Wire Gauge Calculator
Free wire gauge calculator. Enter AWG or mm², wire length, current, and material to calculate resistance, voltage drop, power loss, and ampacity rating.
Calculate wire resistance, voltage drop, and ampacity for AWG/mm² sizes.
What is Wire Gauge?
Wire gauge refers to the physical diameter or cross-sectional area of an electrical conductor. Two primary systems exist: American Wire Gauge (AWG) and metric millimetres squared (mm²). AWG numbers decrease as wire thickness increases — for example, 24 AWG is much thinner than 12 AWG. This calculator converts between AWG and mm², and computes key electrical properties like resistance, voltage drop, and safe current capacity based on conductor material and circuit length.
The AWG system originated in the 1850s and remains standard in North America. IEC 60228, the metric equivalent, is used worldwide and defines copper and aluminum conductor sizes.
Why Does Wire Size Matter?
Improper wire sizing causes several serious problems:
- Voltage drop: Resistive losses reduce the voltage available at the load, affecting device performance
- Power loss: Resistive heating wastes energy as heat, reducing efficiency
- Safety: Oversized currents in undersized wire cause overheating, insulation breakdown, and fire risk
- Efficiency: Undersized distribution lines lose kilowatts across long runs (solar systems, remote power)
Electrical codes in most countries enforce maximum voltage drop limits (typically 3% for branch circuits, 5% overall). This calculator helps you select wire sizes that comply and operate safely.
The Physics Behind It
Wire resistance follows Ohm’s law: R = ρL/A
Where:
- R = resistance (Ω)
- ρ (rho) = resistivity of the material (Ω·mm²/m) — copper ≈ 0.0172, aluminum ≈ 0.0282
- L = conductor length (m)
- A = cross-sectional area (mm²)
Voltage drop: V = IR (in DC; AC includes impedance effects)
Power loss: P = I²R (dominant heating mechanism)
Ampacity (safe continuous current) is empirically determined from wire tables and depends on insulation type, installation method, and ambient temperature. This calculator uses conservative values per IEC 60364.
How to Use
- Select size unit: Choose AWG (American standard) or mm² (metric). The calculator auto-converts between them.
- Enter wire gauge: If AWG, pick 0–40. If mm², enter the cross-section (e.g., 2.5, 4, 6, 10 mm²).
- Enter one-way length: Specify the distance the wire runs. For a circuit with outbound and return paths, enter just the outbound distance; voltage drop naturally accounts for the round trip.
- Enter current: The steady-state current (in amps) flowing through the wire.
- Select material: Copper conducts better (lower resistivity) than aluminum but costs more. Aluminum requires larger gauges for equivalent ampacity.
- Choose frequency: DC (direct current) or AC (50/60 Hz). AC adds a ~5% penalty due to skin effect — at high frequencies, current hugs the wire surface, increasing effective resistance.
- Review results: The calculator outputs cross-section, equivalent gauge, resistance, voltage drop, power loss, and maximum safe ampacity.
Examples
Example 1: Home circuit (12 AWG, 15 A branch)
Input:
- Size: 12 AWG
- Length: 25 m (one-way distance from breaker to outlet)
- Current: 15 A
- Material: Copper
- Frequency: AC 60 Hz
Result:
- Resistance: ~0.207 Ω
- Voltage drop: ~3.1 V (acceptable at 120 V outlet)
- Ampacity: >20 A ✓ safe for 15 A circuit
Example 2: Solar PV system (100 m copper run, 50 A)
Input:
- Size: 10 mm²
- Length: 100 m (DC from panels to controller)
- Current: 50 A
- Material: Copper
- Frequency: DC
Result:
- Resistance: 0.172 Ω
- Voltage drop: ~8.6 V (problematic at 48 V — ~18% drop)
- Recommendation: Increase to 16 mm² (4 AWG) for <5% drop
Example 3: Industrial feeder (4/0 AWG aluminum, 30 A, 50 m)
Input:
- Size: 4/0 AWG (≈107 mm²)
- Length: 50 m
- Current: 30 A
- Material: Aluminum
- Frequency: AC 60 Hz
Result:
- Voltage drop: ~2.4 V (acceptable)
- Power loss: ~27.2 W
- Ampacity: >700 A ✓ heavily overspecified (but common in distribution)
Frequently Asked Questions
Q: What’s the difference between AWG and mm²? A: AWG (American Wire Gauge) is the legacy North American standard. mm² (millimetres squared) is the metric standard used internationally. They measure the same thing — conductor cross-sectional area — but use different scales. This calculator converts between them instantly.
Q: How do I know the correct wire size for my project? A: Start with the circuit ampacity requirement (max current), then check local electrical codes for voltage drop limits (typically ≤3% for branch circuits). Use this calculator to find the smallest gauge that keeps voltage drop within limits while exceeding ampacity. Consult a licensed electrician for safety-critical installations.
Q: Why does aluminum require larger sizes than copper? A: Aluminum has about 1.6× higher resistivity than copper. At equivalent current, aluminum wire dissipates more heat. To match copper’s voltage drop, you need ~1.5–2 times the cross-sectional area.
Q: What is skin effect? A: At high AC frequencies, the electromagnetic field pushes current toward the conductor surface. This reduces effective cross-section and increases resistance by 5–15% depending on frequency and wire size. This calculator conservatively adds 5% for all AC cases.
Q: Does insulation thickness affect voltage drop? A: No. Voltage drop depends only on the copper/aluminum core, not the plastic jacket. Insulation affects ampacity (higher-temperature ratings allow more current) and mechanical protection, but not electrical resistance.
Q: Can I use one wire for both outbound and return? A: In DC systems, you often run separate outbound and return. In AC systems (residential/commercial), the return current flows through a separate conductor (neutral or return wire) or the ground. Always measure length as one-way; the calculator assumes this convention.