If you are unable to get the model number you can measure from the center of the right arm to the center of the left arm, DO NOT take the measurements of the old fabric or roller tube.
Per the manufacturer these Awning Replacement Fabrics are folded and boxed. Each awning replacement fabric has a shelf life of 10 days starting from the day they are boxed. If the 10 day shelf life has expired it may cause wrinkling and creasing to your fabric, so please plan accordingly.
"Fabric length" is based off of the length of the whole awning (i.e. 834XX15.XXX) which will determine the "size" of the fabric needed. The actual fabric will almost always be a smaller measurement (by at least 6 inches) than the awning length.