Using the wire gauge calculator is straightforward. Enter your current load in amps, select your system voltage (120V, 240V, etc.), and input the one-way circuit length in feet from the power source to the load. Choose whether your system is single or three-phase, then click "Calculate Wire Size".

The calculator will determine the minimum wire size needed based on both ampacity (current-carrying capacity) and voltage drop considerations. This ensures your wire can safely handle the current while maintaining acceptable voltage levels at the load.

For best results, always use accurate measurements and consider environmental factors like ambient temperature, which can affect wire performance.

The calculator uses standard electrical units. Enter current in Amperes (A) - for example, "20" for a 20-amp circuit. Select voltage in Volts (V) from the dropdown menu, with common residential values being 120V and 240V.

For distance, enter the one-way length in feet for the AWG calculator or meters for the metric calculator. This is the distance from your electrical panel to the load, not the round-trip distance. The calculator automatically accounts for the return path.

⚠️ Important: Always use one-way distance, not the total wire length. If your panel is 50 feet from the outlet, enter 50 feet, not 100 feet.

Choose the calculator based on your location and electrical standards. Use the AWG Calculator if you're in the United States or Canada, following NEC (National Electrical Code) standards, or working with standard US voltages like 120V and 240V.

Use the Metric (mm²) Calculator if you're in Europe, Australia, or most other countries, following IEC standards, or working with metric voltages like 230V and 400V.

Both calculators provide accurate results for their respective standards, ensuring code compliance and safe installations in your region.

One-way distance is the length from your electrical panel to the load (device or outlet), measured along the wire path. This is what you should enter in the calculator. For example, if running wire from a basement panel to a second-floor outlet 50 feet away, you enter 50 feet.

Round-trip distance would be 100 feet (hot wire plus neutral return), but you don't need to calculate this. The calculator automatically accounts for the return path in its voltage drop calculations.

This is a common source of confusion - remember to only measure and enter the distance from point A to point B, not the total wire length you'll need to purchase.

The calculator uses two primary formulas to ensure safe wire sizing. First, it applies the voltage drop formula: VD = (2 × I × R × L) / 1000 for single phase, or VD = (√3 × I × R × L) / 1000 for three phase circuits, where VD is voltage drop, I is current, R is resistance, and L is length.

Second, it performs an ampacity check to verify the wire's current-carrying capacity exceeds your load, applying temperature derating factors based on ambient conditions. The calculator uses NEC Table 310.15(B)(16) for ampacity ratings.

The final recommendation is based on whichever requirement is more stringent - ensuring both voltage drop limits and ampacity requirements are satisfied for a safe, efficient installation.

The calculator provides highly accurate results based on NEC standards and industry-accepted formulas. It uses official ampacity ratings from NEC Table 310.15(B)(16) and resistance values from Chapter 9, Table 8 for copper conductors.

Results assume standard conditions: copper conductors, 75°C wire insulation rating, and proper temperature correction factors. These assumptions match most residential and commercial installations in North America.

While the calculator is accurate for typical installations, always verify results with local electrical codes and consult a licensed electrician for critical applications or unusual conditions.

Voltage drop is the reduction in voltage that occurs as electricity travels through a wire due to the wire's resistance. It's expressed as a percentage of the supply voltage. The NEC recommends limiting voltage drop to 3% for branch circuits and 5% total from service entrance to outlet.

Excessive voltage drop causes serious problems: motors run hot and inefficiently, lights dim or flicker, sensitive electronics malfunction, and equipment lifespan is reduced. For example, a motor receiving only 108V instead of 120V (10% drop) may overheat and fail prematurely.

Proper wire sizing prevents these issues by keeping voltage drop within acceptable limits, ensuring your electrical devices receive adequate voltage for optimal performance and longevity.

Ambient temperature significantly affects a wire's ampacity (current-carrying capacity). Higher temperatures reduce ampacity because wire insulation has temperature limits and electrical resistance increases with heat. At 86°F (30°C), wires carry their rated current, but at 104°F (40°C), they can only safely carry 91% of rated current.

For example, a wire rated for 20 amps at standard temperature can only carry 16.4 amps safely at 122°F (20A × 0.82 derating factor). This is critical in attics, near heating equipment, or in hot climates.

The calculator automatically applies these temperature correction factors, ensuring your wire sizing accounts for the actual installation environment and maintains safe operating temperatures.

Use this calculator for any electrical project where proper wire sizing is critical. Common residential applications include installing EV chargers, running power to outbuildings or workshops, adding sub-panels, wiring hot tubs or pools, and upgrading circuits for high-power appliances.

For commercial and industrial applications, the calculator helps with motor circuit wiring, long feeder runs, temporary power setups, solar panel connections, and equipment upgrades. It's especially valuable for projects with long wire runs where voltage drop becomes a significant concern.

Always verify your calculations with local electrical codes and have work inspected when required. The calculator provides a reliable starting point, but local requirements may vary.

Example 1 - EV Charger: For a 48A Level 2 charger (continuous load), you need a 60A circuit (48A × 125%). At 240V with a 75-foot run from the panel, the calculator recommends 6 AWG copper wire, which handles the current with only 1.5% voltage drop.

