12 inches from the center of the drain to the back wall behind the tank.
Some toilets are 10" rough in. Also should be 18" from side wall to center of toilet if possible.
A standard toilet roughs in at 12" from the wall.
21"
24"
30 inches.
18 inches to center
It is preferable if the toilet roll holder is placed within the toilet itself. Usually it is within reach of the person using the toilet.
Standard height is 15" but you can get comfort height or ADA models which are 17" high. The standard toilet rough in dimension is 12", which means the outlet of the toilet at the floor is 12" from the unfinished wall, but they do make 10" and 14" rough in models. The width really depends on the type of toilet you get but remember International Plumbing Code requires 15" from the center of the toilet to the nearest wall. Hope that helps.
On a standard toilet in America the drain is 12 inches from the back wall to the center of the drain.
18" max from side wall to center.
There really does not... it depends on the type and size of the toilet, but as a rule of thumb that size covers most toilets, and is a comfortable distance to work for most situations.
Standard is 12 inches to the center of the pipe from the finished wall.
There is no standard size. But you should review your local building codes to make sure all clearances are met. Where I am from the center of the toilet must be 15 inches from the wall. This means the narrowest room allowed would be 30 inches wide. Again there must be a specific distance from the front of the bowl to the wall. This number is different depending on where you build. I wouldn't sugest the minimum unless you are tight on space. My advice would be to try out some public bathroom stalls until you find one that's just right. Then measure it.