You should be able to calculate it.
(number of glass layers x surface area x mass of dry glass per sq ft) + total mass of resin after establishing the volume.

Fibreglass  (in the U.K.)  is generally used as  1.5 ounces per squ foot for one single layer. Hence you calculate weight as a product of total area multiplied by number of thicknesses.  Sometimes we use 1 oz per squ ft;   sometimes 2.0 oz / sq ft. modify calcs as necessary to get weight of glass.   For a soggy hand lay up job assume weight of resin to be   three time as heavy. hence you get total job weight.

To get the nominal weight of a prepreg, divide the areal weight of the dry fibers by the factor (1 minus prepreg resin %). The resin content is a weight fraction of the prepreg weight. To convert the areal weight units g/m^2 to lb/ft^2 multiply by 0.000205, to convert g/m^2 to oz/yd^2 multiply by 0.0295.
Example: BMS 8-212, Ty1, Gr 95 (Graphite Uni-tape 42%)

95/(1-0.42) = 163 g/m^2

From the Boeing Composites Guide D6-46632 (93)

I recommend you correlate your theoretical values... Even the cloth manufacturers give you a range of weight for their cloths, I've seen deltas that are not trivial!

If you use vacum bagging, your resin content in the composite should be lower than with hand layups, the weight of the final product should also be lower...

A simple way to correlate your values, is to make a few test layups of 1 ft^2 pieces using the same technique as will be used during production. Weigh the dry materials (minus epoxy) before layup, then start with 1 ply, cure, measure, add another ply, cure, measure, ..., derive your weight/ply/ft^2 from all the numbers you obtain.

Site below recommends 1:1 ratio for fiberglass to resin weight. See pages 23 and 24.


 www.fiberlay.com/howto/ Fiberglass-Epoxy-Basics-Training-Guide.pdf


 


 





       

From  http://www.eagerplastics.com/glass.htm

See original website for a better printout.

Fiberglass Fabrics
         
For *1.5oz (per sq ft) mat - 20 sq ft layup per gal resin
For *6oz (per sq yd) cloth - 50 sq ft layup per gal resin
For *10oz (per sq yd)cloth - 75 sq ft layup per gal resin
For *24 oz (per sq yd)     - 20 sq ft layup per gal resin
*

The resin probably has a specific gravity ~ 1.0 so the weight of resin per ft^2 can be calculated.