DuraGRIT carbide sanding discs and sanders are exactly the US standard Mesh size for each grit grade, the same way ordinary sanding products are. 

The difference is as follows:

As soon as you start using an ordinary  sandpaper product (say an 80 grit disc or sanding block), the grit starts wearing and degrading. So at the end of a large sanding project, you will be using something akin to 120 or 150 grit and will have an uneven sanded finish, not to mention worn, torn backing paper.

DuraGRIT carbide discs and blocks, do not degrade in the same way. Grit doesn't come loose and the steel backing doesn't tear. At the end of a large sanding project, you will still be sanding in 80 grit and will have a consistent finish all over the job. To sand at a smoother grade, it is necessary to switch to a higher grit number. This is the way sanding should be and can take some time to get used to. 

Some users have indicated to us that when they discovered that their DuraDISCs lasted such a long time, they ended up mounting their two favorite grit grade discs (e.g, 80 & 150) on two Random Orbital Sanders and switch sanders, not discs.