What is crop factor in photography?

Crop factor (also called focal length multiplier) is the ratio of the diagonal of a full-frame 35 mm sensor (43.27 mm) to the diagonal of a smaller sensor. It tells you how much of the image circle a lens produces is actually captured. A crop factor of 1.5x means the sensor diagonal is 1.5 times smaller than full frame, so a 50 mm lens behaves like a 75 mm lens in terms of field of view. APS-C sensors typically have a crop factor of around 1.5x to 1.6x, Micro Four Thirds sensors 2x, and 1-inch sensors about 2.7x.

How do I calculate equivalent focal length?

Equivalent focal length = actual focal length x crop factor. For example, a 50 mm lens on an APS-C camera with a crop factor of 1.5 gives an equivalent focal length of 75 mm on full frame. This means the field of view matches what a 75 mm lens would produce on a full-frame camera. The physical focal length of the lens does not change; only the portion of the image circle captured by the sensor changes.

Does crop factor affect aperture and depth of field?

Crop factor does not change the physical aperture of a lens, but it does affect the equivalent depth of field when comparing systems. To get the same depth of field on a cropped sensor as on full frame, you multiply the f-number by the crop factor. For example, f/1.8 on an APS-C sensor (crop factor 1.5) gives equivalent depth of field to roughly f/2.7 on full frame. The actual light gathering (exposure) is unchanged by the crop factor; only the depth of field comparison differs between sensor sizes.

Crop Factor Calculator

This calculator works out the crop factor for any camera sensor, showing how a smaller-than-full-frame sensor changes the field of view and depth of field you get from a given lens. Enter your sensor's width and height in millimetres, or pick from presets covering full frame, APS-C, Micro Four Thirds, 1-inch and medium format, along with your lens's actual focal length and aperture. You can also switch the reference sensor away from the standard 35 mm full-frame size if you are comparing two non-standard formats. The calculator returns your crop factor, the sensor diagonal, the equivalent focal length your lens produces compared with full frame, and the equivalent aperture for matching depth of field, plus a full breakdown of the sensor and lens maths and a table showing how common focal lengths translate at your crop factor. Use it to work out what a lens will actually look like on your camera before you buy it, to compare gear across different sensor sizes, or to understand why a 50 mm lens feels tighter on a cropped sensor than on full frame. Crop factor changes field of view and depth-of-field comparisons only; it does not alter the lens's physical aperture or actual light-gathering ability. Sensor dimensions are nominal figures from manufacturer specifications, so treat the results as a close approximation rather than an exact match for every individual camera model.

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Standard Formula Based on the 35 mm full-frame diagonal of 43.27 mm (ISO 1007:1976 standard film frame).

1. Sensor Size

Sensor preset

Sensor width (mm)

Sensor height (mm)

2. Lens Specifications

Actual focal length (mm)

Actual aperture (f-number)

Reference sensor (full frame)

Crop Factor Results

Crop Factor
-
x full frame diagonal

Sensor Diagonal

Equiv. Focal Length

mm (full frame equiv.)

Equiv. Aperture

Full frame depth of field equiv.

Sensor Calculation

Sensor dimensions-

Sensor diagonal-

Reference (full frame) diagonal-

Crop factor-

Lens Equivalents

Actual focal length-

Equivalent focal length-

Actual aperture-

Equiv. depth-of-field aperture-

Common Focal Length Equivalents at This Crop Factor

Actual Focal Length	Equivalent Focal Length	Typical Use

Summary: Enter sensor dimensions above.

How Crop Factor Works

Crop factor (also called focal length multiplier) compares the diagonal of a camera sensor to the diagonal of a traditional 35 mm film frame, which measures 36 x 24 mm and has a diagonal of 43.27 mm. When a sensor is smaller than full frame, it captures only the central portion of the image circle projected by the lens, effectively cropping the image. The crop factor tells you how many times smaller the sensor diagonal is compared to the full-frame standard.

The formula is straightforward:

Sensor diagonal = sqrt(width² + height²)

Crop factor = Full frame diagonal (43.27 mm) / Sensor diagonal

Common Sensor Sizes and Crop Factors

Sensor Type	Dimensions (mm)	Diagonal (mm)	Crop Factor
Medium Format 645 (Fujifilm GFX)	43.8 x 32.9	54.77	0.79x
Full Frame (35 mm)	36 x 24	43.27	1.0x
APS-H (Canon 1D)	27.9 x 18.6	33.53	1.29x
APS-C (Nikon, Sony, Pentax)	23.5 x 15.6	28.21	1.53x
APS-C (Canon)	22.3 x 14.9	26.82	1.61x
Micro Four Thirds	17.3 x 13.0	21.64	2.00x
1-inch	13.2 x 8.8	15.86	2.73x
1/1.7-inch (compact)	7.2 x 5.4	9.00	4.81x
1/2.3-inch (smartphone-class)	6.17 x 4.55	7.67	5.64x

Equivalent Focal Length

To find the field of view equivalent on full frame, multiply your actual focal length by the crop factor:

Equivalent focal length = Actual focal length x Crop factor

For example, a 35 mm lens on an APS-C camera (crop factor 1.53) gives the same field of view as a 53 mm lens on full frame. This is why APS-C shooters often choose a 35 mm lens as their standard lens, whereas full-frame shooters typically use a 50 mm for the equivalent perspective.

Crop Factor and Depth of Field

Crop factor does not change the actual aperture of a lens (which determines light gathering and exposure). However, to achieve the same depth of field as full frame, you need to account for the crop factor in the aperture as well:

Equivalent aperture (for depth of field) = Actual aperture x Crop factor

A 25 mm f/1.4 lens on Micro Four Thirds (crop factor 2.0) is equivalent in field of view to a 50 mm lens, and in depth of field to a 50 mm f/2.8 on full frame. To match full-frame background blur with an equivalent lens, you need to open up proportionally wider on the cropped sensor.

Worked Example

A Nikon APS-C sensor measures 23.5 x 15.6 mm. Its diagonal is sqrt(23.5² + 15.6²) = sqrt(552.25 + 243.36) = sqrt(795.61) = 28.20 mm. The full-frame reference diagonal is sqrt(36² + 24²) = 43.27 mm. The crop factor is 43.27 / 28.20 = 1.53x. A 50 mm f/1.8 lens on this camera gives an equivalent focal length of 50 x 1.53 = 76.7 mm (rounded to 77 mm), and an equivalent depth-of-field aperture of f/1.8 x 1.53 = f/2.8 compared to a full-frame camera. These are the default values shown by the calculator above.

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Sources and method: Crop factor formula derived from the ISO 1007:1976 standard 35 mm film frame size (36 x 24 mm). Sensor dimensions from manufacturer specifications (Nikon, Canon, Sony, Olympus/Panasonic, Fujifilm). Diagonal calculated using the Pythagorean theorem: d = sqrt(w² + h²).

Sensor dimensions vary slightly between manufacturers and individual camera models. Crop factor figures are approximations based on nominal sensor sizes. Check your camera's official specifications for exact dimensions.