Example 2 - Detached Garage: Running a 50A sub-panel feed 150 feet underground at 240V requires 2 AWG copper to maintain acceptable 2.4% voltage drop. For a 30A RV outlet 100 feet from the panel at 120V, you'll need 8 AWG copper to stay within 2.5% voltage drop.

These examples show how distance dramatically affects wire sizing - the same 20A circuit might need 12 AWG at 50 feet but 6 AWG at 200 feet to maintain proper voltage.

Continuous loads (running 3+ hours) require special consideration per NEC Article 215.2. You must size both wire and breaker for 125% of the continuous load. For example, a 40A EV charger needs a 50A circuit (40A × 1.25 = 50A), and a 4000W heater on 240V draws 16.7A, requiring a 21A minimum circuit.

Common continuous loads include EV chargers, electric heaters, commercial lighting, outdoor signs and displays, and any equipment designed to run for extended periods. When using the calculator, enter the calculated 125% value as your current, not the actual load.

This safety factor prevents overheating and ensures reliable operation. Remember that both the wire and circuit breaker must be sized for the increased current.

Long wire runs require significantly larger wire sizes to prevent excessive voltage drop. For a 20A circuit at 120V maintaining 3% voltage drop: 50 feet requires 12 AWG, 100 feet needs 10 AWG, and 200 feet demands 6 AWG copper wire.

Key strategies for long runs include using higher voltage when possible (240V has half the voltage drop of 120V for the same power), considering aluminum wire for very long feeders (cheaper but requires larger size), and potentially installing a sub-panel closer to the loads.

The calculator accounts for these distance factors automatically, but understanding the relationship helps in planning. Every doubling of distance roughly requires going up two wire sizes to maintain the same voltage drop.

The most common error "Please fill in all required fields" occurs when missing essential inputs. Ensure you've entered the current load in amps, selected a voltage from the dropdown, and input the one-way circuit length. Double-check that you're entering numbers only - no units or text in the input fields.

If you see "No suitable wire size found", your requirements exceed standard wire sizes. This typically happens with very long runs or high currents. Try reducing circuit length by adding a sub-panel closer to the load, using 240V instead of 120V if possible, or splitting the load across multiple circuits.

Remember to use the correct units: current in amps (not watts), and one-way distance in feet (not the total wire length). For power in watts, divide by voltage to get amps.

Large wire recommendations usually result from long distances or low voltage. Voltage drop increases with length - a 20A circuit might need 12 AWG at 50 feet but 6 AWG at 200 feet. Similarly, 120V circuits have twice the voltage drop of 240V circuits for the same power.

To reduce wire size requirements: use 240V instead of 120V when possible, minimize circuit length by relocating panels or disconnects, accept 5% voltage drop for non-critical loads (instead of 3%), or consider aluminum wire for feeders which costs less despite needing larger sizes.

Remember that continuous loads require 125% sizing, and high ambient temperatures require derating. The calculator accounts for all these factors to ensure safe operation.

Basic NEC ampacity tables show current ratings for short runs under standard conditions. They don't account for voltage drop on longer runs. For example, 12 AWG is rated for 20A, but on a 150-foot run at 120V, it would have 7.5% voltage drop - far exceeding the 3% recommendation.

This calculator considers both ampacity AND voltage drop, plus temperature derating and actual circuit length. It recommends the larger of the two requirements, ensuring your installation meets code while maintaining proper voltage at the load.

Meeting minimum NEC ampacity requirements doesn't guarantee good performance. The calculator helps achieve both safety and optimal operation by preventing excessive voltage drop that can damage equipment and waste energy.

This wire gauge calculator is designed to find the correct wire size for new installations. It considers both ampacity (current-carrying capacity) AND voltage drop, recommends specific AWG or mm² sizes, includes temperature derating, and ensures your wire meets all safety requirements.

A voltage drop calculator serves a different purpose - it checks existing wire installations. You input a specific wire size and it calculates the resulting voltage drop and percentage loss, helping verify if your current wiring is adequate or troubleshoot voltage problems.

This calculator includes a voltage drop tab for checking existing installations, making it a comprehensive tool for both planning new circuits and verifying existing ones.

The calculator assumes copper conductors with 75°C insulation rating under standard installation conditions. For aluminum wire, you'll need approximately 2 AWG sizes larger. It doesn't account for bundled conductor derating (multiple wires in conduit), reactive loads or power factor, or special conditions like hazardous locations.

Special situations requiring additional consideration include motor starting currents (use 125-250% of running current), harmonic loads from electronic ballasts or VFDs, high-frequency circuits where skin effect matters, and voltage-sensitive equipment that may need less than 2% drop.

While the calculator works well for typical residential and commercial installations, always consult local codes and a licensed electrician for unusual conditions or critical applications.

The calculator assumes copper wire, which offers smaller size for the same ampacity, better conductivity, and easier connections, but costs 2-3 times more than aluminum and is heavier. Copper is standard for branch circuits and most residential wiring.

Aluminum wire is economical for large feeders and long runs. It costs less and weighs less, but requires approximately 2 AWG sizes larger than copper and needs special AL-rated connectors. For example, if the calculator shows 6 AWG copper, you'd use 4 AWG aluminum.

Use aluminum only for service entrance cables and sub-panel feeders. Never use aluminum for branch circuits or receptacles unless specifically designed for it. Always use anti-oxidant compound on aluminum connections.