What is the easiest way to calculate the number of tiles for a region?

Question

OpenStreetMap

The task is to count the number of tiles covering a certain region of the map (generally speaking, not necessarily rectangular, but a rectangle is also suitable for a first approximation) at a given zoom.
I can fully imagine the mathematical side of the issue - it's not too difficult, but very dreary and time-consuming.
Is there any ready service for this? Ideally, he circled the area with a broken line, and it showed the number.

Answer 1

Tile Calculator - tools.geofabrik.de/calc