What circle of confusion value should I use for my sensor?
Use your sensor's real diagonal divided by 1500 (this site's stated convention): full frame 0.0288mm, APS-C 0.0179mm (Canon) or 0.0188mm (Nikon/Sony/Fujifilm), Micro Four Thirds 0.0144mm, and 1-inch-type 0.0106mm — each derived from that format's actual physical dimensions, not a rounded rule of thumb.
Why the Exact Figure Matters More Than It Seems
Circle of confusion sits directly in the denominator of the hyperfocal-distance formula, so a small difference in this number produces a proportional difference in every depth-of-field and hyperfocal figure computed from it. Using a generic '0.03mm for full frame'-style rounded value instead of the real 0.0288mm introduces a small but real error into every subsequent calculation, one that compounds if you're comparing across sensor formats where the relative differences matter more than any single absolute number.
Why Different Sources Give Different Values for the Same Sensor
The dividing convention itself varies — 1500, 1442 and 1730 are all genuinely used, each producing a slightly different circle of confusion (and downstream hyperfocal distance) from the identical sensor diagonal. This site states its convention explicitly (1500) specifically so its numbers can be compared honestly against another source's, rather than assuming a discrepancy means one of the two is simply wrong.
Every sensor format's exact figure, computed the same way, is listed on the sensor format reference, and used automatically once you select your sensor in the DoF & Hyperfocal Calculator.
Frequently Asked Questions
Why does Canon's APS-C sensor use a different circle-of-confusion value than Nikon's or Sony's?
Because Canon's APS-C sensor is physically slightly smaller (22.3x14.9mm against 23.5x15.6mm), giving it a smaller diagonal and therefore a smaller, stricter circle of confusion under the identical 1/1500 convention — the values differ because the sensors genuinely differ, not because of a different rule.
What circle of confusion should I use for a medium-format sensor?
The same diagonal/1500 logic applies, and since medium-format sensors are physically larger than full frame, their circle of confusion is correspondingly larger — roughly 0.0365mm for the 44x33mm format used in Fujifilm GFX and Hasselblad X bodies, computed from that sensor's real diagonal.