As Loggerlee said, 1 inch per 100 yards is a very good approximation. 2 inches at 200 yards, 3 inches at 300 yards, etc.
To be ultra-precise, it is 1.0471996 inches per 100 yards.
In other fields, one minute of angle is more commonly called an arcminute. It's equal to 1/60th of a degree.