# Wire Gauge Calculator Calculate the correct electrical wire gauge (AWG) for your circuit. Enter amps, voltage, and distance to get recommended wire size, voltage drop. ## What this calculates Choosing the correct wire gauge is critical for electrical safety and performance. Undersized wire causes excessive voltage drop, wasted energy, overheating, and potential fire hazards. This calculator determines the proper AWG wire size based on circuit amperage, voltage, distance, and acceptable voltage drop for copper and aluminum conductors. ## Inputs - **Circuit Amps** (A) — min 1, max 200 — Maximum current the circuit will carry - **Circuit Voltage** — options: 120V (standard outlets), 240V (appliances, HVAC) — System voltage for the circuit - **Wire Run Distance (one way)** (ft) — min 1, max 1000 — Distance from panel to load (one direction) - **Max Voltage Drop** (%) — min 1, max 10 — NEC recommends max 3% for branch circuits, 5% total - **Wire Material** — options: Copper, Aluminum — Copper is standard; aluminum is used for large feeders ## Outputs - **Recommended AWG** — formatted as text — Wire gauge that meets both ampacity and voltage drop requirements - **Wire Diameter** (mm) — Conductor diameter of the recommended gauge - **Max Amps for Gauge** (A) — Ampacity rating of the recommended wire gauge - **Actual Voltage Drop** (%) — Voltage drop at specified amps and distance - **Suggested Conduit** — formatted as text — Minimum conduit size for the recommended wire gauge ## Details Wire sizing must satisfy two requirements: ampacity (current-carrying capacity without overheating) and voltage drop (signal loss over distance). The NEC (National Electrical Code) sets ampacity limits for each gauge in various installation conditions. Voltage drop is calculated as Vd = 2 × L × I × R / 1000, where L is the one-way distance in feet, I is current in amps, and R is resistance per 1,000 feet. The NEC recommends maximum 3% voltage drop for branch circuits and 5% total voltage drop from the service entrance to the furthest outlet. Long wire runs to detached garages, workshops, or barn buildings often require upsizing the wire gauge to stay within voltage drop limits, even when the ampacity of a smaller wire would be sufficient. Copper wire is standard for most residential and commercial applications. Aluminum wire costs less per foot and is commonly used for large feeder circuits (100A+ service entrances, sub-panels) where the weight and cost savings are significant. Aluminum requires special connectors rated for aluminum and should never be connected to devices rated for copper only. ## Frequently Asked Questions **Q: What wire gauge do I need for a 20-amp circuit?** A: A 20-amp circuit requires minimum 12 AWG copper wire per the NEC. However, for runs over 50 feet, you may need to upsize to 10 AWG to keep voltage drop under 3%. Always check both ampacity and voltage drop for your specific run distance. **Q: What is acceptable voltage drop?** A: The NEC recommends maximum 3% voltage drop for branch circuits and 5% total from service entrance to the farthest outlet. For sensitive electronics, lower voltage drop (1-2%) is preferable. A 3% drop on a 120V circuit means only 116.4V reaches the load. **Q: When should I use aluminum wire instead of copper?** A: Aluminum wire is commonly used for large feeder circuits: service entrance cables (100A+), sub-panel feeds, and long-run heavy feeders where cost savings are significant. For 100A service, aluminum costs roughly half as much as copper. Aluminum requires AL-rated connectors and anti-oxidant compound at all connections. **Q: How do I calculate wire run distance?** A: Measure the distance from the electrical panel to the farthest outlet or device on the circuit. This is the one-way distance. The calculator accounts for the round-trip (multiplying by 2) automatically. Include vertical runs through walls and horizontal runs through attics or crawl spaces. --- Source: https://vastcalc.com/calculators/construction/wire-gauge Category: Construction Last updated: 2026-04-21