AWG Wire Size Calculator — Gauge to mm, Ampacity & Voltage Drop | CalcEngines
Electronics Calculators

AWG Wire Size Calculator

Convert American Wire Gauge sizes to diameter, cross-sectional area, resistance, and current capacity. Includes voltage drop analysis for complete wire sizing.

AWG Wire Size Calculator
Copper conductor — real-time analysis
LIVE
Select AWG Size
Quick Select
Physical Dimensions
Diameter
—
millimeters (mm)
Diameter
—
inches (in)
Area
—
mm² cross-section
Area
—
kcmil
Electrical Specs (Copper)
Ω
DC Resistance
—
per km at 20°C
⚡
Max Ampacity
—
chassis wiring (free air)
Ampacity Rating
Moderate
0 A — 400 A
📦 Typical use: —
Cross-Section Visualization
Cross Section
AWG 10 r
Size Comparison
Circuit Parameters
A
m
V
°C
Voltage Drop
—
Volts (V)
Drop %
—
% of supply
Power Loss
—
Watts (W)
Enter your circuit parameters above to see voltage drop analysis.
Wire Resistance
—
Total loop resistance (×2 length)
Temp Correction
—
Resistance at selected temp
AWGDia (mm)Dia (in)Area (mm²)Resist. (Ω/km)AmpacityTypical Use

* Chassis wiring ampacity (free air, 60°C insulation). Conduit / power transmission ratings are lower. Highlighted row = currently selected gauge.

Diameter
d = 0.127 × 92^((36−n)/39)
n is the AWG number. For 4/0 use n = −3, for 3/0 use n = −2, etc. Result is in millimeters.
Cross-Section Area
A = (π/4) × d²
Area in mm². Fundamental for current capacity and resistance calculations.
DC Resistance
R = (ρ × L) / A
ρ (copper) = 1.68 × 10⁻⁸ Ω·m at 20°C. L in meters, A in m². Result in ohms.
Temp Correction
R_T = R₂₀ × [1 + α(T−20)]
α (copper) ≈ 0.00393 /°C. T is temperature in °C. Resistance rises with temperature.
Voltage Drop
V_drop = I × R_total
R_total = 2 × R (both conductors in loop). I is load current in amps.
AWG Rule of Thumb
+3 AWG → ½ Area
Every 3 gauge increase halves the cross-section. Every 6 gauge increase reduces area by 4×. Higher AWG = thinner wire.

How to Use the AWG Wire Size Calculator

Select any American Wire Gauge from AWG 4/0 (the thickest, at 11.68 mm diameter) through AWG 40 (ultrafine magnet wire at 0.08 mm). The calculator instantly shows the conductor diameter in both millimeters and inches, cross-sectional area in mm² and kcmil, DC resistance per kilometre at 20°C, and the maximum continuous current rating for copper in free air.

Use the Voltage Drop tab to check whether your chosen gauge is suitable for a specific circuit. Enter the load current, one-way wire length, supply voltage, and operating temperature. The calculator applies the correct temperature coefficient for copper (α = 0.00393 /°C) and flags whether the drop exceeds the 3% NEC recommendation or the 5% maximum.

Rule of thumb: Every 3 AWG steps doubles the cross-sectional area and halves the resistance. Every 6 AWG steps increases the area by 4×. Lower AWG number = thicker wire = more current capacity.

AWG to mm² Conversion — Common Equivalents

The AWG system and the IEC mm² system are both used worldwide — AWG in North America, mm² in Europe and most of Asia. These are the most common equivalents used in engineering:

AWG 14 ≈ 2.5 mm² (household branch circuits, 15 A) · AWG 12 ≈ 4 mm² (20 A outlets) · AWG 10 ≈ 6 mm² (30 A circuits, A/C units) · AWG 8 ≈ 10 mm² (dryer circuits, HVAC) · AWG 6 ≈ 16 mm² (sub-panels, EV chargers) · AWG 4 ≈ 25 mm² (feeder circuits) · AWG 2 ≈ 35 mm² (large feeders) · AWG 1/0 ≈ 50 mm² (service entrance).

These are approximate — use the calculator for exact values. The conversion formula is: Area (mm²) = π/4 × diameter² where diameter = 0.127 × 92^((36−n)/39) mm.

Voltage Drop Guidelines

Excessive voltage drop causes motors to run hot, LED drivers to malfunction, and sensitive electronics to behave erratically. The NEC recommends a maximum 3% voltage drop on branch circuits and no more than 5% total including the feeder. For DC systems (automotive, solar, telecommunications), 2–3% is the standard target.

The key variables are wire length and current — doubling either doubles the voltage drop. To reduce drop: use a heavier gauge (lower AWG number), shorten the run, increase the system voltage, or run multiple conductors in parallel. The voltage drop formula is V_drop = I × 2L × R/km / 1000, where 2L accounts for both the supply and return conductors.

Frequently Asked Questions

How do I convert AWG to mm?
Use the formula: diameter (mm) = 0.127 × 92^((36 − n) / 39), where n is the AWG number. For 4/0 use n = −3, for 3/0 use n = −2, for 2/0 use n = −1, for 1/0 use n = 0. Examples: AWG 10 = 2.588 mm, AWG 14 = 1.628 mm, AWG 22 = 0.644 mm. Every 6 AWG steps halves the diameter.
What AWG wire do I need for a 20 amp circuit?
For a standard 120/240 V household 20 A circuit, NEC requires AWG 12 (minimum). For automotive or DC systems at 20 A with short runs (under 2 m), AWG 14 may suffice — use the voltage drop calculator to verify. For continuous loads, derate the wire to 80% of its ampacity, so AWG 12 (41 A rated) is the correct minimum for a 20 A continuous circuit.
What is the difference between AWG and mm²?
AWG (American Wire Gauge) is the North American standard, where a higher number means a thinner wire. mm² (IEC 60228) is the international standard based on cross-sectional area. Common equivalents: AWG 14 ≈ 2.5 mm², AWG 12 ≈ 4 mm², AWG 10 ≈ 6 mm², AWG 8 ≈ 10 mm², AWG 6 ≈ 16 mm². The two systems are not exactly interchangeable — always verify with the manufacturer’s datasheet.
Why does wire resistance increase with temperature?
Higher temperatures cause increased lattice vibration in the copper crystal structure, making it harder for electrons to flow. Copper’s resistance increases by approximately 0.393% per degree Celsius above 20°C (temperature coefficient α = 0.00393 /°C). A wire running at 75°C has about 22% higher resistance than its 20°C rated value, which is why ampacity ratings specify an insulation temperature class.
Values are theoretical / standard estimates for annealed copper at 20°C. Always verify with manufacturer datasheets and applicable electrical codes (NEC, IEC 60228, etc.) for safety-critical installations.
CalcEngines.com — Free Engineering Calculators