For each product, its per-item mass (weight) and mass when on the reel is listed in the reference information on the capacitor product search product details page.
The masses are listed in this table.
Target series: GRM / GJM / GRJ / GRT / GMD / GQM / GXM / GJ4 / GJ8 series
Note that these values are typical, and the actual weight will vary slightly depending on the production lot.
Table of masses of empty reels/empty boxes (reference values)