Circle of Confusion Calculator
Use this tool to estimate your camera’s acceptable circle of confusion (CoC) in millimeters and micrometers. This value is commonly used in depth of field and hyperfocal distance calculations.
What Is Circle of Confusion?
The circle of confusion is the largest blur spot that still appears acceptably sharp in the final image. Even when a point in a scene is not perfectly focused on the sensor, it can still look sharp to the viewer if that blur circle is small enough.
In practical photography, CoC is a key input for depth of field calculations. If your chosen CoC is larger, depth of field appears deeper. If you choose a stricter (smaller) CoC, depth of field becomes shallower because your sharpness standard is higher.
How This Calculator Works
Core Formula
This calculator uses a common approximation:
CoC (mm) = Sensor Diagonal (mm) ÷ Divisor
The sensor diagonal is computed from width and height using the Pythagorean theorem:
Diagonal = √(width² + height²)
With the default divisor of 1500, a full-frame sensor (43.27 mm diagonal) produces a CoC near 0.029 mm, which matches classic depth of field references.
Why Divisor Matters
- Lower divisor (e.g., 1200): larger CoC, more forgiving sharpness standard.
- Higher divisor (e.g., 1700): smaller CoC, stricter sharpness standard.
- 1500: widely used middle-ground value for general photography planning.
Typical Sensor Values (Divisor = 1500)
| Sensor Format | Approx Diagonal (mm) | Approx CoC (mm) | Approx CoC (µm) |
|---|---|---|---|
| Full Frame 36×24 | 43.27 | 0.0288 | 28.8 |
| APS-C 23.6×15.7 | 28.35 | 0.0189 | 18.9 |
| Micro Four Thirds 17.3×13.0 | 21.64 | 0.0144 | 14.4 |
| 1-inch 13.2×8.8 | 15.86 | 0.0106 | 10.6 |
When to Use a Smaller CoC
Consider using a stricter CoC (higher divisor) when:
- You are making large prints.
- Your audience views images up close.
- Your camera has high pixel density and you inspect details critically.
- You want conservative depth of field estimates for professional work.
How to Use This in Real Shooting
1) Calculate CoC for your sensor
Pick a preset or enter custom dimensions, then calculate.
2) Use CoC in DoF/Hyperfocal tools
Enter the computed CoC into your depth of field app or formula sheet for better lens planning.
3) Match output intent
If images are mostly for phone screens, a relaxed CoC can be fine. For gallery prints or technical work, use a stricter standard.
FAQ
Is there one “correct” CoC?
No. CoC depends on viewing assumptions: print size, viewing distance, and visual acuity. The calculator gives a practical estimate, not an absolute physical constant.
Why is CoC smaller on smaller sensors?
Smaller sensors usually require more enlargement to reach the same display size. To maintain equal perceived sharpness, acceptable blur on the sensor must therefore be smaller.
Does CoC depend on lens quality?
Indirectly. CoC itself is a sharpness criterion, but actual perceived sharpness also depends on lens resolution, focus accuracy, motion blur, diffraction, and post-processing.
Bottom Line
A circle of confusion value is a planning tool: it helps you translate your sharpness expectations into practical camera settings. Start with divisor 1500, then tighten or relax based on your real-world output and quality standards.