A bag can be wider than an object on paper and still be awkward to load or close. The exterior, usable compartment, opening and closure describe different constraints. Read them separately before treating a set of dimensions as a fit confirmation.
Separate the outside from the usable compartment
An external height may include a handle, while the compartment height starts inside the body. Width can refer to the base, widest point or opening. Depth may describe the exterior at its fullest point rather than a clear space available throughout the interior.
Cambridge Satchel’s size guide makes this distinction explicit. Its entry for the 13 Inch Batchel lists the following dimensions. These are the maker’s published approximate figures, not measurements made for this article.
| 13 Inch Batchel measurement | Height | Width | Depth |
|---|---|---|---|
| External, including handle | 27.5 cm | 32 cm | 7 cm |
| External, excluding handle | 22.5 cm | 32 cm | 7 cm |
| Internal | 19.5 cm | 28 cm | 5 cm |
The same bag therefore has several useful heights. The handle-inclusive figure describes its outside extent; the internal figure answers a different question. The maker also notes that handmade items can vary, so treat these numbers as approximate rather than exact clearances.
Ask how the opening changes the route inside
A compartment measurement does not describe every part of the route into it. A zip opening, folded side panel, drawstring mouth or flap can restrict the approach. Ask where the opening is measured and how far the closure is intended to open.
For a rigid item, consider the orientation in which it would pass through the opening and settle inside. Do not assume it can be rotated into position just because one diagonal appears long enough. Its thickness and corners also have to clear the surrounding structure.
The guide to linings, seams and zip guards covers details that may occupy this route. Here the fit question is whether the complete item can enter, sit and come out normally, rather than simply whether its width is smaller than the bag’s largest external width.
Compare the actual object, including its cover
For a phone, tablet or laptop, record the exact model and the dimensions of the body that will be carried. Include any sleeve, protective shell or attached accessory that stays on during packing. A screen-size label alone does not supply those three-dimensional measurements.
Bellroy’s Laptop Caddy fit guide provides a useful example: it identifies particular device models and gives dimensional limits for each caddy size. Those are the maker’s compatibility statements for that product. They should not be transferred to a different bag merely because it uses a similar size label.
The same approach works for a glasses case, notebook or watch-storage pouch. Measure the packed object rather than its contents alone, and identify which compartment it is meant to occupy.
Keep volume and closure as separate questions
Multiplying the outside height, width and depth calculates a rectangular box from those dimensions. It does not establish a bag’s usable capacity: the shape may taper, and the walls, pockets and internal structure occupy space. If a litre capacity is published, retain it as the maker’s figure unless its measurement method is known.
Closing the bag is a further check. An item may enter the compartment yet obstruct a flap, zipper or fastening. The remaining space also changes when a charger, wallet or other everyday item is added. A fit claim should name the complete arrangement that was checked.
Use a short fit-check record
| Question | What to record |
|---|---|
| Which bag and configuration? | Model, version, open or closed state, and any insert fitted |
| Which dimensions are available? | External body, usable compartment and opening; source and units |
| Which object will be carried? | Exact item plus any cover or sleeve, with its packed dimensions |
| Can it enter and sit normally? | Insertion route, orientation, visible contact and unresolved restrictions |
| Can the closure work normally? | Fastening behaviour with the intended contents, without forcing |
If you have the bag, inspect it empty first. Try the intended arrangement gently and keep the opening visible as you approach closure. Stop if an object must be compressed, the zipper forced or a panel pulled sharply out of shape. If you have only a listing, ask for the missing measurement or an interior demonstration rather than presenting an untested fit as certain.
For published reviews, use the accessory documentation worksheet to distinguish the maker’s dimensions from your own readings and any actual fit observation. This preserves the conditions needed to interpret the result.
Sources and limits
Cambridge Satchel — Size Guide, 13 Inch Batchel; Bellroy — Laptop Caddy Fit Guide. Reviewed on 15 October 2026. Manufacturer examples illustrate measurement and compatibility descriptions.
The questions above are editorial guidance. No bag-and-object combination was physically tested here. The examples do not supply missing dimensions for historical Möhel products or establish transport protection.
Explore the practical guides directory for related construction and material notes.