Copper Wire Resistance Calculator + Wire Resistance Chart (4/0 To 40 AWG)

Let’s say you want to calculate the wire resistance. Every wire conducts electricity but this conduction is not 100% effective. A bit of electricity is lost in the wire. How much exactly?

We will show you how to determine wire resistance manually and using the Wire Resistance Calculator below (just input the wire gauge and length of the wire to get the resistance in Ohms).

The resistance of any wire is dead simple to calculate if you just follow the formula. Here is the wire resistance formula we will use:

Resistance Of Wire Formula

Resistance of any wire, be it copper, aluminum, nichrome, and so on, depends only on two primary factors. The formula for the resistance of the wire includes these two factors, expressed in this electric resistance equation, also known as Ohm’s Law formula:

R = ρ × L / A

Here is how we can read this wire resistance equation: Resistance in the wire is proportional to resistivity (denoted by the Greek letter rho or ρ) and length, and reversely proportional to the cross-section of the wire (A or area). Resistance is expressed in Ohms (denoted by the Greek letter omega or Ω); 1 Ohm is equal to V/A or volt/amp.

That simply means that:

1. The higher the resistivity of the material wire is made out of, the higher the resistance in the wire.
2. The longer the wire, the higher the resistance in the wire.
3. The thicker the wire is, the lower will the resistance in the wire be.

The two primary factors we use in the wire resistance calculator (found below) are:

1. Length of the wire. This goes without saying. A 100 feet wire will have double the resistance of a 50 feet wire.
2. Resistivity of certain gauge wires (Example: 2 AWG, 10 AWG, 14 AWG, and so on). Here we combine the specific resistance of the material (ρ in the equation above) and the cross-section of the wire.

To illustrate what the resistivity of wires means, we have prepared a complete chart of the resistivity of copper wires from the thickest 0000 (4/0) AWG wire to the smallest 40 AWG wire. As you can see in this chart, the resistance of the thickest AWG copper wire is 0.04901 milliohms (mΩ) per foot and the resistance of the smallest AWG wire is 1049 milliohms (mΩ).

Note: 40 AWG wire has a 21,403 times higher resistance than 0000 (4/0) AWG wire because it has a 21,403 times lower thickness. This is the inverse relationship between resistance and cross-section or area.

Here is the full chart for resistivity of copper AWG wires that we will use in the wire resistance calculator:

AWG Copper Wire Resistance Chart

Wire Resistance Calculator

First of, pick the length of the wire. Secondly, just choose the AWG wire you are using and the calculator will automatically calculate how much resistance is in that wire:

As an example, let’s look at a 100 feet long 14 AWG wire. If you slide the first slider to ‘100’ and choose the ’14 AWG’ wire, the resistance calculator will tell you that such a wire has a total resistance of 0.25250 Ohms (Ω).

You can choose any AWG wire and do this calculation. Here is how you can manually get the same result:

How To Calculate The Resistance Of The Wire?

We will be using the formula for the resistivity of the wire above. Let’s say we have a 150 feet long 10 AWG copper wire. How much resistance is in this 10 AWG wire?

R = ρ × L / A

In this equation we know that the length (L) is 150 feet. ρ and A (or ρ/A) can be read from the AWG resistivity chart; it’s 0.9989 milliohms (mΩ) per foot or 0.0009989 ohms (Ω) per foot. We simply put both things in the wire resistance equation like this:

R (150 ft 10 AWG wire) = 0.0009989 ohms/ft × 150 ft = 0.14984 Ohms

If you the same calculation with the wire resistivity calculator above, you get the same result: A 150 ft 10 AWG copper wire has a resistance of 0.14984 Ohms (Ω).

Hopefully, now you know how to use the length of wire and resistance formula to calculate the resistance in any wire. If you don’t find your answer here, you can use the comment section below and we’ll try to help you out.