What the standard defines
Not a standard in the sense the other pages in this section use the word. APS-C is a name borrowed from the Advanced Photo System Classic film format, discontinued as a film format, retained as a convenient label for sensors of roughly that size. Each maker publishes dimensions for its own sensors; no organisation publishes a definition that two makers can both be measured against.
What the name does reliably convey is a size class: smaller than a 36 × 24 mm frame, larger than the formats used in compact and action cameras. That class is the reason the label survives, and it is enough to tell a buyer which lenses were cut for which bodies.
What it does not promise
No single dimension. Widths vary slightly between systems, and a comparison carried out to two decimal places is a comparison of two makers’ published figures rather than of a format.
No equivalence in focal length. The millimetres engraved on a lens are the lens. An equivalent figure is that number multiplied by a ratio of sensor widths — useful for comparison, and a calculation every time. Written as though it were measured, it becomes a claim the lens never made.
No aperture change. The f-number is a ratio of focal length to entrance pupil diameter and does not change with sensor size. What changes with format, at the same f-number and framing, is depth of field — a consequence of the geometry, not a property the format publishes.
No image quality. Format is one figure among many. Nothing about noise, dynamic range or resolution follows from the size class alone, and makers publish those separately or not at all.
What it works with
Bodies and lenses cut for the format, which in this catalogue means most of the mirrorless and DSLR shelves and a good part of the lens shelves. Lenses built for the larger full-frame format generally mount and work on these bodies, using only the middle of their image circle; the reverse does not hold, and a listing that states which circle a lens covers is publishing the figure that decides it.
What people ask before they commit
Does a 24 mm lens become a 36 mm lens on APS-C?
No. The focal length engraved on the barrel is a property of the lens and does not change when the lens is mounted. What changes is how much of the image circle the sensor sees, and the equivalent figure often quoted is the engraved focal length multiplied by a ratio of sensor widths. It is arithmetic performed for comparison, and this site writes the engraved figure first and names the multiplication when it uses it.
Are all APS-C sensors the same size?
Close, and not identical. Makers publish their own dimensions, and the widths differ by a fraction of a millimetre between systems — enough to change the ratio quoted above in its second decimal place. Because no organisation publishes the format, there is no single figure to point at, and each body sheet is the source for its own sensor.
Last reviewed 12 September 2026