Wire Gauge Calculator

What this calculator does

The Wire Gauge Calculator provides fast estimates using standard electrical relationships. Enter Current (I), System Voltage, One-Way Distance to compute results for real-world electrical scenarios. Use it for quick checks, comparisons, and documentation while planning.

Inputs explained

  • Current (I): Electrical current in amperes (A).
  • System Voltage: Electrical potential difference in volts (V).
  • One-Way Distance: Value used by the calculator.
  • Max Voltage Drop: Electrical potential difference in volts (V).
  • Wire Material: Conductor material such as copper or aluminum.

How it works / Method

The calculator applies the listed formulas to the values you enter and then formats the result in standard units.

Formulas used

  • Uses NEC ampacity tables and voltage drop calculations

Units: I in amperes (A) V in volts (V)

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Wire Gauge Calculator

Calculate proper wire size (AWG)

A
V
ft
Result
—

NEC Ampacity (75°C)

AWGCopperAluminum
1420A—
1225A20A
1035A30A
850A40A
665A50A
485A65A
2115A90A

Common Applications

14 AWG: 15A circuits, lighting
12 AWG: 20A circuits, outlets
10 AWG: 30A circuits, dryers
8 AWG: 40A circuits, ranges
6 AWG: 50-60A, sub-panels

Related

Voltage DropConduit FillAmps to Watts

Step-by-step example

Scenario: 30A load, 100 feet, 3% drop max on 120V circuit.

Formula: Uses NEC ampacity tables and voltage drop calculations

  1. Required for 30A continuous: #10 AWG min
  2. Check 3% drop: Vdrop = 2xIxLxR/1000
  3. Result: #8 AWG recommended

Result: #8 AWG copper recommended

Use cases

  • Estimate conduit fill or voltage drop for planning.
  • Compare wire sizes and run lengths at a high level.
  • Document assumptions for preliminary layouts.
  • Create quick checks before code-compliant design.

Assumptions & limitations

  • Results are estimates and may be rounded; small differences are expected.
  • Inputs assume steady-state values; transient and surge effects are not modeled.
  • Voltage can vary by supply, load, and location; use measured values when possible.
  • Power factor varies by load type; use a realistic value for inductive equipment.
  • Wiring rules and safety codes vary by jurisdiction; consult a licensed electrician for installation decisions.

Sources & references

Related calculators

Frequently Asked Questions

The Wire Gauge Calculator provides a high-level estimate based on your inputs. It is useful for early planning and quick checks. Results depend on conductor type, length, and installation details. Codes vary by jurisdiction and installation method. Use this tool for planning, not final specifications. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

Follow the electrical code required in your location. NEC applies in the United States and IEC-based rules apply elsewhere. Codes include limits based on insulation, bundling, and temperature. This calculator cannot capture every rule or exception. Confirm results with the applicable code and a licensed professional. This calculator is intended for planning and comparison, not for final engineering approval.

Accuracy depends on how closely your inputs match the real installation. Conductor material and temperature affect resistance. Number of conductors and bundling affect allowable limits. Use measured lengths where possible. Treat the output as a planning estimate. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

The calculator assumes the voltage and power factor you provide. Utility voltage can vary throughout the day. Power factor can be lower for inductive equipment. Use conservative inputs if you are unsure. Verify with measured values for critical work. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

No. This tool is for education and early planning only. Final sizing must follow code and local inspection rules. Utility requirements and equipment ratings must be checked. Use a licensed electrician or engineer for installation decisions. Document assumptions for any preliminary estimates. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

Length, load current, and conductor size drive most outcomes. Conduit fill also depends on insulation type and conductor count. Small changes can alter the result noticeably. Double-check unit conversions and run length. Use measured values when possible. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.