Use the inside.
A listing may give the bag’s outside width and height. Ask for usable internal measurements if that is all you can find. Measure the narrowest part the item will occupy, not the widest outer panel.
The fit studio
Your essentials.
Their actual dimensions.
Use this flat-item check for a phone, notebook or similarly flat item. Compare measured usable internal width and height, not the outside dimensions of a bag.
A two-dimensional first check
The fit note
Ready to compare.
Enter your measurements, then choose “Compare dimensions”.
Not a packing simulation. It ignores depth, taper, rounded corners, seams, rigid dividers, zip clearance, diagonal placement and the opening. Items are checked one at a time; this does not confirm that your whole load fits together.
Get the measurements that matter.
Check the opening.
An item can be smaller than the inside compartment and still fail to pass through a zip or rigid frame. Check opening width and shape separately. The planner does not calculate this.
Test the full load.
Your phone, case, wallet and glasses need to fit together, with the bag closing normally. This tool compares one flat rectangle. A real-world packing test is still the useful final check.