Drywall thickness

How thick is drywall required to be by code For interior walls? I know 1/2" is common, but is it required? This is the Midland, Mi area if that matters. Thank you in advance!

How far apart are the studs?

But, you are correct (with 16" o.c. studs,) 1/2" drywall is normal.

His question is kind of confusing.

I know 1/2" is common, but is it required?

It can be other materials as well, like Plaster, Masonry, Concrete, Paneling, etc., but drywall is common as Larry mentioned.

Also, the drywall can be 3/8" to 5/8" thick and controls the spacing of the framing holding it up, and the space it is required will determine the type and thickness required.
There are limitations to the 3/8", but can be used.

Agree with above replies.
In addition, other than ‘standard’ requirements, there are special circumstances required such as ‘fire rated’ which may have differing requirements per local AHJ.
Example: Could be 1/2" Type ‘X’… or… 5/8" standard… or… doubled 1/2" standard… etc. etc. etc.
So basically, there is no one size fits all answer.

The studs are 18" on center

I’m sorry for being vague in the original post. What I was asking is would it be acceptable by code to put 3/8" drywall on my walls. It was originally 1/2" plaster that I was planning to put the 3/8" on top of, but I think it may just be easier to strip the plaster and mount the drywall to the studs. I was just hoping that I didn’t shoot myself in the foot for already buying the drywall.