Conduit Bender Marks:

It's slightly different on each former. Get a set square, put that on the outside edge of the former, sat on the pipe and thats the outside of the bend.

Guides which show it better than a written description here:

Bender instructions

Another: Bender instructions 2

Of course the two types work slightly differently.

I also have some course handouts. However, I tip my hat to anybody who can bend a pipe to the exact dimensions first time.

Naturally, if you just need an L-shape, you can trim the ends afterwards.

For things like an S-bend, my approach has involved a degree of trial and error. So put two marks a certain distance apart which is your first estimate guess. Put the mark at the edge of the hook which holds the pipe. Make the bends. If they are correct, have a cup of tea and a biscuit. If not, adjust the distance between the marks. Repeat as necessary.

I hang my head in shame, but it does work, albeit with some waste.

Of course the two types work slightly differently.

I also have some course handouts. However, I tip my hat to anybody who can bend a pipe to the exact dimensions first time.

Naturally, if you just need an L-shape, you can trim the ends afterwards.

For things like an S-bend, my approach has involved a degree of trial and error. So put two marks a certain distance apart which is your first estimate guess. Put the mark at the edge of the hook which holds the pipe. Make the bends. If they are correct, have a cup of tea and a biscuit. If not, adjust the distance between the marks. Repeat as necessary.

I hang my head in shame, but it does work, albeit with some waste.