The circle of confusion is the largest blur spot that still looks sharp in the final image. It is usually taken as the sensor diagonal divided by 1500. A full-frame sensor has a 43.27 mm diagonal, so its CoC is about 0.029 mm; the Zeiss formula (divide by 1730) gives 0.025 mm, the figure many lens scales use.
Every depth-of-field and hyperfocal figure depends on one assumption: how big a blur spot can get before a viewer notices it. That limit is the circle of confusion, and it scales with the sensor, because a smaller sensor is enlarged more to make the same print. This calculator takes a preset format or your own sensor width and height, works out the diagonal, and divides it by the criterion you choose. It also reports the value in micrometres, the crop factor against 35 mm, and the resolution in lines per millimetre the sensor must hold to reach that limit. The result is a convention, not a physical constant: it assumes a print around 8×10 inches seen from roughly its diagonal, so pixel peeping or large gallery prints call for a smaller value.
Choose a common format, or Custom size to enter the width and height in millimetres from your camera's specifications.
d/1500 is the classic standard, d/1730 matches Zeiss tables, and d/3000 is for large prints or close inspection.
Copy the millimetre value into a depth-of-field or hyperfocal calculation; the working shows the diagonal and division.
Result Circle of confusion: 0.025
CoC in micrometres: 25
Sensor diagonal (mm): 43.27
Crop factor vs full frame: 1
Needed resolution (lines/mm): 40
The 43.27 mm diagonal divided by 1730 gives the 0.025 mm value printed on many lens depth-of-field tables.
Result Circle of confusion: 0.029
CoC in micrometres: 28.8
Sensor diagonal (mm): 43.27
Crop factor vs full frame: 1
Needed resolution (lines/mm): 34.7
The classic criterion assumes an 8×10 inch print viewed from about 25 cm by someone with normal eyesight.
Result Circle of confusion: 0.014
CoC in micrometres: 14.4
Sensor diagonal (mm): 21.64
Crop factor vs full frame: 2
Needed resolution (lines/mm): 69.3
A 17.3 x 13 mm sensor has half the full-frame diagonal, so its acceptable blur spot is half as large.
CoC = √(w² + h²) ÷ k
w, hkCoCThe eye resolves about 0.2 mm at 25 cm. An 8×10 inch print made from a full-frame frame is enlarged about 7 to 8 times, so a spot of roughly 0.2 ÷ 7 ≈ 0.029 mm on the sensor looks like a point. Scaling by the diagonal keeps the same print size and viewing distance for every format. Crop factor is 43.27 mm divided by the diagonal, and the needed resolution is 1 ÷ CoC in line pairs per millimetre.
It is the 43.27 mm diagonal divided by about 1440 to 1500, rounded. Older tables used 0.033 mm, Zeiss used 0.025 mm. All are conventions for an 8×10 inch print viewed at normal distance, not a hard optical limit.
Only if you look at the image at a larger size. The CoC depends on final print size and viewing distance. A 45 MP file printed at 8×10 inches has the same acceptable blur as a 12 MP file; pixel peeping at 100% is a different, stricter standard.
Divide the full-frame value by the crop factor. A Micro Four Thirds sensor has a crop factor of about 2, so its CoC is around 0.014 mm instead of 0.029 mm, because it is enlarged twice as much for the same print.
It is 1 divided by the CoC: the resolution the sensor and lens must deliver for detail at the blur limit to be recorded. For full frame at d/1500 it is about 35 lines/mm, well within modern lenses.
Most 35 mm lens scales use roughly 0.025 to 0.033 mm. Zeiss documents d/1730. If your prints look softer than the scale suggests, choose d/3000 or stop down one or two stops beyond the marked value.
The manufacturer's specification sheet lists the effective sensor size in millimetres. Enter those under Custom size; nominal names like 1/2.3-inch do not equal any physical dimension on the chip.
Using this tool in an assignment, article or report? Copy a citation, or a link for your website.
Tools Directory Editorial Team. (2026, October 9). Circle of Confusion. Tools Directory. Retrieved October 27, 2026, from https://tools.milunir.com/photography/photography-planning/circle-of-confusion/
Tools Directory Editorial Team. “Circle of Confusion.” Tools Directory, 9 Oct. 2026, https://tools.milunir.com/photography/photography-planning/circle-of-confusion/. Accessed 27 Oct. 2026.
Tools Directory Editorial Team. “Circle of Confusion.” Tools Directory. Last modified October 9, 2026. Accessed October 27, 2026. https://tools.milunir.com/photography/photography-planning/circle-of-confusion/.
<a href="https://tools.milunir.com/photography/photography-planning/circle-of-confusion/">Circle of Confusion – Tools Directory</a>