AWG to mm2 Voltage Drop Cable Sizing: NEC and IEC Crosswalk with Worked Examples

Compare AWG and metric conductors using their stated cross-sectional areas, resistance and temperature. A nearby metric size is a starting point for comparison, not an interchangeable installation rating.

TL;DR

Convert AWG to mm2 for communication, but calculate voltage drop from resistance.
Do not mix NEC ampacity tables with IEC installation assumptions.
10 AWG is 5.26 mm2; 6 mm2 is slightly larger and drops less voltage.
Use 3% branch and 5% feeder-plus-branch as common NEC design targets.
Aluminum needs a resistance check, not just a cross-sectional-area check.

American Wire Gauge is a logarithmic conductor-size system used mainly in North America. A square millimeter cable size is a metric cross-sectional area designation used in many IEC markets. Voltage drop is the voltage lost when load current flows through conductor impedance. Those three definitions matter because each one answers a different question: “what is the size called,” “how much metal is in the conductor,” and “how much voltage reaches the load.”

For background terminology, see American Wire Gauge and the International Electrotechnical Commission . In the field, the practical references are NEC 110.14(C) for terminal temperature limits, NEC 310.16 for conductor ampacity, the voltage-drop informational notes around NEC 210.19 and 215.2, and IEC 60364-5-52 for cable selection, installation method, correction factors, and voltage drop in IEC-style work.

Start With Resistance, Not the Name on the Cable

Voltage drop is controlled by current, path length, circuit type, conductor material, temperature, and impedance. The printed cable size is only a shortcut to the resistance value. If two cables have similar names but different resistance, the lower-resistance cable will deliver more voltage to the load. That is why a metric crosswalk should be used as a decision aid, not as a blind substitution chart.

85 ft example: 10 AWG copper, 120 V, 16 A and 85 ft one way. R = 1.24 Ω/kft, 75 °C; X = 0; PF = 1. ΔV = 2 × 16 × 85 × 1.24 / 1000 / 1 = 3.3728 V; 100 × 3.3728 / 120 ≈ 2.81067%. Check the margin for downstream circuits and the installation conditions.

On an IEC project, the same discipline applies with meters and ohms per kilometer. A 230 V, 20 A single-phase load 45 m from a distribution board sees the round-trip length of 90 m. A 4 mm2 copper cable may be serviceable for ampacity in one installation method, but a 6 mm2 cable often gives the cleaner voltage-drop result once grouping, ambient temperature, and future load are included. The label “roughly 10 AWG” does not decide that; the installed resistance and code context do.

Field scenario

For a metric pump circuit, obtain the manufacturer’s resistance and temperature basis before comparing sections. Review starting current and source impedance separately from the steady-state conductor loss.

Practical AWG and Metric Crosswalk

The table below is not an ampacity permission slip. It is a voltage-drop planning crosswalk that helps you choose which sizes to compare in the calculator. For final design, use the governing code, listed cable type, insulation temperature, terminals, raceway fill, grouping, and ambient correction. NEC Table 310.16 and IEC 60364-5-52 can produce different allowable currents for conductors with similar copper area because the installation assumptions are different.

Hypothetical calculations, not field measurements: the site RESISTANCE_DATA conductor values, referenced to 75°C. R is for one conductor; X = 0, power factor = 1, one set per phase unless the row states two sets. Equal parallel sets divide the result by the set count. L is one-way length. ΔV = 2 × I × L × R / 1000 for DC or single phase; use √3 instead of 2 and line-to-line voltage for balanced three phase. Pair feet with Ω/kft or meters with Ω/km. Drop (%) = 100 × ΔV / V. Only final table results are rounded to two decimals. Source impedance, contacts, unbalance and starting dynamics are excluded; ampacity and local installation requirements need separate review.

