Two bags with the same stated capacity can hold objects differently. Shape, internal dividers and the size of the opening all matter.
Check compartment measurements
A laptop’s screen diagonal does not give its full external dimensions. Compare the device, including any case, with the compartment measurements provided for the bag.
Look at the carrying setup
Consider strap length, adjustment range and handle drop. Product photos may help show the arrangement, but do not establish how it will fit your body.
Ask for missing measurements before ordering. Do not infer waterproofing, load capacity or protective performance from the appearance of the fabric.