Very good choice for such an affordable bag, I did some "experiments" by buying 2-3 different types of cheap bags (under 5 euros) for a few A4-sized books/notebooks and this is the best one out of the ones I bought, both in terms of durability and "convenience" in putting in and taking out items.
In terms of volume, I would say it could fit A4-sized materials with a thickness that would reach two 200-250 page books.