Scenario	Voltage / current	One way	Conductor	R / temperature	Model	Drop
100 ft AWG comparison	120 V / 16 A	100 ft	14 AWG Cu	3.14 Ω/kft; 75 °C	2; PF = 1	10.05 V / 8.37%
100 ft AWG comparison	120 V / 16 A	100 ft	12 AWG Cu	1.98 Ω/kft; 75 °C	2; PF = 1	6.34 V / 5.28%
100 ft AWG comparison	120 V / 16 A	100 ft	10 AWG Cu	1.24 Ω/kft; 75 °C	2; PF = 1	3.97 V / 3.31%
100 ft AWG comparison	120 V / 16 A	100 ft	8 AWG Cu	0.778 Ω/kft; 75 °C	2; PF = 1	2.49 V / 2.07%
100 ft AWG comparison	120 V / 16 A	100 ft	6 AWG Cu	0.491 Ω/kft; 75 °C	2; PF = 1	1.57 V / 1.31%
100 ft AWG comparison	120 V / 16 A	100 ft	4 AWG Cu	0.308 Ω/kft; 75 °C	2; PF = 1	0.99 V / 0.82%
85 ft example	120 V / 16 A	85 ft	10 AWG Cu	1.24 Ω/kft; 75 °C	2; PF = 1	3.37 V / 2.81%
95 ft receptacle	120 V / 16 A	95 ft	12 AWG Cu	1.98 Ω/kft; 75 °C	2; PF = 1	6.02 V / 5.02%
95 ft receptacle	120 V / 16 A	95 ft	10 AWG Cu	1.24 Ω/kft; 75 °C	2; PF = 1	3.77 V / 3.14%

Reproducible calculations

100 ft AWG comparison — 14 Cu (1)

100 ft AWG comparison: 14 AWG copper, 120 V, 16 A and 100 ft one way. R = 3.14 Ω/kft, 75 °C; X = 0; PF = 1. ΔV = 2 × 16 × 100 × 3.14 / 1000 / 1 = 10.048 V; 100 × 10.048 / 120 ≈ 8.37333%. Check the margin for downstream circuits and the installation conditions.

100 ft AWG comparison — 12 Cu (2)

100 ft AWG comparison: 12 AWG copper, 120 V, 16 A and 100 ft one way. R = 1.98 Ω/kft, 75 °C; X = 0; PF = 1. ΔV = 2 × 16 × 100 × 1.98 / 1000 / 1 = 6.336 V; 100 × 6.336 / 120 ≈ 5.28%. Check the margin for downstream circuits and the installation conditions.

100 ft AWG comparison — 10 Cu (3)

100 ft AWG comparison: 10 AWG copper, 120 V, 16 A and 100 ft one way. R = 1.24 Ω/kft, 75 °C; X = 0; PF = 1. ΔV = 2 × 16 × 100 × 1.24 / 1000 / 1 = 3.968 V; 100 × 3.968 / 120 ≈ 3.30667%. Check the margin for downstream circuits and the installation conditions.

100 ft AWG comparison — 8 Cu (4)

100 ft AWG comparison: 8 AWG copper, 120 V, 16 A and 100 ft one way. R = 0.778 Ω/kft, 75 °C; X = 0; PF = 1. ΔV = 2 × 16 × 100 × 0.778 / 1000 / 1 = 2.4896 V; 100 × 2.4896 / 120 ≈ 2.07467%. Check the margin for downstream circuits and the installation conditions.

100 ft AWG comparison — 6 Cu (5)

100 ft AWG comparison: 6 AWG copper, 120 V, 16 A and 100 ft one way. R = 0.491 Ω/kft, 75 °C; X = 0; PF = 1. ΔV = 2 × 16 × 100 × 0.491 / 1000 / 1 = 1.5712 V; 100 × 1.5712 / 120 ≈ 1.30933%. Check the margin for downstream circuits and the installation conditions.

100 ft AWG comparison — 4 Cu (6)

100 ft AWG comparison: 4 AWG copper, 120 V, 16 A and 100 ft one way. R = 0.308 Ω/kft, 75 °C; X = 0; PF = 1. ΔV = 2 × 16 × 100 × 0.308 / 1000 / 1 = 0.9856 V; 100 × 0.9856 / 120 ≈ 0.82133%. Check the margin for downstream circuits and the installation conditions.

