Let’s say I have a guitar that the factory has set strings with the following gauge
Gauge first string 0.72mm
2 string 0.83mm
3 string 1.03mm
4 string 0.742mm
5 string 0.912mm
6 string 1.125mm
Now I want to buy another string from another brand . How do I find strings with the same or similar gauge?
Hi Tom,
The gauges should be indicated on the packaging. If you order from an online store (e.g. this one), you usually have the option to filter according to brand and gauge and other characteristics.
Is it an acoustic guitar or electric guitar?
Usually, a factory electric is set up with "9 gauge " strings. they might just be called “light gauge” as well but the string diameters will be shown on the guitar string packaging
And an acoustic will come with “12 gauge” (also “light”)
The gauge is measured after the thickness of the thinnest , high E string .
You can get a single string from some places if you need to , you can ask in the shop or just have a look at the thickness of the strings you need and see if that one is available to buy. It probably doesn’t matter if you slightly mismatch if you’re just needing a new string in a pinch
Usually , when a string breaks for me I’ll change them all. But I rarely break strings but remember I did a lot as a beginner for some reason - so I used to just change the high E a lot !
Thanks . A little confusing so based on my specification what is the equivalent guitar string? The search option is a little tricky 
I use the string for yamaha classical silent guitar
Yep, string gauge is usually given in 1/1000 of an inch. The thinnest and thickest one in your set would be 0.028 and 0.044, respectively. I found via Google this pack that looks quite similar. Are you looking for classical guitar strings?
thanks Yes for yamaha silent guitar , How did you find that in google just searched all the gauges?
I prefer popular brands like Ddario etc
I just typed “guitar string 0.028” and hoped to find something. I had a hunch it was for classical guitars as it’s thicker than usual acoustic or electric sets.
I like D’Addario’s website as they have images of the back of the packages as well, and that’s where most of the info can be found. This one might be what you’re looking for. Of course, classical strings are somewhat unique in that they are grouped by “tension” rather than the actual thickness of the strings.
OH thanks a lot , Now I understand I was confused about mm and inches
so I had no idea how did you come up with 0.028 LOL ok thanks
OH let me see I searched I came up with this
In that page there is specification is this the equivalent of what I am looking for?
Thee are a lot of places you can buy single classical strings, treble sets, bass sets and full sets. Strings by mail is a good one.
I am not a fan of the Pro Arte classical strings myself. The G tends to be a bit thumpy.
That is also a very, very high tension set of classical strings, higher than most I have seen. You may like that, but I didn’t.
Those are around 100 lbs total. My classical comes with 93 lbs and I prefer less, but am still trying them out.
The Pro Arte normal tension are closer to 85 lbs.
Personally, I think there are many better strings out there for the money.
Right now my Kremona 90th Anniversary Classical has Hannabach 815 MT (medium tension) which come in about 92 lbs. they are much better than the Pro Arte (my opinion) and about the same price. Both are on the expensive side, so look around.
My beater, an old, repaired Alvarez by Yiari CY140 has Pro Arte normal tension strings. I don’t enjoy them much, but I am too cheap just to take them off door the sack if it on a guitar I only play occasionally.
Here is my list of classical strings I want to try. Only the ones with actual comments have actually been tried.
I have in house the Curt Mangan and Savarez Cristal Corum, so those will be next, but months away at this point.
Savarez Corum Alliance 500AR ~ 85.75lb
Knobloch
300ADC ~ 85 lb
Aquila
Amber 2000
144C Light ~ 88.5 lb
Alabastro
NT 19C ~92 lb
LT 97C ~90.5 lb
Hannabach
815 MT ~92lb
Savarez New Cristal Corum
500CJ HT ~88.6lb
500CR NT ~83lb
Curtis Mangan NT ~84.95 lb
Pro Arte NT
~ 85 lbs. Thudding G string. Otherwise ok but not inspiring.
These are what I use, they’re really nice sounding (to me) and a good compromise on weight.
I have only heard good things about La Bella strings.
There are so many different strings out there it is mind boggling. All we can do is choose some and try them.
And this is why the “Système International” was created but certain countries tend to pretend it doesn’t exist and use their “imperial” (in 2022) units… Or even worse whatever stupid mix of units they want to come up with (e.g. kW/in2) 
Ok, sorry for the rant!!
Google is your friend though. You can just type something like 97666839386 mm to inches and it will do the conversion for you. Then you can search for the specific gauge or you can browse various sets of strings and check the available gauges.
Best thing to do is not to complicate things. I’ve been playing guitar for 40 years, and haven’t a clue about guitar string thicknesses. When I needed new strings recently, I phoned up my local guitar shop (Guitarguitar in Epsom), and asked them.
If you don’t know what youre doing, Google will confuse you. Phone up your local guitar shop.