Wire Gauge Calculator (AWG)

Find the minimum AWG/kcmil or IEC mm² wire size for a circuit, check the voltage drop and ampacity of a size you already have in mind, or combine multiple parallel conductors into an equivalent single size. Supports copper and aluminum, DC, single-phase, and three-phase AC, selectable 60/75/90°C conductor temperature, a continuous-duty 125% load factor, and NEC Table 310.16 ampacity alongside the NEC 3%/5% voltage-drop recommendation. Results include a bidirectional AWG↔mm² equivalent, an ampacity-headroom meter, and a wire-size comparison chart. Built for electricians, electrical engineers, solar and EV installers, and students.

Pick a calculation mode, set the circuit parameters, and click Calculate. A wire must clear both the NEC ampacity check and the voltage-drop limit to pass.

Standard

Phase

Conductor Temp

Conduit Type

Load Type

Quick Presets

Conductor Material

Wire Size (AWG / kcmil)

Number of Conductors (to combine, same size each)

Supply Voltage (select or enter custom)

Load (value + unit — total combined current for Combine mode)

Power Factor (AC — used for kW / hp conversion)

One-Way Circuit Length

Max. Allowable Voltage Drop (% — NEC recommends 3% branch)

Parallel Conductor Sets (1 = standard single run)

⚠️ Motor-load calculation (horsepower input): motor starting current, efficiency, service factor, and NEC Article 430 requirements are not modeled by this estimate. Use the Motor Starting Current Estimator and have a licensed electrician verify conductor sizing for any motor circuit.

⚠️ NEC 310.10(H) permits paralleling conductors 1/0 AWG (or 50 mm² in IEC) and larger only, with all sets identical in length, material, size, insulation, and terminations. The size selected here is smaller than that — verify with a licensed electrician before paralleling.

Results

Recommended Size

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Percent Drop

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Ampacity Rating

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Load Current

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Ampacity Used—

Formula: —

Wire-Size Comparison

Each bar is the percent drop for a neighboring conductor on the circuit you entered, shown beside the ampacity result. The size this page selected is marked in gold. The dashed line is the 3 percent branch-circuit mark. Use it to see whether a larger conductor is needed for the length of the run, not only for ampacity.

Neighboring Sizes Your Size 3% NEC Recommendation

🔌 Need to size the breaker or fuse for this circuit? Wire ampacity is only half the picture — use the Circuit Breaker Sizing Calculator to select the correct standard OCPD rating for this conductor.

🌀 Sizing wire for a motor circuit? Motor starting current, NEC Article 430 multiplying factors, and service factor aren't modeled here — use the Motor Starting Current Estimator for motor-specific conductor sizing.

Results are engineering estimates based on published NEC Table 310.16 general ampacity (30°C ambient, ≤3 current-carrying conductors) and conductor resistance and reactance at the selected operating temperature and conduit type. Actual ampacity and voltage drop vary with installation conditions. Verify with a licensed electrician before any electrical work.

How to Use the Wire Gauge Calculator

Choose the Calculation Mode

Pick Find Wire Size to get a recommended conductor for a new circuit, Check This Wire to evaluate a size you already have in mind, or Combine Conductors to find the ampacity and equivalent single size of multiple parallel conductors.

Set the Circuit Parameters

Select the wiring standard (NEC AWG/kcmil or IEC mm²), the phase, the conductor material, the 60/75/90°C temperature rating, and whether the load is Continuous Duty.

Enter the Load and Run Details

Enter the supply voltage, the load in amps, kW, kVA, or horsepower, and the one-way circuit length. Or tap a Quick Preset to fill a common scenario instantly.

Calculate, Review, and Print

Click Calculate to see the recommended size, ampacity headroom, voltage drop, and NEC verdict. Use Print to capture results and the chart exactly as they appear on screen.

Comprehensive Guide to Wire Sizing

Two independent checks, both must pass

Choosing a wire size means clearing two unrelated limits: ampacity (can the conductor carry the current without overheating, per NEC Table 310.16) and voltage drop (does the run's length cause too much voltage loss for equipment to work properly, per NEC 210.19/215.2). A wire can pass one check and fail the other — long, lightly loaded runs are usually voltage-drop-limited, while short, heavily loaded runs are usually ampacity-limited. This calculator checks both and recommends the smaller conductor that satisfies whichever constraint is tighter.

Continuous vs. standard loads

NEC 210.19(A)(1) defines a continuous load as one expected to run at maximum current for three hours or more — think EV chargers, water heaters, or commercial lighting left on for a full shift. Continuous loads must be sized at 125% of their current for ampacity purposes, which effectively pushes many circuits up one wire size compared to an intermittent load of the same nameplate current.

Combining parallel conductors

Running multiple smaller conductors in parallel instead of one large conductor is permitted by NEC 310.10(H) for 1/0 AWG and larger, provided every parallel set matches in length, material, size, insulation, and terminations. Combined ampacity is the sum of each conductor's individual rating, and the combined cross-sectional area corresponds to an equivalent single conductor size — useful for comparing a paralleled feeder against a single large conductor on cost, weight, or conduit-fill grounds.

