# Wire Gauge Calculator

The **wire gauge calculator** lets you know the **diameter** and **cross-sectional** **area** of your chosen wire, as well as the **electrical** **resistance per unit length**. This is all very useful if you are wiring up speakers to your home theater system, and you were looking for a speaker wire gauge calculator.

Use this wire gauge size calculator instead of wading through those tedious wire gauge chart. It supports both the **American Wire Gauge (AWG)** standard and the **Standard Wire Gauge (SWG)** system. Read on to understand more about these ways of measuring wire sizes.

## The American Wire Gauge (AWG) standard

**American wire gauge** is a logarithmically stepped wire gauge system used mainly in North America since 1857. It applies to a solid, round, nonferrous, electrical wire. AWG is also commonly used to specify the size of **jewelry****, namely body piercing**.

For **increasing AWG numbers**, the diameter and cross-sectional area of the wire gets **smaller.** The scale is defined at two points, in terms of wire diameter. Number **36 AWG** wire has a **diameter of 0.005 inches**, while **0000 (4/0) AWG** wire has a **diameter of 0.46 inches**. The ratio of these two diameters is **1:92** and there are **40 gauge sizes** between them, giving **39 steps**. The difference in diameter of each successive gauge is a constant ratio of **92 ^{1/39}**. Between two steps of gauge number, the ratio difference is 92

^{2/39}, and so on. The formula for the diameter for any AWG number,

`n`

, is:`diameter (in) = 0.005 inch * 92`

^{(36-n)/39}

`diameter (mm) = 0.127 mm * 92`

^{(36-n)/39}

For AWG gauge numbers **00**, **000**, and **0000**, a negative number must be used for `n`

. So, for gauge 00, use `n=-1`

; 000, use `n=-2`

; and for 0000, use `n=-3`

.

As a rule of thumb, if you **decrease the AWG by six**, the diameter of the wire will **double**. Test this out in the wire gauge calculator if you like.

The **cross-sectional area** in terms of the AWG number `n`

can be found using the area of a circle:

`area = (π/4) * diameter²`

`area (in²) = 0.000019635 inch² * 92`

^{(36-n)/19.5}

`area (mm²) = 0.012668 mm² * 92`

^{(36-n)/19.5}

The resistance per unit length calculation (discussed later on) requires the cross-sectional area of the wire to be computed.

## The Standard Wire Gauge (SWG)

This wire gauge calculator also supports the **British Standard Wire Gauge (SWG)**, also known as the Imperial Wire Gauge or the British Standard Gauge. SWG is not so popular these days, but it is still used to define the thickness of **guitar strings**, as well as some types of electrical wiring.

SWG is built on the base unit of the mil, which is **0.001 inch**, or a thousandth of an inch. The gauge number defines the diameter of the wire and ranges from the largest, number **7/0 at 500 mil (0.5 inch)**, to the smallest, number **50 at 1 mil (0.001 inch)**. Each step of the scale reduces the weight per unit length by approximately **20** **percent**. The **weight per unit length** of a wire is proportional to its **cross-sectional area**, which in turn is related to the square root of the diameter:

`diameter reduction per step = (1 - √(1 - 0.2)) * 100 = 10.6%`

Unfortunately, the SWG scale doesn't follow this relationship precisely. The steps between the gauges are held constant over a range of gauges, before changing to a new constant for the next range. These changes in steps **approximately** follow an exponential curve. This system means that to learn the diameter of a particular gauge, you need to **look it up in a gauge chart** (shown below).

