Circle of Confusion Calculator
The circle of confusion (CoC) is a fundamental parameter in depth-of-field calculations. It represents the largest blur spot that a viewer will still perceive as a sharp point when looking at a printed or displayed image from a standard viewing distance. The CoC depends on sensor size: larger sensors produce a larger allowable blur circle. The formula is CoC = sensor diagonal (mm) divided by a viewing-condition divisor, typically 1,730 for standard 8x10 prints viewed at 25 cm. Enter your sensor's diagonal measurement and divisor to find the CoC used in hyperfocal distance and depth-of-field calculations.
Circle of confusion formula
CoC (mm) = Sensor diagonal (mm) / Divisor
The divisor accounts for the expected enlargement and viewing distance. A divisor of 1,730 assumes the image is enlarged to roughly 8x10 inches and viewed from 25 cm. For a full-frame sensor with a 43.27 mm diagonal: CoC = 43.27 / 1730 = 0.025 mm (25 micrometers).
How CoC affects your photography
- CoC is the input used to calculate hyperfocal distance: H = (f squared) / (N x CoC), where f is focal length and N is aperture f-number.
- A larger CoC (bigger sensor) gives a larger hyperfocal distance and allows more background blur at the same aperture.
- Using a more critical (smaller) CoC divisor, such as 1,500 instead of 1,730, produces a stricter depth-of-field calculation and is appropriate for large prints or critical focus work.
- Sensor manufacturers sometimes publish their recommended CoC in their lens or camera technical documentation.
- Common full-frame CoC is 0.029 mm using divisor 1,500, or 0.025 mm using 1,730.
Circle of confusion calculator: frequently asked questions
What is the circle of confusion in photography?
The circle of confusion (CoC) is the largest blur spot that the human eye accepts as a sharp point when viewing a final print at a normal distance. It is used as the threshold in depth-of-field calculations. A smaller CoC gives a smaller (more critical) depth of field.
How is CoC calculated from sensor size?
CoC = sensor diagonal / divisor. The divisor is typically 1,730 for prints viewed at about 25 cm (10 inches) from 25 cm away, accounting for an 8x10 inch enlargement factor. Many manufacturers use 1,500 to 1,730.
Why does sensor size affect depth of field?
Larger sensors have a larger CoC threshold, which means that a larger blur circle is still considered acceptable. This results in a shallower apparent depth of field compared to a smaller sensor at the same aperture and framing.
What divisor should I use?
The most common divisor is 1,730, which assumes the image is viewed as an 8x10 print at 25 cm. Some photographers use 1,500 for a more conservative (sharper) result. Manufacturers sometimes publish their own CoC values in camera specifications.
What are typical CoC values for common sensors?
Full-frame (35mm): about 0.029 mm. APS-C (Canon): about 0.018 mm. APS-C (Nikon/Sony): about 0.020 mm. Micro Four Thirds: about 0.015 mm. Medium format 645: about 0.050 mm.
Official sources
- ISO 12232:2019: Photography, Digital still cameras, Determination of exposure index, ISO speed ratings, standard output sensitivity and recommended exposure index. Available via ISO.org.
- NIST: National Institute of Standards and Technology, reference for optical measurement standards.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.