Your caravan awning measurement or 'A' measurement will be in your hand book for your caravan.
If you don't have a hand book then the correct way to ascertain the 'A' measurement is to measure from ground to ground, along the caravan channel (as shown by the dotted line on the diagram).
How to measure your Caravan Awning The "A-A" measurement is easily done by running a length of string from the ground, around the awning channel to the ground at the other end.
You will find that this is easier to do with two people than struggling to do it alone. Lay the string out straight and then measure it in centimeters (cms). This will be the size of awning you require for your caravan. Most awning makers have sizes in ranges.
For instance, you may measure your awning as 934 cms. A maker may offer 950 which is 925-950 range. Another will offer a 960 which is 930-960 range. The size ranges may differ, but the principle is still the same.
In any case, armed up with the exact measurement of awning you require, we will be able to easily advise you on what size range to get and you are less likely to make an expensive mistake.
Please see the following link for further information
https://www.vango.co.uk/gb/blog/how-to-measure-for-a-caravan-awning.html