You would be best checking with the awning manufacturer, my guess is you would need a 975 -1000cm and there are also different size configurations from different manufacturers. Have you checked the caravan handbook for the correct size? Or you could get some thin string and measure from the ground front, around the awning rail to the ground rear to get a size, if unsure.
My caravan awning size is 903cm, I purchased a German made awning (DWT Zelt), size 12, 881 – 910cm and gives a perfect fit; they do a size 15, 971 - 1000cm.