Confused Awning Sizes - Please Help!!

Wonder if anyone can help

I am contemplating buying an awning this year and need a little help on sizing etc.

I understand the need to measure the rail etc and have my caravans spec book but left slightly confused by the different manufacturers size guides etc

Are all size 14 awnings the same cm length for example across all manufacturers?

For example I am trying to determine the confirmed length of a size 15 Kampa Carnival awning ( it has a 15 tab sown in fabric) - searching the net it seems to range from 1000cm to 1073 dependant on where i look 

Any help appreciated