AWG ↔ mm² • Ampacity & Voltage Drop
Convert AWG to mm and mm², check ampacity (with bundling derating), compute voltage drop with temperature/material, and compare gauges visually. Includes exportable reference table.
🚀 Quick Actions
All tabs share the same state — change values anywhere and it propagates.
Results
Diameter: mm
Area: mm²
Resistance: Ω/km
Ampacity (Chassis): A
Ampacity (Power Transmission): A
Adjusted Ampacity (bundling/custom): —
Rough NEC-style derating
Overrides automatic rule if set
These settings affect safety (ampacity). Voltage Drop uses material & temperature separately. Derating used: —%
Closest AWG Match: ---
Cu≈1.724e-8, Al≈2.82e-8
Cu≈0.00393, Al≈0.00403
Voltage Drop: --- V (---%)
Adjusted ρ at temperature: — Ω·m
Load vs adjusted ampacity: — (I=— A / Adj Amp=— A)
Warning: Current exceeds adjusted ampacity for this gauge (thermal risk).
Based on the voltage, current, length, and material settings above, find the smallest wire gauge that keeps the voltage drop below your target.
Label 1: —
Label 2: —
| AWG | Diameter (mm) | Area (mm²) | Resistance (Ω/km) | Ampacity (Chassis) | Ampacity (Power) |
|---|
📚 Notes & References
Formulas
dₙ = 0.127 · 92^((36−n)/39) (mm)
Aₙ = (π/4) · dₙ² (mm²)
Standards
- ASTM B258 — wire dimensions
- NFPA 70 (NEC) — ampacity tables
Important
- Voltage drop uses material & temperature — bundling affects ampacity (safety), not Vdrop directly.
- Long runs: Vdrop can dominate over ampacity.
- PCB traces need a different calculator.
📘 Understanding AWG, Ampacity & Voltage Drop
American Wire Gauge (AWG) is a standardized system (mostly US) for round conductors. The higher the AWG number, the thinner the wire. Historically this follows the number of drawing steps required to reach the final size.
AWG → Diameter / Cross-Section (mm & mm²)
For gauge n:
- Diameter (mm):
dₙ = 0.127 × 92^((36 − n)/39) - Area (mm²):
Aₙ = (π/4) × dₙ²
Note: the table used in this tool reflects common reference values (Cu ≈ 20 °C) to avoid runtime rounding drift.
Ampacity — Chassis vs Power Transmission
Ampacity is the continuous current a conductor can carry without exceeding its temperature rating (conductor + insulation + environment). Thermal dissipation is key:
- Chassis wiring — short runs, open air, spaced wires ⇒ better convection ⇒ higher allowable current.
- Power transmission / conduits — long runs, grouped/bundled cables ⇒ heat trapped ⇒ lower ampacity.
“Chassis/Power” values here are reference. For real installations, apply your local code tables & factors (e.g., NEC).
Bundling / Derating
When multiple current-carrying conductors are bundled (harness, loom, conduit), heat removal is poorer. Apply a derating factor to nominal ampacity. In the tool, Bundled Conductors and Custom Derating adjust the safety ampacity (shown as an indicator in the Voltage Drop tab).
Why doesn’t derating change voltage drop?
Voltage drop is pure Ohm’s law: Vdrop = I × R. For a given area and material,
R depends on resistivity (and thus temperature/material), not on whether a code allows you to
run more or less current. Derating is a thermal/safety constraint, not a change to Ohm’s law.
That’s why the tool shows derating as an ampacity diagnostic alongside (but separate from) the drop calculation.
Voltage Drop
For length L, Vdrop = I × R_total with
R_total = R_line × L (one-way) or 2 × R_line × L (round-trip).
The linear resistance R_line varies with material resistivity ρ and temperature:
- Temperature dependence:
ρ(T) = ρ₍20 °C₎ × [1 + α × (T − 20)] -
The Ω/km table is for Cu ≈ 20 °C. The tool rescales it by the ratio
ρ(T) / ρ_Cu@20 °Cand respects the chosen material (Cu/Al/Custom).
At DC/50–60 Hz, skin effect is negligible for these sizes and can be ignored.
Materials, Stranding, Insulation
- Copper vs Aluminum — Al has higher resistivity (~1.6× Cu), so for the same drop you need a larger area.
- Solid vs stranded — bulk resistivity is essentially the same; stranded is about flexibility and terminations.
- Insulation & temperature class (60/75/90 °C…) — limits ampacity, not Ohm’s law.
Practical selection workflow
- Check ampacity (apply bundling derate if needed).
- Check acceptable voltage drop at the load (e.g., <3 % for low-voltage DC lines).
- Pick the AWG that satisfies both.
⚠️ Disclaimer
This tool provides reference values. For real installations, comply with applicable codes/standards (NEC, etc.), consider insulation rating, ambient temperatures, number of current-carrying conductors in the same pathway, and environmental conditions.