Crop Factor Calculator
Crop factor, full-frame equivalent focal length, and sensor dimensions.
What it does
Crop factor compares the diagonal of a camera sensor with the diagonal of a 36 x 24 mm full-frame sensor. The full-frame diagonal is about 43.27 mm. A smaller sensor has a shorter diagonal, so the ratio is greater than one. A larger sensor has a longer diagonal, so the ratio is less than one.
The number is useful because photographers are used to full-frame focal lengths. A 50 mm lens on a Canon APS-C body has the same field of view as an 80.7 mm lens on a full-frame body, so the crop factor is about 1.61. The lens itself is still 50 mm. The smaller sensor simply uses a narrower part of the image circle, which looks like a crop and a magnification of the central area.
Sensor dimensions vary within the same label. Canon APS-C is about 22.3 x 14.9 mm, while Nikon, Sony, and Fujifilm APS-C sensors are closer to 23.6 x 15.7 mm. Micro Four Thirds is about 17.3 x 13 mm. A 1-inch sensor is about 13.2 x 8.8 mm. Medium format is not one size either, so the preset here is a common 43.8 x 32.9 mm sensor.
The default example is a 50 mm lens on a Canon APS-C sensor. The sensor diagonal is 26.8 mm, the crop factor is 1.61, and the equivalent focal length is 80.7 mm. The sensor area is 332.3 square millimeters. A full-frame sensor of the same 3:2 shape has a 43.3 mm diagonal and a 1.00x crop factor.
Crop factor is often used as a shortcut for reach, but it is not a free teleconverter. The smaller sensor collects less total light at the same aperture, and the depth of field at the same f-number is deeper. To compare depth of field, multiply the f-number by the crop factor as well. A 50 mm f/1.8 lens on Canon APS-C gives a field of view like 80 mm on full frame, and a depth of field closer to an 80 mm f/2.9 lens.
How to use
- Pick a sensor preset, or choose custom and enter the active width and height in millimeters.
- Enter the focal length printed on the lens. Do not enter a 35 mm equivalent value.
- Read the crop factor and the full-frame equivalent focal length.
- Use the diagonal and area to compare sensor sizes, not just the width.
- For depth of field comparisons, multiply the f-number by the crop factor.
- For video, check whether the camera applies an additional crop at the chosen resolution and frame rate.
Formula
- width
- Active sensor width in millimeters.
- height
- Active sensor height in millimeters.
- diagonal
- Diagonal of the active sensor area in millimeters.
- crop factor
- Full-frame diagonal divided by the sensor diagonal.
- focal length
- Actual focal length printed on the lens.
- equivalent
- Full-frame focal length that gives the same field of view.
The reference diagonal is 43.2666 mm, which comes from sqrt(36^2 + 24^2). Some tables use 43.3 mm, which changes the result only in the second decimal. Crop factor is a diagonal ratio, so it is exact for field of view only when the aspect ratios are the same. Comparing a 4:3 sensor with a 3:2 sensor by diagonal gives a fair field-of-view ratio, but the shapes are different. The equivalent focal length is not a physical change; the lens still projects the same image circle. The equivalent aperture for depth of field is the actual f-number multiplied by the crop factor, and the equivalent ISO for the same total light is the actual ISO multiplied by the crop factor squared.
Worked example
Example: 50 mm lens on Canon APS-C
A 50 mm lens is mounted on a camera with a 22.3 x 14.9 mm Canon APS-C sensor.
- Diagonal = sqrt(22.3^2 + 14.9^2) = sqrt(497.29 + 222.01) = sqrt(719.30) = 26.82 mm.
- Crop factor = 43.2666 / 26.82 = 1.61.
- Equivalent focal length = 50 x 1.61 = 80.7 mm.
- Sensor area = 22.3 x 14.9 = 332.3 square millimeters.
- The same 50 mm lens on a full-frame sensor has a 1.00x crop factor and an equivalent focal length of 50 mm.
- For depth of field, an f/1.8 setting on the APS-C body compares roughly with f/2.9 on full frame.
Reference table
| Format | Dimensions | Diagonal | Crop | 50 mm equivalent |
|---|---|---|---|---|
| Full frame | 36 x 24 mm | 43.3 mm | 1.00x | 50.0 mm |
| Canon APS-C | 22.3 x 14.9 mm | 26.8 mm | 1.61x | 80.7 mm |
| Nikon APS-C | 23.6 x 15.7 mm | 28.3 mm | 1.53x | 76.3 mm |
| Micro Four Thirds | 17.3 x 13 mm | 21.6 mm | 2.00x | 100.0 mm |
| 1-inch | 13.2 x 8.8 mm | 15.9 mm | 2.73x | 136.4 mm |
| Medium format | 43.8 x 32.9 mm | 54.8 mm | 0.79x | 39.5 mm |
Limits
- Presets use common active sensor dimensions. Actual cameras can differ by a few tenths of a millimeter.
- Assumes the full sensor is used. Video modes and some photo modes apply an additional crop.
- Does not calculate exposure, noise, or dynamic range differences between sensors.
- Depth of field equivalence also needs an aperture conversion and a comparison CoC, which this page does not do.
Common mistakes
- Using 1.5x for Canon APS-C when the sensor is closer to 1.6x.
- Comparing sensor width only and ignoring the aspect ratio.
- Thinking the focal length or the aperture physically changes when the sensor changes.
- Using a 35 mm equivalent focal length as the input and multiplying it again.
- Forgetting the extra crop in 4K video or in a high-frame-rate mode.
- Assuming a speed booster and a teleconverter have no effect on the crop factor.
Try it yourself
Quick checks. Answers sit tucked under each question.
What is the equivalent focal length of a 50 mm lens on Micro Four Thirds?
The crop factor is 2.00x, so the equivalent is 100 mm.
What is the equivalent focal length of a 24 mm lens on Nikon APS-C?
The crop factor is 1.53x, so the equivalent is 36.6 mm.
A custom sensor is 36 x 24 mm. What is its crop factor?
The diagonal is 43.3 mm, so the crop factor is 1.00x. A 50 mm lens stays 50 mm equivalent.
Questions
What is crop factor?
It is the ratio of the full-frame diagonal to the sensor diagonal. It tells you how much narrower the field of view is compared with a 36 x 24 mm sensor.
Does crop factor change the aperture?
The f-number stays the same for exposure, but the depth of field at that f-number changes. For an equivalent depth of field, multiply the f-number by the crop factor.
Is a 50 mm lens on APS-C the same as an 80 mm lens?
It frames like an 80 mm lens on full frame, but the lens is still 50 mm. Perspective, distortion, and the physical lens do not change.
Why is Canon APS-C 1.6x and Nikon APS-C 1.5x?
Canon APS-C sensors are slightly smaller, about 22.3 x 14.9 mm, while Nikon APS-C is about 23.6 x 15.7 mm. The diagonal ratio produces the difference.
Does crop factor affect image quality?
It affects how much of the lens image circle is used and how much total light is collected. The visible effect depends on the sensor technology, pixel size, and how the images are compared.
Why does my video look more cropped than my photos?
Many cameras apply an additional crop in 4K, high-frame-rate, or electronic stabilization modes. Check the camera's video crop factor for the exact setting.