SWG Gauge | Diameter (in) | Diameter (mm) | Step (in) |
---|---|---|---|

7/0 | 0.5 | 12.7 | 0.036 |

6/0 | 0.464 | 11.786 | 0.032 |

5/0 | 0.432 | 10.973 | |

4/0 | 0.4 | 10.16 | 0.028 |

3/0 | 0.372 | 9.449 | 0.024 |

2/0 | 0.348 | 8.839 | |

0 | 0.324 | 8.23 | |

1 | 0.3 | 7.62 | |

2 | 0.276 | 7.01 | |

3 | 0.252 | 6.401 | 0.02 |

4 | 0.232 | 5.893 | |

5 | 0.212 | 5.385 | |

6 | 0.192 | 4.877 | 0.016 |

7 | 0.176 | 4.47 | |

8 | 0.16 | 4.064 | |

9 | 0.144 | 3.658 | |

10 | 0.128 | 3.251 | 0.012 |

11 | 0.116 | 2.946 | |

12 | 0.104 | 2.642 | |

13 | 0.092 | 2.337 | |

14 | 0.08 | 2.032 | 0.008 |

15 | 0.072 | 1.829 | |

16 | 0.064 | 1.626 | |

17 | 0.056 | 1.422 | |

18 | 0.048 | 1.219 | |

19 | 0.04 | 1.016 | 0.004 |

20 | 0.036 | 0.914 | |

21 | 0.032 | 0.813 | |

22 | 0.028 | 0.711 | |

23 | 0.024 | 0.61 | 0.002 |

24 | 0.022 | 0.559 | |

25 | 0.02 | 0.508 | |

26 | 0.018 | 0.4572 | 0.0016 |

27 | 0.0164 | 0.4166 | |

28 | 0.0148 | 0.3759 | 0.0012 |

29 | 0.0136 | 0.3454 | |

30 | 0.0124 | 0.315 | 0.0008 |

31 | 0.0116 | 0.2946 | |

32 | 0.0108 | 0.2743 | |

33 | 0.01 | 0.254 | |

34 | 0.0092 | 0.2337 | |

35 | 0.0084 | 0.2134 | |

36 | 0.0076 | 0.193 | |

37 | 0.0068 | 0.1727 | |

38 | 0.006 | 0.1524 | |

39 | 0.0052 | 0.1321 | 0.0004 |

40 | 0.0048 | 0.1219 | |

41 | 0.0044 | 0.1118 | |

42 | 0.004 | 0.1016 | |

43 | 0.0036 | 0.0914 | |

44 | 0.0032 | 0.0813 | |

45 | 0.0028 | 0.0711 | |

46 | 0.0024 | 0.061 | |

47 | 0.002 | 0.0508 | |

48 | 0.0016 | 0.0406 | |

49 | 0.0012 | 0.0305 | 0.0002 |

50 | 0.001 | 0.0254 |

## Electrical resistance per unit length

This wire gauge calculator also calculates the **electrical resistance per unit length** of wire. To calculate that, we need to know a fundamental property of the electrical conductor material that forms the core of the wire - **resistivity**. Here is its equation:

`ρ = R * (A/l)`

where:

`R`

is the electrical resistance`A`

is the cross-sectional area of the wire`l`

is the length of the wire

To find the **resistance per unit length of wire**, we can rearrange the resistivity equation in terms of `R/l`

:

`R/l = ρ/A`

So, it's merely a case of **dividing the resistivity by the cross-sectional area**. To get the total resistance of a particular wire, **multiple the above result by the length of the wire**, or use our wire resistance calculator. And if you are interested in knowing the **voltage drop** along your wire, the voltage drop calculator is just the ticket.

## How to use the wire gauge calculator?

Let's now go through step-by-step how to use the wire gauge calculator. It's quite straightforward.

- Select either the
**AWG**and**SWG**wire gauge standards. - Select the
**wire gauge number**you require. - Select the
**wire core material**. For most wires, this will be**copper**. The resistance calculation assumes that the wire is at room temperature.**Advanced mode**: If your wire core material is not listed, enter the advanced mode, and you will be able to enter a custom value for the material's**resistivity**. - Results time! The
**diameter**,**cross-sectional area**, and**electrical resistance per length**will then appear. - To
**change any of the units**of these quantities, simply click on the current unit and select a new unit from the drop-down menu.

## Worked example using the American wire gauge calculator - 12 gauge wire

To finish up, here is a worked example of how to calculate the wire diameter, cross-sectional area and electrical resistance per unit length of **12 gauge wire**. First let's calculate the **diameter** of the wire:

`diameter = 0.005 inch * 92`

^{(36-12)/39} = 0.0808081 inch

Followed by the **cross-sectional area** calculation:

`area = (π/4) * diameter² = 0.785398 * 0.08081² = 0.0051286 inch²`

If the electrical conductor material of the wire is **copper**, we would use the resistivity value for copper at room temperature, which is `1.68*10`

in metric units. Given there are 39.37 inches in a meter, that's:^{-8} Ω·m

`1.68*10`

^{-8} * 39.37 = 6.6142*10^{-7} Ω·inch

Then the resistance per unit length can be calculated:

`resistance per inch = 6.6142*10`

^{-7} / 0.0051286 = 0.00012896 Ω/inch

It is more common to state the resistance per unit length in the imperial system as **Ohms per 1,000 feet**, or **kilofeet (kft)**. Since there are 12 inches per foot, you multiple the above number by 12,000:

`resistance per kft = 0.00012895 Ω/inch * 12000 = 1.5476 Ω/kft`