Free Tool

Free Cable Size & Wire Sizing Calculator

Enter amps, distance, and voltage to get recommended cable size and wire gauge instantly. NEC-compliant voltage drop calculation for copper and aluminum conductors.

Calculate Cable Size See Features
Cable size calculator showing recommended wire gauge and voltage drop results

Cable Sizing Made Simple

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Voltage Drop Calculator

Calculate voltage drop percentage for any cable run. Stay within NEC 3% branch circuit and 5% total limits.

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Cable Size Recommendations

Get recommended wire gauge and cable size based on load current, distance, and installation conditions.

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Copper vs Aluminum

Compare copper and aluminum cable sizes side by side. See how conductor material affects voltage drop and cost.

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Neutral Conductor Sizing

Size neutral conductors for non-linear loads with harmonic content. Handles 3-phase systems with unbalanced loads.

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Conduit Fill Calculator

Check NEC conduit fill limits. Calculate how many cables fit in EMT, IMC, or rigid conduit per Chapter 9 tables.

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Private & Offline

Runs in your browser. No account needed, no project data uploaded. Works offline after first load.

Cable Sizing Features

Wire Size Calculator With NEC Ampacity Tables

Enter load amps and get the minimum cable size per NEC Table 310.16. Supports 60°C, 75°C, and 90°C conductor temperature ratings with automatic derating for bundling and ambient temperature.

  • NEC Table 310.16 ampacity lookup
  • Temperature correction factors (Table 310.15(B)(1))
  • Bundling adjustment factors (Table 310.15(C)(1))
  • Continuous load 125% factor per 210.20(A)
Wire size calculator showing NEC ampacity results for different cable sizes

Voltage Drop Calculation for Long Cable Runs

Calculate exact voltage drop in volts and percentage for single-phase and three-phase circuits. Compare cable sizes to find the most economical option that stays within limits.

  • Single-phase and 3-phase voltage drop formulas
  • NEC 3% branch circuit / 5% total recommendations
  • Copper and aluminum conductor properties
  • Distance in feet or meters
Voltage drop calculation results showing percentage and volts for different wire gauges

Conduit Fill & Derating Helpers

Check NEC conduit fill percentages and apply derating factors for real installation conditions. Includes neutral conductor sizing for harmonic-rich loads.

  • EMT, IMC, rigid conduit fill per NEC Chapter 9
  • Derating for more than 3 current-carrying conductors
  • Neutral conductor sizing for non-linear loads
  • Cable size comparison across multiple scenarios
Conduit fill calculator showing conductor count and fill percentage

Cable Sizing FAQ

For a 30-amp circuit, you typically need 10 AWG copper or 8 AWG aluminum wire (per NEC Table 310.16 at 60°C). For long runs, you may need to upsize to limit voltage drop to 3%. Use the calculator above to check voltage drop for your specific distance.
A 50-amp circuit at 100 feet typically requires 6 AWG copper for ampacity, but voltage drop may require 4 AWG copper depending on voltage (120V vs 240V). At 240V single-phase, 6 AWG copper gives about 2.5% drop at 100 feet. Use the calculator to verify for your exact setup.
In practice, "cable sizing" and "wire sizing" refer to the same calculation — determining the correct conductor cross-section for a given load. "Wire size" (AWG gauge) is more common in North America, while "cable size" (mm²) is used internationally. This calculator supports both.
For most circuits, the neutral conductor is sized the same as the phase conductors. However, for 3-phase 4-wire systems with non-linear loads (computers, LED lighting, VFDs), triplen harmonics add on the neutral, requiring it to be oversized — sometimes up to 200% of phase conductor size. The calculator includes neutral sizing for these cases.
The NEC recommends (not requires) a maximum of 3% voltage drop for branch circuits and 5% total including feeder and branch circuit combined. Some applications (motor circuits, sensitive electronics) may need tighter limits. These are informational notes in NEC 210.19(A) and 215.2(A).
No — use it for estimation, planning, and sanity checks. Final designs must follow local codes (which may be stricter than NEC), project specifications, and professional review. Always consult a licensed electrician for installations.
A 200-amp service entrance typically requires 2/0 AWG copper or 4/0 AWG aluminum conductors. For long runs from the utility meter to the panel, voltage drop calculations may require larger conductors. Aluminum is common for service entrance because of cost savings at larger sizes.
No. The calculator runs entirely in your browser. No inputs, calculations, or project details are sent to any server. It works completely offline after the first page load.

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