Wire Gauge Calculator⚡
Calculate the correct electrical wire size based on current, distance, voltage drop, conductor material, and NEC derating factors.
This wire gauge calculator supports AWG and metric wire sizes and helps electricians, engineers, and DIY users choose the safest cable size for their circuits.
Dual-check calculation for NEC Ampacity and Voltage Drop requirements.
| Ampacity Requirement | -- AWG |
|---|---|
| Voltage Drop Requirement | -- AWG |
| Final Selected | -- AWG |
| Voltage Drop | 0.00 V |
|---|---|
| Voltage Drop % | 0.00 % |
| Voltage at End | 0.00 V |
| Material | Recommended Wire | Est. Drop % |
|---|
| Wire Size | Drop % | Voltage Lost | Status |
|---|
How to Calculate Wire Gauge
Sizing electrical wire correctly is critical for both safety and performance. A proper wire gauge calculator must execute a Dual-Check System. First, it determines the Ampacity Requirement to ensure the wire will not overheat and melt under the required load. Second, it calculates the Voltage Drop Requirement to ensure the equipment at the end of the wire receives enough voltage to operate efficiently. The calculator must select whichever wire gauge is larger between these two tests.
Wire Gauge Formula Explained
The standard professional formulas used to calculate both variables are based directly on the National Electrical Code (NEC):
- Corrected Ampacity: Required Current = (Load Current × Safety Factor) / (Temperature Factor × Conduit Fill Factor)
- DC & Single-Phase AC Voltage Drop: VD = (2 × Length × Current × Resistance) / 1000
- Three-Phase AC Voltage Drop: VD = (1.732 × Length × Current × Resistance) / 1000
Once Voltage Drop (VD) is calculated, you find the percentage by dividing the VD by the source voltage and multiplying by 100.
Ampacity vs Voltage Drop
Ampacity is purely a safety constraint. It defines the maximum amount of electrical current a wire can carry before its insulation begins to melt, which is a severe fire hazard. Voltage Drop is a performance and efficiency constraint. As power travels over long distances, wire resistance causes voltage to "leak" away as heat. If the voltage drops too low, electronics may shut down, and motors will pull excess current, causing them to overheat and fail prematurely.
Copper vs Aluminum Wire Size
The material of your conductor significantly impacts the required wire size. Copper is an exceptional conductor with very low electrical resistance, allowing you to use a thinner wire gauge for heavy loads. Aluminum has higher resistance and is less conductive, but it is vastly lighter and less expensive. As a general rule in the electrical industry, if you switch from a copper wire to an aluminum wire, you must upsize the wire by one or two full gauge sizes to handle the identical ampacity and maintain the same voltage drop limit.
Single Phase vs Three Phase Wire Sizing
The type of power system you are running alters how voltage drops over a distance. In a standard Single-Phase circuit (like a 120V residential outlet), power must travel down the hot wire and all the way back via the neutral wire, which is why the formula uses a multiplier of 2. In a Three-Phase circuit, the power delivery is staggered across three wires, making it much more efficient. As a result, the calculation uses a smaller multiplier of 1.732 (the square root of 3), meaning you can often use a slightly smaller wire size for 3-phase equipment than you could for single-phase equipment of the same amperage.
Wire Gauge Chart (AWG to mm²)
While the United States and North America use the American Wire Gauge (AWG) system, most of the rest of the world uses cross-sectional area measured in square millimeters (mm²). Here is a quick reference conversion chart for standard sizes:
| American Wire Gauge (AWG) | Metric Equivalent (Approx. mm²) | Max Copper Ampacity (75°C) |
|---|---|---|
| 14 AWG | 2.08 mm² | 20 Amps |
| 12 AWG | 3.31 mm² | 25 Amps |
| 10 AWG | 5.26 mm² | 35 Amps |
| 8 AWG | 8.37 mm² | 50 Amps |
| 6 AWG | 13.3 mm² | 65 Amps |
| 4 AWG | 21.2 mm² | 85 Amps |
What Wire Size Do I Need?
The exact wire size you need depends entirely on your specific parameters. For a short, 15-Amp household lighting circuit, a 14 AWG copper wire is perfectly adequate. However, if you are running a 50-Amp Subpanel feeder line 150 feet out to a detached garage, you must account for the severe voltage drop over that distance, which may force you to use a heavy-duty 4 AWG or 2 AWG wire to remain within the safe 3% NEC limit. Always use a dual-check wire gauge calculator to verify your exact needs before purchasing wire.
Free Professional Wire Gauge Calculator (AWG & mm²)
Sizing electrical wire correctly is the most critical step in ensuring equipment runs safely and efficiently. If a wire is too small, it can overheat and cause a fire, or create excessive voltage drop that damages your devices. Our professional Wire Gauge Calculator uses a robust "Dual-Check System" to instantly find the perfect AWG and mm² wire size by satisfying both your specific voltage drop limits and strict National Electrical Code (NEC) ampacity derating requirements.
How to Use the Calculator
- Start with Presets (Optional): Click on a quick preset (like Residential Circuit, Subpanel Feeder, or EV Charger) to instantly load common industry-standard parameters.
- Enter Core Circuit Requirements: Input your load current (in Amps), the supply voltage at the breaker panel, and the one-way cable length. The calculator automatically accounts for the round-trip return path in its math.
- Set Limits & Materials: The default and highly recommended voltage drop standard is 3%. Choose between Copper or Aluminum, and select your electrical phase (DC, 1-Phase, or 3-Phase).
- Apply Advanced NEC Derating: Click "Advanced NEC Derating Factors" to adjust for hot ambient temperatures, multiple current-carrying wires in the same conduit, continuous loads (running >3 hours), or parallel conductor runs.
- Analyze the Dual-Check Results: The tool instantly evaluates the minimum wire needed for Ampacity versus the minimum wire needed for Voltage Drop, and recommends the safest, thickest option.
- Simulate & Compare: Use the dynamically generated Alternative Sizes table, Copper vs. Aluminum comparison, and Quick Simulation buttons (e.g., "Try Next Larger Wire", "Target 2.0% Drop") to instantly see how different choices affect your performance.
- Export: Click "Show Engineering Details" to verify the background math, or click "Copy Full Report" to easily paste your project specs into an email, spreadsheet, or document.