No. Paper weight in gsm means grams per square meter, so it tells you the mass of a given area, not the thickness.

Two papers with the same gsm will only have the same thickness if they also have the same density. In practice, different paper types, coatings, and manufacturing methods change density, so thickness can vary.

That means 300gsm cardstock and 300gsm photo paper are not necessarily equally thick. Photo paper is often denser because of its coatings and construction, so a 300gsm photo paper can be thinner than a 300gsm cardstock.

So:

• same gsm = same mass per area
• different density/construction = potentially different thickness

If thickness matters for your printer, matting, or presentation, check the paper’s caliper/thickness specification rather than relying on gsm alone.