A → upsize to the next ladder step (often 25 mm² for Cu screening). Then check voltage drop and OCPD coordination.

OCPD type (fuse vs breaker): see Fuse vs Breaker Sizing Guide.

Cable sizing method & formula context

I

Design load current in amperes (RMS, steady-state basis you are sizing for).

V

Nominal system voltage in volts (line-to-neutral for single-phase, line-to-line for three-phase).

mm²

Conductor cross-sectional area per IEC 60228 standard sizes; output here is always an integer mm² step.

Ampacity

Tabulated allowable current for a conductor under stated conditions; must be derated for grouping, ambient, and installation method.

PF (cos φ)

Power factor when converting from kW to kVA before finding line current.

Obtain design current: single-phase I = kVA × 1000 ÷ V; balanced three-phase I = kVA × 1000 ÷ (√3 × V) with √3 ≈ 1.732. From kW: kVA = kW ÷ PF, then use the line-current formula for your phase.

Screening rule (this tool): pick the smallest standard mm² whose ladder step current is ≥ I (or ≥ It when Advanced Ca/Cg are set, with It = Ib ÷ (Ca × Cg)). This is not a substitute for manufacturer ampacity tables, harmonics, insulation temperature rating (for example XLPE 90 °C), or short-circuit/adiabatic withstand proofs.

Solar / PV DC strings (solar panel cable size calculator path): Click the PV DC string · 27.5 A preset (Isc 11 A × 2 parallel × 1.25 → often ~6 mm² / ~10 AWG before derating), or enter your own Isc × N_parallel × continuous-current factor from the series-parallel calculator. Method: how to size solar DC cable. Confirm with MPPT sizing and the Solar calculators hub—this page absorbs solar DC cable screening; not a separate PV-cable-only tool.

Worked example: Module Isc 11 A, 2 parallel → 11 × 2 × 1.25 = 27.5 A design. Enter 27.5 A (DC 2-wire) on this calculator—screening often lands near ~6 mm² / ~10 AWG before derating and voltage-drop upsizing. Then check one-way length under Advanced / voltage drop.

12 V / 24 V / 48 V battery & inverter DC: Enter continuous DC amps (or use Quick presets), set Phase to DC (2-wire) and voltage to 12/24/48. Ampacity screen gives AWG + mm²; then set one-way length (ft) under Advanced and open NEC voltage drop—low-voltage DC % loss climbs fast on long runs.

VFD / motor feeder screening: Use motor FLA × code factor (often 125%) as design amps, or the VFD preset (~63 A). This screens ampacity only—drive cable length, PWM reflections, and shield rules need manufacturer guidance after the ampacity + voltage-drop check.

Worked example (with numbers)

Given: 37 kW production load, PF 0.85, 400 V three-phase copper feeder.
Step 1 — kVA: 37 ÷ 0.85 ≈ 43.5 kVA.
Step 2 — line current: 43.5 × 1000 ÷ (1.732 × 400) ≈ 62.8 A → use 63 A design current.
Step 3 — screening mm²: 63 A maps to the next ladder step → 16 mm² Cu (integer output).
Step 4 — verify: apply grouping/ambient derating on project tables; check route length with the voltage drop calculator; confirm OCPD and fault current withstand with the breaker size calculator.

480 V three-phase · 100 A (SERP-style): Enter 100 A, 480 V, 3φ, Cu (or use the 480 V 3φ · 100 A preset). Screening often lands near 35 mm² / ~2 AWG before derating—then apply Ca/Cg and check NEC voltage drop for a 150 ft one-way run. This is a planning screen, not a full NEC Table 310.16 fill for every install method.

Common Cable Sizing Scenarios

Illustrative screening rows only—not a stamped bill of materials. AWG values below are read against NEC 2023 Table 310.16 copper columns under the stated temperature basis, ≤3 current-carrying conductors, and 30°C ambient before installation corrections. They do not auto-apply small-conductor OCPD limits (e.g. 240.4(D)-style), parallel-set rules, or terminal exceptions. Confirm on the locally adopted edition.

