Commercial Industrial Supply and Harrison Plastic have a list of Schedule 40 PVS pipe fittings. The companies list the outer diameter, or O.D., and average inner diameter, or I.D., with measurements accurate to a thousandth of an inch.
All measurements are listed by their nominal size, such as 1/8 inch. Nominal pipe size is the size seen when purchasing. Listed is the minimum wall thickness allowed. They mention all manufacturers adhere to the same Schedule 40 dimensions.
They also list the maximum PSI, or pounds per square inch, the pipe can handle. Commercial Industrial Supply warns against using Schedule 40 fitting for applications requiring predominantly Schedule 80 piping, saying they have different pressure ratings.