AWG and mm² are the same idea, different units

Both systems describe a conductor's cross-sectional area — AWG numerically (lower number, thicker wire) and mm² directly. Switching the Standard toggle here converts your current selection to its closest cross-sectional-area match in the other system, the same conversion published in wire manufacturer datasheets.

Worked Examples

Three wire-size jobs, worked from a load and the limits on ampacity and drop. Load an example to run that job in the calculator above.

1. Continuous EV Charger Circuit — 240 V, 32 A, 35 ft

A 240 V single-phase EV charger draws 32 A continuously. With the 125% continuous-duty factor, the required ampacity is 40 A — 8 AWG copper meets that at 75°C. Does the 35 ft run also clear the 3% voltage-drop limit?

Required ampacity = 32 A × 1.25 = 40 A → 8 AWG (50 A @ 75°C). VD = 2 × 32 A × 35 ft × 0.778 Ω/kft ÷ 1000 ≈ 1.7 V → ≈ 0.7% — passes both checks.

2. Checking an Existing 12 AWG Circuit — 120 V, 16 A, 60 ft

An existing 120 V branch circuit uses 12 AWG copper at 75°C, carrying 16 A over a 60 ft run. Is the wire adequately rated, and what's the voltage drop?

Ampacity: 12 AWG = 25 A @ 75°C, well above 16 A (64% used). VD = 2 × 16 A × 60 ft × 1.98 Ω/kft ÷ 1000 ≈ 3.8 V → ≈ 3.2% — slightly over the 3% branch recommendation.

3. Combining Three 2/0 AWG Conductors — 480 V, 3Ø, 350 A

A 480 V three-phase feeder needs to carry 350 A. Three parallel 2/0 AWG copper conductors per phase are proposed. Is the combined ampacity sufficient, and what single conductor size is it equivalent to?

Combined ampacity = 3 × 175 A (75°C) = 525 A, well above 350 A. Combined area ≈ 3 × 67.4 mm² = 202 mm² ≈ equivalent to a single 400 kcmil conductor.

Quick Reference Table

NEC Table 310.16 copper ampacity (60/75/90°C) and AWG↔mm² equivalent cross-sectional area, for quick lookup without re-entering numbers.

AWG / kcmil	mm² Equiv.	60°C (Cu)	75°C (Cu)	90°C (Cu)

Copper, general ampacity per NEC Table 310.16, 30°C ambient, not more than 3 current-carrying conductors. Verify with a licensed electrician for your actual installation.

Cord & Signal Wire Reference (16 AWG–40 AWG) — these gauges fall outside NEC Table 310.16 (fixed branch-circuit wiring), which stops at 14 AWG. Flexible cord ampacity is governed by NEC Table 400.5 instead, and varies by cord construction (S, SJ, SJO, SO, etc.) — the calculator above does not use this table and does not accept these sizes as inputs. Geometry is standard AWG; check the cord's jacket marking or manufacturer spec for its actual ampacity rating.

AWG	Diameter	Area	Typical Use

Reference only — not part of this calculator's NEC 310.16-based ampacity or voltage-drop engine. Not a substitute for the cord's actual NEC Table 400.5 rating or manufacturer spec.

Frequently Asked Questions

How do I choose the right wire gauge?

Wire gauge selection has to satisfy two independent checks: the conductor's NEC ampacity rating must exceed the load current (with a 125% factor for continuous loads), and the voltage drop over the run's length must stay within the NEC-recommended 3% branch-circuit limit. This calculator checks both at once and recommends the smallest conductor that passes both tests.

What is the difference between AWG and mm²?

AWG (American Wire Gauge) is the North American wire sizing standard, where a lower number means a thicker wire. mm² (square millimeters) is the IEC metric standard used internationally, measuring cross-sectional area directly. Switching the Standard toggle converts your selected size to its closest cross-sectional-area equivalent in the other system.

What does a continuous load mean for wire sizing?

NEC 210.19(A)(1) requires conductors supplying a continuous load — one operating at maximum current for three hours or more — to be sized for 125% of that continuous current. The Continuous Duty toggle applies that factor to the ampacity check automatically.

Can I run multiple smaller conductors in parallel instead of one large one?

NEC 310.10(H) permits paralleling conductors 1/0 AWG and larger, provided all parallel sets are the same length, material, size, insulation, and terminations. Combine Conductors mode calculates the combined ampacity and shows the equivalent single conductor size for a given number of parallel runs.

Does temperature rating affect wire ampacity?

Yes. NEC Table 310.16 publishes separate ampacity columns for 60°C, 75°C, and 90°C conductor insulation. A higher temperature rating allows more current in the same physical wire size, but terminations are often only rated for 60°C or 75°C regardless of the conductor's own rating, so the lower of the two applies in practice.

Copper vs aluminum wire — which needs a smaller gauge?

Copper. For the same ampacity, aluminum conductors are typically sized about two AWG numbers larger than copper because aluminum has roughly 60% higher resistance and lower ampacity per cross-sectional area. Aluminum stays popular for large feeders due to its lower weight and cost per ampere of capacity — run both materials in the calculator to compare.