The tl;dr is 30 liters combined, and the source is I just measured it. The large main compartment is 24 liters, and the front zippered pocket is six liters, for a combined 30 liters. You can really stuff this pack, though, so the 35 liters listed in the description is pretty accurate. Hope this helps.
The long and exact answer follows for anyone who's curious. The dimensions: the large main compartment of the pack is 19" × 13" × 6", for a total of 1482 cubic inches. The front zippered pocket is 11" × 11" × 3", for a total of 363 cubic inches. Combined for a total of 1845 cubic inches, or converted, 30 liters total storage space for the pack.