It is printed on the lens, usually beside a ⌀ symbol on the front ring or the inside of the cap, and it belongs to that lens alone. Two lenses that mount on the same camera routinely take different sizes.
The number is cut into the front of the lens because it is a property of the lens, and no organisation publishes a list of permitted diameters.
Where to read it
On the front ring, beside a ⌀ symbol, and often on the inside of the front cap. Listings print it inconsistently: only four of the 266 products in this catalogue name a filter thread in their title, and those four carry three different diameters — 52, 58 and 67 mm. That spread across four products is the clearest evidence that the figure is per-lens.
Why it is not on the camera
Because the camera does not have one. Bodies publish a mount; lenses publish a thread. A listing that answers “what filter fits my camera” has answered the wrong question.
What the number does and does not settle
It settles that a filter of the same figure will screw in, from any maker, stacked or single. It does not settle the depth of the filter mount, which is why some are sold as slim; it does not settle whether the hood will still attach in front of it; and it does not settle what happens optically when two filters sit one behind the other.
What people ask before they commit
Can I buy one set of filters for all my lenses?
Only by buying for the largest thread and stepping down to the others with rings, and that has a cost on wide-angle lenses: a filter on a step-up ring sits further forward, the hood no longer fits, and vignetting can appear at the corners. Makers publish ring diameters; none publishes the vignetting.
Is the filter size related to the mount?
No. The mount is at the back of the lens and belongs to the camera system; the filter thread is at the front and belongs to the optical design. A lens can share a mount with a dozen others and share a thread diameter with none of them.
Last reviewed 12 September 2026