# DC Wire Size Calculator

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 also look at the FAQ section for other numeric examples, such as what wire size you should use for a 12V DC.

## How to calculate the size of a DC wire

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

**A = (2DIϱ) / 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;**D**— One-way distance (how far is the cable run from its source to the farther point), in meters;**A**— Cross-sectional area of the wire, in square meters; and

🙋 **Important remarks:**

- The
**2**coefficient before**D**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 the wire doesn't result in excessively tiny sizes for small lengths.

## 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:

- 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.

- That's it. The wire size for your 200 amp DC system should be 104.65 mm², or AWG = 0000 (4/0)
- 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:

- 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). - Input the values in the formula:

**A = (2IϱL) / V = (2 ⋅ 20 ⋅ 2.22 × 10⁻⁸ ⋅ 50) / (0.03 ⋅ 12 V)** - 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:

- 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). - Input the values in the following formula:

**A = (2IϱL) / V = (2 ⋅ 30 ⋅ 2.22 × 10⁻⁸ ⋅ 50) / (0.03 ⋅ 12 V)** - 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.