You should be able to find a wire-stripping tool at any local hardware store.

Rather than providing a one-size-fits-all wire-gauging hole, many pairs of wire strippers are themselves gauged. A gauged stripper will have about 10 holes of varying gauge sizes running up and down the interior of the tool’s ‘blades. ’[3] X Expert Source Ricardo MitchellElectrician & Construction Professional, CN Coterie Expert Interview. 6 May 2020. This means that you’ll need to approximate the gauge of the wire (even if you don’t know it beforehand) to remove the insulation from the wire.

At this point, you should have 2 inches (5 cm) of exposed wiring, of which you can measure the gauge.

Although gauge sizes are universal, different companies put different amounts of plastic insulation around their wires. The diameter measurement will not be an actual gauge size, since only uninsulated solid wires are gauged.

Make sure that the gauge tool specifies which measurement system it corresponds with. If you’re located in North America, your tool will probably measure on the AWG scale. You can purchase a wire gauging tool at your local hardware store or home-supply store).

Note that each of the grooves will have a slightly larger hole located next to it. These holes are not used to measure gauge size. They’re simply on the tool to allow you to easily remove the wire from the grooves.

If you don’t have any other wires whose gauge you know, take your wire strand to a local hardware store. They’ll likely have enough gauged wire in their inventory that they can pull out various sizes of wire for you to compare your strand with.

If the wire is of a very large gauge (very small diameter) and can’t be measure with a ruler, use a wire and conduit measuring device. This tool can also be purchased at any hardware store.

This calculation will give you the Circular Mils (CMA) value for the stranded wire. CMA is another commonly used wire-gauge scale which calculates the circular area of wires. As a general rule, larger-gauge wire (smaller diameter) contains fewer strands. Large-gauge wires may contain as few as 7 or 8 strands, while small-gauge (large diameter) wires may contain as many as 20, 40, or even 100 strands.

For example, if you measure the diameter of a wire strand as 0. 005 inches (0. 127 mm) and the stranded wire has 21 strands, this corresponds to a CMA of 525 and to an AWG of 22.