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Wire Size Calculator

Calculate the right wire size (SQ) using KEC standard formulas. Supports single-phase and three-phase systems.

One-way distance from panel to load

KEC: feeder 2% + branch 2% = 4% total

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What is the Wire Size Calculator?

The Wire Size Calculator helps electrical workers instantly determine the correct wire gauge (SQ) based on load current, cable length, and voltage system type โ€” using KEC standard voltage drop constants. The calculator automatically selects the correct K constant for each wiring method: K=35.6 for single-phase 2-wire, K=30.8 for 3-phase 3-wire, and K=17.8 for single-phase 3-wire and 3-phase 4-wire circuits. For 3-phase 4-wire 380V systems, the voltage drop base is correctly set to the phase voltage (220V) rather than the line voltage (380V), preventing the overestimation error common with simplified calculations. The tool simultaneously calculates the minimum wire size by ampacity (to prevent overheating) and by voltage drop (to ensure equipment performance), then recommends the larger of the two. Results include an always-visible ampacity disclaimer noting that the values assume single-core, open-air installation โ€” the most favorable condition โ€” and that bundled or conduit-installed wiring may require derating by 30% or more. kW-to-ampere conversion is built in with an adjustable power factor slider. CV cable, HIV, and HFIX wire ampacity tables are all supported. All calculations run client-side with no server required.

Common Use Cases

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Distribution Panel Feeder Sizing
Quickly size the feeder wire from a distribution panel to each load by entering the load current and one-way cable distance โ€” K constants are applied automatically for the selected voltage system.
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Three-Phase Motor Wiring
Enter kW capacity and distance for air conditioners, motors, or pumps on 3-phase circuits and let the calculator select the right K constant and base voltage automatically.
๐Ÿ”
Existing Wiring Adequacy Check
Verify whether currently installed wire sizes are adequate for the actual load by entering the existing current and cable length โ€” see the real voltage drop percentage and compare against KEC limits.
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On-Site Design Change Response
When loads are added or cable routes change on-site, use this tool on your phone to get an immediate size recommendation before a formal design review โ€” with copy-to-clipboard for quick sharing.

How to Use

  1. 1
    Select voltage system
    Choose the circuit type from the dropdown: single-phase 2-wire, single-phase 3-wire, 3-phase 3-wire (220V or 380V), or 3-phase 4-wire 380V. The K constant and base voltage are automatically set for all downstream calculations.
  2. 2
    Enter load
    Type the load current in amperes directly, or switch to kW mode and enter the equipment capacity with power factor to get the auto-converted current. Use the nameplate current or design specification as your reference.
  3. 3
    Enter cable conditions
    Enter the one-way cable distance in meters from the panel to the load, select the allowed voltage drop percentage (2% for precision equipment, 3% for general power, 5% for lighting), and choose the wire insulation type.
  4. 4
    Review and apply results
    Check the recommended SQ and the two basis cards showing which criterion was decisive. Read the ampacity disclaimer and verify the final wire size with a qualified engineer before procurement and installation.

Frequently Asked Questions