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Wire Size Calculator (AWG & mm²)

Calculate recommended minimum conductor gauge and cross-sectional area to keep voltage drop within allowable limits.

1. Enter your numbers  →  2. Check the answer  →  3. Read the steps before you trust it

V
A

Recommended Conductor Gauge

Recommended AWG Size
12 AWG

Nominal Area: 3.31 mm² (Min required: 3.28 mm²)

Estimated Voltage Drop
3.5732 V (2.9777%)
Voltage at Load
116.427V
Target Max Allowed Drop
3.6V

Step-by-Step Engineering Calculation

  1. 1Length: L=75 feet=22.860 mL = 75\text{ feet} = 22.860\text{ m}
  2. 2Max allowable drop: 3% of 120 V=3.600 V3\%\text{ of }120\text{ V} = \mathbf{3.600\text{ V}}
  3. 3Conductor material: COPPER (ρT at 20∘C=1.7241e−8 Ω⋅m\rho_T\text{ at }20^\circ\text{C} = 1.7241e-8\ \Omega\cdot\text{m})
  4. 4Min required area: Amin=Amin=2×ρ×L×IΔVmax=3.284 mm2A_{\text{min}} = A_{\text{min}} = \frac{2 \times \rho \times L \times I}{\Delta V_{\text{max}}} = \mathbf{3.284\text{ mm}^2}
  5. 5Recommended standard gauge: 12 AWG (Nominal Area =3.31 mm2= 3.31\text{ mm}^2)
  6. 6Actual estimated voltage drop: ΔV=3.573 V\Delta V = \mathbf{3.573\text{ V}} (2.98%2.98\%)
  7. 7Estimated voltage at load: Vload=116.427 VV_{\text{load}} = \mathbf{116.427\text{ V}}

Formula & Theory

A_min = (Multiplier × ρ × L × I) / ΔV_max

Calculates the minimum required cross-sectional conductor area (mm² and AWG) to ensure circuit voltage drop stays below the target threshold.

Variable Definitions
A_min:
Minimum Area (mm² / kcmil) – Minimum required cross-sectional conductor area
AWG:
Gauge (AWG) – Recommended American Wire Gauge
ΔV_max:
Max Drop (Volts (V)) – Maximum allowable voltage drop

Worked Engineering Example

24V Off-Grid Solar Battery Cable Run

A 24V DC inverter circuit pulling 40A over 20 feet with a 2% allowed voltage drop.

Inputs:
  • Voltage: 24 V
  • Current: 40 A
  • Length: 20 ft
  • Max Drop: 2%
Result: Recommended: 4 AWG Copper (Actual Drop: 1.66%, 0.40V)

Key Assumptions

  • •Pure conductor resistance sizing based on allowed voltage drop.

Limitations & Safety Scope

  • •Thermal ampacity derating (insulation class 60°C/75°C/90°C, ambient temperature, conduit fill) must be verified against NEC Article 310 or IEC 60364 tables.

Frequently Asked Questions

How do I choose between 3% and 5% voltage drop?

3% is standard for branch circuits powering sensitive electronics, appliances, and lighting. 5% is the standard total maximum for the entire run from utility entrance to final load.

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Educational & Reference Notice: This calculator provides technical estimates based on standard physical formulas. Actual electrical installation, protective device sizing, and conductor selection must be verified against the applicable electrical code (NEC, IEC, CEC) by a licensed electrician or qualified professional engineer.