Camera Crop Factor Calculator
Same Lens, Different Frame
Put an 85 mm lens on a full-frame body and it behaves like an 85 mm lens. Put it on a smaller sensor and the field of view tightens as though it were a longer lens, because the smaller sensor simply crops into the image circle the lens projects. Crop factor is the number that quantifies that difference, and it's a straightforward ratio of sensor diagonals rather than anything mysterious about the lens itself.
The Formula
Crop Factor = Full-Frame Diagonal ÷ Sensor Diagonal
Equivalent Focal Length = Focal Length × Crop Factor
Equivalent Aperture (for depth of field) = Aperture × Crop Factor
Full-frame diagonal is fixed at √(36² + 24²) ≈ 43.27 mm. The equivalent-aperture line matters because crop factor only changes the angle of view and depth-of-field character of a lens — it does not change the actual light-gathering f-number used for exposure.
Where This Calculation Matters
- Comparing gear across formats — converting a lens's real focal length into "full-frame equivalent" is the only way to compare reach and framing across camera systems fairly.
- Wildlife and sports — a longer effective reach from a cropped sensor is often treated as a practical advantage for distant subjects.
- Wide-angle and architecture work — the same crop effect is a disadvantage here, since a 16 mm lens no longer delivers as wide a field of view on a cropped body.
- Depth-of-field expectations — the equivalent-aperture figure explains why the same f-number produces visibly different background blur across formats.
Crop Factors by Common Sensor Format
| Format | Sensor size | Crop factor |
|---|---|---|
| Full Frame | 36 × 24 mm | 1.0x |
| APS-C (Nikon / Sony / Fujifilm) | 23.5 × 15.6 mm | 1.53x |
| APS-C (Canon) | 22.3 × 14.9 mm | 1.61x |
| Micro Four Thirds | 17.3 × 13.0 mm | 2.0x |
| 1-inch | 13.2 × 8.8 mm | 2.73x |
Figures are computed directly from each format's sensor dimensions using the diagonal-ratio formula above; actual sensor dimensions vary slightly between camera models within a format.
How to Use This Calculator
- Enter the sensor width in millimeters.
- Enter the sensor height in millimeters.
- Optionally enter the lens's actual focal length in millimeters to get the full-frame-equivalent focal length.
- Optionally enter the lens's aperture to get the equivalent aperture for depth-of-field comparison.
- Select Calculate to see the crop factor and any equivalents.
Related Calculations
Once you know your effective focal length, check the resulting field of view with the Camera Focal Length Calculator, or see how sensor format changes depth of field with the Depth of Field Calculator.