Voltage Drop Calculation Example

When cable runs are long, voltage drop often governs the size—not ampacity. Informational notes in many NEC editions mention about 3% on a branch and 5% feeder + branch total as planning targets—not automatic pass/fail ampacity rules. Use the resistive formula for a quick screen:

Vd = 2 × L × I × R ÷ 1000 (single-phase) or Vd = √3 × L × I × R ÷ 1000 (3-phase), where L = one-way length in feet, I = current in amps, R = conductor resistance in Ω/1000ft.

For 3-phase loads, replace the factor of 2 with √3 (1.732). For aluminum conductors, use ~1.6x the resistance of copper at the same AWG. Always confirm with manufacturer voltage drop tables for final design.

Installation method (why OEM tables still win)

Ampacity changes with how the cable is installed. Use Advanced Ca/Cg for a quick upsize; confirm final size on project IEC/NEC tables (Southwire/Eland-class tools encode these factors in brand software—we stay method-agnostic for planning).

Use the suggested mm² as an early BOM or panel schedule checkpoint, then validate against detailed manufacturer tables including ambient, installation method, and voltage drop along the route.

Next step after screening: combine your candidate size with breaker frames and source ratings using the breaker size calculator, transformer size calculator, and generator size calculator, then confirm against IEC/NEC tables. Browse the protection calculators hub for the full lane.

Common standards designers cross-check

Cable sizing in practice is read against the locally adopted wiring rules and tabulated ampacity—for U.S. projects this page’s AWG screen is bound to NEC 2023 Table 310.16 (older editions used 310.15(B)(16)); elsewhere use IEC 60364, BS 7671, AS/NZS 3008, or manufacturer tables. The mm² output is an IEC 60228-style ladder for early screening, not a full IEC ampacity selection for installation method.

NEC / AWG cross-check for US projects

After you have a candidate mm², map to approximate AWG/kcmil and confirm allowable amps under the adopted NEC edition (temperature rating, ambient, bundling, small-conductor/OCPD limits, and whether parallel conductors apply). The AWG screen on this page uses NEC 2023 Table 310.16 columns selected in Advanced; it still does not size parallel sets.

Quick PAA — what size wire for 100 amp service? At 240 V 1φ, many NEC 75°C Cu screens land near 3 AWG (use the 100 A panel · 240 V preset). At 480 V 3φ, screening often lands near 3 AWG Cu / 1 AWG Al (75°C) or ~35 mm² on the IEC ladder—always apply ambient/bundling and match OCPD with the breaker size calculator.

3-phase motor cable sizing (FLA screen)

Motors: take nameplate or NEC Table 430.250 FLA, apply continuous/branch factors from your code (often 125% of FLA for conductors), enter that design amps above for mm² screening, then map to AWG. Example: ~50 HP @ 460 V ≈ 65 A FLA → 65 × 1.25 ≈ 81 A → screening ladder often ~25 mm² / 4 AWG Cu before voltage drop and starting voltage dip—see motor starting & protection.

Last updated: 2026-09-13. mm² screening + AWG illustration only—not a reprint of NEC Table 310.16 or IEC 60364-5-52.

References

• NFPA 70 (NEC) — ampacity & wiring methods
• IEC TC 64 / IEC 60364 wiring overview
• Engineering Toolbox — AWG wire gauges

Installation method, grouping & fault current

Real ampacity depends on how the run is installed—for example in conduit, on cable tray, buried, or in free air—together with grouping/bundling and ambient temperature derating. Use Advanced Ca/Cg for a quick upsized screen; still confirm final ampacity on your IEC/NEC project tables.

Fault current & protection: available fault current, device let-through, and adiabatic thermal limits can require a larger conductor than steady-state ampacity. Size OCPD and check short-circuit withstand after screening—see the breaker size calculator and motor starting & protection guide for coordination context.

More context: Voltage drop calculation · kW to kVA Formula Explained · 3-Phase Power Calculator · When to Use kVA Instead of kW

3-phase cable size chart (kW → A → mm² / AWG)

Screening look-up at PF 0.85 copper, underrated (Ca = Cg = 1). Line current Ib = P ÷ (√3 × V × PF). AWG is an approximate NEC cross-check only. Enter the same kW in the calculator (From kW) or apply Advanced derating when ambient/grouping apply.

After screening, check long feeders on the voltage drop calculator and OCPD on the breaker size calculator.

Frequently Asked Questions