I am going to be using some 18/4 wire in a project, and was wondering if I connected all 4 wires together would it be the equivalent of (around) a 4.5 gauge wire?

 

I doubt it, but look up the Essex wire reference. It’ll have everything you might ever want to know about copper wire.

 

A 4.5 gauge wire? What? where how did you come to needing that size?

But in general the area of an 18 AWG wire is 1.62 kcmil and 4 x 1.62 = 6.48kcmil
A 4 AWG wire is 41.7kcmil (4 is a readily available AWG)
A 5 AWG wire is 33.1 kcmil (not readily available AWG)

6.48 is not even close to either..
You need about 25 x 18AWG wires to come close to 4 AWG.. and there are rules against paralleling wire..

 

The basic mathematical relationship of the AWG series is essentially the same as for power. Doubling the area reduces the AWG number by (approximately) 3. So doubling twice would reduce the AWG gauge by 6, taking you from 18 AWG down to 12. This same relationship means that another rule of thumb is that increasing the area by a factor of ten reduces the AWG gauge number by 10. So ten wires would take you down to about an 8 AWG and doubling that (20 wires) would get you down to 5.

 

@My Tech Guy
The easiest solution to what you're after (ie a chunky, high current wire), can be obtained from motor vehicle/automobile electrics suppliers (see for example: https://www.12voltplanet.co.uk/P008...MIh4ylg_mC2QIVhLftCh2IBgIqEAQYAiABEgLlBfD_BwE) and welding accessories suppliers (see for example: https://www.lsengineers.co.uk/weldi...MIq6S6zvqC2QIVBrvtCh2jIQ-DEAQYBCABEgLP-vD_BwE).

Such wires are far more flexible than parallelling the stiff 18 gauge wire, and come pre-insulated. The wire in the first link has a conductor area of 16 sq mm which is halfway between AWG 4.5 and 5.5. The wire in the second has a conductor area of 25 sq. mm which is halfway between AWG 2.5 & 3.5.

As you can see, they are quite economically priced as well.

 

Great information, learning a lot. Thanks!

 

I am going to be using some 18/4 wire in a project, and was wondering if I connected all 4 wires together would it be the equivalent of (around) a 4.5 gauge wire?

For these smaller sizes a general rule for two conductors is that it is that stepping up two sizes. Thus 2 #18's would equal a 14. To know exactly, use a table of wire diameters and figure that the effective cross section is proportional to the square of the diameter.