Measure the length of the beetle on your screen and divide by the distance between the left sides of the two millimeter marks on your screen. I got 0.675 bar. What did you get?

I actually measured several images in this fashion and think the beetle is close to, but just under, 0.75mm.

Question: Is this a species that habituates shelf fungi? It's tiny enough to go hunting down the larval tunnels of just about any other species.