85 ft example — 10 Cu (7)

95 ft receptacle — 12 Cu (8)

95 ft receptacle: 12 AWG copper, 120 V, 16 A and 95 ft one way. R = 1.98 Ω/kft, 75 °C; X = 0; PF = 1. ΔV = 2 × 16 × 95 × 1.98 / 1000 / 1 = 6.0192 V; 100 × 6.0192 / 120 ≈ 5.016%. Check the margin for downstream circuits and the installation conditions.

95 ft receptacle — 10 Cu (9)

95 ft receptacle: 10 AWG copper, 120 V, 16 A and 95 ft one way. R = 1.24 Ω/kft, 75 °C; X = 0; PF = 1. ΔV = 2 × 16 × 95 × 1.24 / 1000 / 1 = 3.7696 V; 100 × 3.7696 / 120 ≈ 3.14133%. Check the margin for downstream circuits and the installation conditions.

Copper, Aluminum, and the Area Trap

Copper and aluminum cannot be compared by area alone. Aluminum is lighter and often cheaper for feeders, but its conductivity is lower than copper. That means a 25 mm2 aluminum conductor does not behave like a 25 mm2 copper conductor for voltage drop. NEC work also brings termination compounds where required, connector ratings, and conductor material markings into the inspection path. IEC projects have the same engineering issue even when the paperwork looks different.

A practical rule is to calculate aluminum from its own resistance table, then compare the next two larger sizes before making a cost decision. For a long feeder, the cheapest installed option is not always the smallest allowed conductor. Labor, conduit size, lugs, voltage loss, heat, and future load all belong in the decision. On residential DIY work, aluminum branch-circuit conductors also bring extra termination concerns that should not be treated casually.

Calculator Workflow That Holds Up

Use actual load current. For receptacles, motors, EVSE, pumps, and heaters, distinguish design load from breaker size. A 20 A breaker does not mean every voltage-drop check should use 20 A.
Use one-way route length. The calculator handles circuit type, but your input length must be the real cable path, including vertical drops and panel offsets.
Compare the nearest sizes. If a chart says 10 AWG is near 6 mm2, compare both the smaller and larger practical metric options before choosing.
Finish with code checks. Verify NEC ampacity, terminal ratings, box fill, conduit fill, or IEC installation method after the voltage-drop result looks good.

FAQ

Is 10 AWG the same as 6 mm2 cable?

Not exactly. 10 AWG copper is about 5.26 mm2, while a 6 mm2 metric conductor is larger. For voltage drop, the 6 mm2 cable has lower resistance, but ampacity still depends on NEC 310.16 or IEC 60364 installation conditions.

Can I use mm2 area directly in a voltage drop calculator?

Yes if the calculator accepts metric cable area or conductor resistance. For this site, choose the nearest AWG/kcmil size or use the wire resistance calculator to compare ohms per 1000 ft against ohms per kilometer before sizing.

Which voltage drop target should I use with mixed NEC and IEC projects?

Use the project specification first. In NEC work, the common design target is 3% for a branch circuit and 5% combined feeder plus branch circuit. IEC 60364-5-52 commonly evaluates final circuits and distribution circuits by the allowed voltage drop in the national implementation.

Does a larger metric cable automatically pass NEC ampacity?

No. NEC ampacity depends on conductor material, insulation temperature, terminal temperature under NEC 110.14(C), ambient correction, and adjustment factors. A 16 mm2 cable may look larger than 6 AWG by area, but the listed cable type and termination rating still control.

How close is 2.5 mm2 to 14 AWG?

2.5 mm2 is about 20.2% larger (100 × (2.5 − 2.08) / 2.08) in copper area than 14 AWG, which is 2.08 mm2. That helps voltage drop, but it does not make the cable a substitute for a North American listed 15 A branch-circuit wiring method unless the installation rules permit it.

Should I convert aluminum cable by area or resistance?

Use the cable resistance at a stated temperature for voltage drop, then check cross-sectional area, ampacity and terminal compatibility separately. Do not assume equal copper and aluminum areas have equal resistance.

Run the Cross-Check Before You Pull Cable

Before you order cable or approve a substitution, run the load current, length, conductor material, and candidate AWG or mm2 sizes through the calculator. A five-minute comparison is cheaper than replacing a long feeder after equipment arrives on site.

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