Circle of Confusion Calculator

How it is calculated

The tool uses the common diagonal rule: CoC = sensor diagonal ÷ divisor, with diagonal = √(width² + height²), all in millimetres. Preset sensor sizes are built in: full frame 36 × 24, APS-C 23.6 × 15.7, APS-H 28.7 × 19.0, Micro Four Thirds 17.3 × 13.0, 1-inch 13.2 × 8.8 and medium format 645 56 × 41.5. For a custom sensor choose the custom format and enter width and height in mm; with a preset those two fields are ignored. The divisor sets how strict the sharpness standard is. If it is empty, zero or negative, the tool uses 1500. A larger divisor gives a smaller, stricter CoC. The CoC is shown to four decimals and the diagonal to two, both in mm.

Common mistakes

• Typing the sensor's crop factor or a focal length into the width and height fields; they must be physical sensor dimensions in millimetres, and they only apply when the custom format is chosen.
• Entering width and height for a preset format and expecting them to be used; with a preset the tool takes its own built-in dimensions.
• Using the pixel dimensions of an image instead of the sensor's size in millimetres.
• Assuming a bigger divisor means a looser standard: it is the opposite, 1730 gives a smaller (stricter) CoC than 1500 for the same sensor.
• Expecting the result to depend on print size or viewing distance directly; the divisor is a stand-in for those conditions, so change it deliberately if you view very large prints or crop heavily.