Check inches, centimeters and dimension order before buying a case
Label the physical axes, convert units once and compare internal dimensions with the object.
Product pages may list the same three dimensions in different orders. Never compare the first number in one listing with the first number in another without identifying it.
Make the check
- Write named axes. Use width, depth and thickness rather than copying an unlabeled string. Draw a small box if the product photograph makes orientation ambiguous.
- Normalize units. One inch is exactly 2.54 centimeters. Convert the whole set into one unit system and keep enough precision to notice tight clearances.
- Identify inside versus outside. A compartment measurement describes capacity; exterior dimensions describe the space the case occupies. Padding and seams explain why they differ.
- Escalate missing details. If a manufacturer gives only a screen-size label or omits an opening dimension, ask for that detail. Do not turn a rounded conversion into a fit guarantee.
A worked example
A hypothetical 30 × 22 × 2 cm device is about 11.81 × 8.66 × 0.79 inches. A compartment only 0.7 inches thick would fail the thickness check, even if its width and depth look generous. The calculation is an original example, not a compatibility statement about a named device.
What to watch out for
- Rounding a near-limit measurement can hide a failed fit.
- Manufacturing tolerances and soft shapes still matter.
- A stated maximum capacity is not a promise about a narrow zipper opening.
Write the axes before converting
Make three labeled columns: width, depth and height. Copy each source dimension into its own column before using the conversion factor. Preserve the original figure beside the converted value so you can catch a transposition later. An internal dimension should be compared with the object it holds; an exterior dimension should be compared with the surrounding compartment. Do not rearrange axes merely to make the arithmetic fit if the opening or orientation prevents that arrangement.
Sources and evidence
- Thule Koya | Thule | United States (read November 7, 2026)
- Lowepro's Workshop - Understanding bag fit | Lowepro (read November 7, 2026)
- NIST Guide to SI: inch-to-centimeter conversion (read November 7, 2026)
Use the local-only measurement and header workbench. A numerical check does not replace the source instructions or a physical fit check.
Common checks
Is a diagonal size enough for compatibility?
No. Diagonal describes a screen measurement, not the full body or a device with an added case.
Published November 7, 2026. Sources last read November 7, 2026. Send a correction.