Before choosing a bag, collect the items you use on a typical day. Include the less obvious ones: a charger, glasses case, bottle or an extra layer.
Measure the awkward items
Compare the dimensions of larger objects with the bag’s usable interior and opening. A listed overall dimension does not always describe the space inside a padded compartment.
Consider access as well as capacity
Decide which items you need to reach quickly and which can stay packed. Too many separate pockets can be as inconvenient as too few.
Check the bag’s weight, strap adjustment and intended use. A capacity number is useful, but the layout is what makes it work for your day.