Find the correct wire gauge (AWG or mm²) for any AC or DC circuit based on amperage, voltage, distance and allowable voltage drop — copper or aluminum.
Quick Answer: To calculate wire size, you need the load current (Amps), voltage, one-way distance, and allowable voltage drop (typically 3%). Thicker wire (lower AWG) is required for higher currents or longer distances to prevent voltage drop and overheating. Use the calculator below for instant results.
Electrical safety starts with the conductor. Wire that's too thin for its load has high electrical resistance, which generates heat — a leading cause of electrical fires. This calculator applies the standard voltage-drop sizing method used by electricians: given your load current, circuit voltage, one-way wire length, conductor material, and acceptable drop percentage, it finds the smallest wire that stays within safe limits.
Use this quick reference table to understand the maximum current-carrying capacity (ampacity) of common wire sizes. Never exceed these limits, even if voltage drop calculations suggest a smaller wire is acceptable.
| AWG Size | Cross-Section (mm²) | Max Ampacity (60°C) | Max Ampacity (75°C) | Typical Application |
|---|---|---|---|---|
| 14 AWG | 2.08 mm² | 15 A | 20 A | Lighting circuits, outlets |
| 12 AWG | 3.31 mm² | 20 A | 25 A | Kitchen outlets, general circuits |
| 10 AWG | 5.26 mm² | 30 A | 35 A | Dryers, water heaters, AC units |
| 8 AWG | 8.37 mm² | 40 A | 50 A | Ranges, sub-panels |
| 6 AWG | 13.3 mm² | 55 A | 65 A | Large sub-panels, EV chargers |
A 230V circuit carrying 20A over a 50 ft one-way copper run, at a 3% allowable drop, needs roughly 2.5mm² (about 12-13 AWG) to keep voltage loss under 7V. Halve the distance to 25 ft and the same load could safely run on a smaller conductor — distance, not just current, drives wire size on longer runs.
North America uses the American Wire Gauge (AWG) system, where — counterintuitively — a smaller number means a thicker wire. Most of the rest of the world sizes wire by cross-sectional area in mm². Here's how common sizes compare:
| AWG | Cross-Section | Typical Household Use |
|---|---|---|
| 18 AWG | 0.82 mm² | Low-voltage lighting, thermostats |
| 14 AWG | 2.08 mm² | 15A lighting circuits |
| 12 AWG | 3.31 mm² | 20A general outlets |
| 10 AWG | 5.26 mm² | 30A dryers, water heaters |
| 6 AWG | 13.3 mm² | Sub-panels, EV chargers |
| 2 AWG | 33.6 mm² | Main service entrance |
As current travels through a conductor, resistance causes voltage to fall — the longer the run, the greater the drop. Excessive drop shows up as dim lights, weaker motor performance, and wasted energy. This calculator solves for the minimum cross-section that keeps drop within your chosen percentage, for both copper and aluminum conductors.
Solar arrays, battery banks and other DC systems are especially sensitive to voltage drop because they run on low voltage and comparatively high current. Select 12V, 24V or 48V and enter your panel-to-controller or battery-to-inverter distance to size the conductor correctly — undersized DC wiring is one of the most common causes of underperforming solar installs.
For household 110V/230V circuits, three-phase 400V industrial feeds, or a sub-panel feeder, the same voltage-drop method applies — just with your system's actual voltage and current. Breaker sizing follows: the circuit breaker should be rated at or below the wire's ampacity, never above it, so the wire is always protected first.
Copper conducts better than aluminum, so it's the standard choice for household branch circuits. Aluminum is lighter and cheaper, which is why it's common for main service-entrance cables — but it needs a larger gauge than copper to carry the same current safely. Always tell the calculator which material you're using, since the required area differs meaningfully between the two.
Beyond raw gauge, the National Electrical Code accounts for insulation type and ambient temperature (THHN vs. Romex/NM-B have different temperature ratings), and requires a conduit fill calculation when multiple wires share a single pipe, to prevent heat buildup. This tool covers core gauge sizing; always confirm insulation type and conduit fill separately against your local code before installation.
Grounding and equipment-bonding conductors are sized differently from current-carrying conductors — NEC Table 250.66 covers grounding electrode conductors, and Table 250.122 covers equipment grounding conductors, both based on your main service or breaker size rather than the load-current method used here.
Electrical work is dangerous. Don't risk fires or failed inspections. Connect with a licensed local electrician for your project.
Find Local Electricians →Q: What happens if I use a 14 AWG wire for a 20 Amp circuit?
A: 14 AWG wire is rated for a maximum of 15 Amps. Using it for a 20-Amp circuit will cause the wire to overheat, potentially melting the insulation and causing a fire. Always use 12 AWG for 20-Amp circuits.
Q: Why does distance matter for wire size?
A: Every foot of wire adds resistance. On a long run (e.g., to a detached garage or pool pump), the cumulative resistance can drop the voltage below the device's requirements. This is why long runs require thicker wire.
Q: Is 2.5mm² wire the same as 14 AWG?
A: 2.5mm² is actually slightly thicker than 14 AWG (which is 2.08mm²). In metric regions, 2.5mm² is the standard for 20-Amp power sockets.
Q: Can I use solid wire and stranded wire together?
A: Yes, provided the gauge is the same. Stranded wire is more flexible and easier to pull through conduit, while solid wire is often preferred for terminating at devices (switches/outlets).
Q: Does aluminum wire need to be a different size than copper?
A: Yes — aluminum's lower conductivity means it typically needs to be one to two AWG sizes larger than copper to carry the same current safely.
Q: What voltage drop percentage should I use?
A: 3% is standard for branch circuits, 5% for a combined feeder-plus-branch run, and 1% for critical or sensitive electronics.
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