β Circle of Confusion Calculator
Calculate the CoC for your sensor size and output conditions.
Circle of Confusion
How to Use This Calculator
Select your camera sensor, then enter the output size (in inches wide) and how far away you'll view it. The tool calculates the circle of confusion you should use when calculating depth of field for that specific sensor and print combination. A comparison table at the bottom shows how the CoC changes across all common sensor formats at the same output conditions.
Select your camera sensor from the list. If your sensor is not listed, choose the custom option and enter the width and height in millimeters.
Enter your output print width in inches. For a standard 8x10 print, enter 8. For a 20x30 gallery print, enter 20. For screen viewing, use about 8 as a baseline (equivalent to an 8-inch image at arm's length).
Set the viewing distance in inches. The standard assumption is 10 inches (about 25 cm) for a print held at comfortable reading distance. For a print mounted on a wall at 2 feet, enter 24.
Copy the CoC value into any depth of field calculator for more accurate results tailored to your actual output conditions.
Circle of Confusion Formula
The CoC is the largest blur circle on the sensor that still looks like a sharp point to a viewer of the final image. The calculation works backward from the viewer's eye resolution (about 1 arc-minute) through the print magnification to find the maximum acceptable blur size on the sensor. A smaller sensor needs a smaller CoC because it must be enlarged more to produce the same print size, making blur more visible.
Real-World Examples
When You Need This
Standard depth of field calculators use preset CoC values based on average assumptions: 0.029mm for full frame, 0.019mm for APS-C. Those values work for typical 8x10 prints, but they may not fit your situation. If you're printing 24x36 inch gallery prints and people stand close to them, or if you deliver high-resolution files to clients who zoom in on screen, the standard CoC will predict more depth of field than you actually get. Calculating a custom CoC for your output gives you accurate DOF numbers.
The opposite case is also common. If your images end up as small thumbnails on social media or as 4x6 prints, the standard CoC is actually too strict. You have more tolerance for blur than a DOF calculator implies. Knowing the real CoC for your output means you can use wider apertures and still be confident that the resulting images look perfectly sharp at their intended viewing size.
Frequently Asked Questions
What is the circle of confusion?
The circle of confusion (CoC) is the maximum acceptable blur diameter in the final image. A point of light that falls slightly out of focus forms a small disk β if that disk is smaller than the CoC, the point appears sharp to the viewer.
How is CoC calculated?
CoC = sensor_diagonal / (1730 Γ viewing_factor). The 1730 constant comes from: 1500 (viewing distance factor) Γ 1.15 (eye resolution factor). For full frame 35mm: CoC β 43.3mm / 1730 β 0.025mm.
Why does CoC depend on sensor size?
A smaller sensor must be magnified more to produce the same print size. More magnification means blur circles are also magnified more, making them more visible. Smaller sensor β smaller CoC needed.
What CoC should I use for DOF calculations?
Standard values: Full frame 0.029β0.033mm, APS-C 0.018β0.021mm, Micro Four Thirds 0.015mm. For critical work, calculate using your actual sensor size and typical print size.
Does viewing distance affect CoC?
Yes β if you view a print from farther away, larger blur circles are acceptable (smaller effective magnification). The standard assumes an 8Γ10" print viewed at 10 inches (25cm).