DC Wire Size Calculator

Created by Luis Fernando
Reviewed by Wojciech Sas, PhD candidate
Last updated: May 17, 2022

Calculating the DC wire size is vital for budgeting any electrical project, as a bigger wire size implies more expensive cables. For that reason, we've created this tool.

As an example of how to size a DC wire, we'll calculate the wire size for a 200 amp DC system using this calculator.

You can additionally look at the FAQ section for other numeric examples, like what wire size for a 12V DC you should use.

How to calculate the size of a DC wire

The formula to calculate the wire size of a DC system is:

A = (2LIϱ) / V,

where:

  • V — Voltage drop between the source and the farthest end of the wire, measured in volts;
  • I — Current running through the wire, in amps;
  • ϱ — Resistivity of the conductor material, in ohm × meters;
  • L — Length of the wire (one-way), in meters;
  • A — Cross-sectional area of the wire, in square meters; and

🙋 Important remarks:

  • The 2 coefficient before L accounts for the return path after the current passes the load.
  • V is the product of the allowable voltage drop percentage and the source voltage.
  • ϱ is not constant; it varies with the operating temperature.
  • For source voltages above 50 V, if L<16 m, this calculator assumes a distance of 16 m so that for small lengths, the wire doesn't result in excessively tiny sizes.

Example: How to size a DC wire of 200 amp

Suppose an electrical system with a 120 V source and allowable drop of 3%, a copper cable with a maximum temperature of 50°C, operating at 200 amps at DC. The **wire size is unknown, and the one-way distance (from source to load) is 50 m.

Follow these steps to know the wire size:

  1. In the DC wire size calculator, input:
    • Source voltage: 120 V;
    • Allowable drop: 3%;
    • Material: Copper;
    • Current: 200 A;
    • Distance (D): 50 m; and
    • Maximum temperature: 50°C.
  2. That's it. The wire size for your 200 amp DC system should be 104.65 mm², or AWG = 0000 (4/0)
  3. You can check your results using the formula presented in the previous section.

Other useful tools like the DC wire size calculator

As you already know how to size a DC wire, you can take a look at other calculators:

FAQ

What wire size for a 12V DC should I use?

The wire size for a 12 V DC depends mainly on the current and the wire length. Follow these steps to calculate it:

  1. Determine the electric current I (i.e., 20 A), cable length L (i.e., 5 m), conductor resistivity ϱ (typically 2.22 × 10⁻⁸ Ω⋅m for copper), and voltage drop V (typically 3% of the source voltage).
  2. Input the values in the formula:
    A = (2IϱL) / V = (2 ⋅ 20 ⋅ 2.22 × 10⁻⁸ ⋅ 50) / (0.03 ⋅ 12 V)
  3. The result should be 0.0001235 m² or 123.5 mm².

What size wire for 30 amp DC should I use?

The wire size for a 30 amp DC depends primarily on the source voltage and the wire length. Follow these steps to calculate it:

  1. Determine the source voltage (i.e., 12 V), cable length L (i.e., 50 m), conductor resistivity ϱ (typically 2.22 × 10⁻⁸ Ω⋅m for copper), and voltage drop V (typically 3% = 0.03 of the source voltage).
  2. Input the values in the following formula:
    A = (2IϱL) / V = (2 ⋅ 30 ⋅ 2.22 × 10⁻⁸ ⋅ 50) / (0.03 ⋅ 12 V)
  3. The result should be 0.00018525 m² or 185.25 mm².

Disclaimer

These results are only a guide for informational purposes. Always consult a qualified electrician before proceeding with any electrical installation.

Luis Fernando
Source voltage
V
Allowable voltage drop (V)
%
Conductor material
Copper
Current (I)
A
One-way distance (L)
ft
Maximum wire temperature
°F
For source voltages greater than 50 V, if L<16 m, this calculator assumes a distance of 16 m so that for small lengths, the wire doesn't result in excessively tiny sizes.
Recommended wire size
Wire cross-sectional area (A)
kcmil
Wire gauge
AWG
Wire diameter (d)
in
Check out 77 similar electromagnetism calculators 🧲
Acceleration of a particle in an electric fieldAC wattageBreaker size… 74 more
People also viewed…

Angular displacement

Angular displacement calculator is the one-stop tool to calculate angular displacement using three different formulas based on your requirements.

Coffee kick

A long night of studying? Or maybe you're on a deadline? The coffee kick calculator will tell you when and how much caffeine you need to stay alert after not sleeping enough 😀☕ Check out the graph below!

Steps to calories

Steps to calories calculator helps you to estimate the total amount to calories burned while walking.

Toilet paper race mass moment of inertia

The cylinder mass moment of inertia calculator is a tool that can help you find out which cylinder/cylindrical shell/ cylindrical tube will run faster in an eventually do it yourself race experiment.
Omni Calculator
Copyright by Omni Calculator sp. z o.o.
Privacy policy & cookies
main background