Crop Factor Calculator: Equivalent Focal Length and f-Number

How to use it

Choose your camera's Sensor from the list.
Type the Focal length (mm) of the lens and the Aperture (f-number) you use.
Read the Crop factor and the Equivalent focal length on full frame, and the Equivalent f-number on full frame.
Use the table to see the same lens on every common sensor size.

How the crop factor is defined

The Crop factor article on Wikipedia defines it as the ratio of the diagonal of a 35 mm frame, 43.3 mm, to the diagonal of the sensor in question. A full-frame sensor has a crop factor of 1. Because the 3:2 proportions of the 35 mm frame match many sensors, the ratio of heights or of widths gives the same figure for those.

The article also gives the equivalent focal length: a lens on a smaller sensor has the field of view that its focal length times the crop factor would have on full frame. The article notes that the focal length of the lens does not change; only the part of the image that is used does.

Crop factor = 43.27 mm ÷ sensor diagonal (mm)
Sensor diagonal = √(width² + height²)
Equivalent focal length = focal length × crop factor
Equivalent f-number = f-number × crop factor

Common sensor sizes and their crop factors

The table gives the width and height of common sensors from the Image sensor format article on Wikipedia, with the crop factor that article lists. The calculator computes the crop factor from each diagonal; the two agree to 0.01, and the article gives the APS-C row as 1.52 to 1.54.

Sensor	Width × height (mm)	Crop factor (article)
Full frame (35 mm)	36 × 24	1.00
APS-H (Canon)	27.9 × 18.6	1.29
Canon APS-C (EF-S)	22.3 × 14.9	1.61
APS-C (Sony, Nikon DX, Pentax, Fujifilm X, Samsung NX)	23.6 to 23.7 × 15.6	1.52 to 1.54
Four Thirds and Micro Four Thirds	17.3 × 13	2.00
1-inch	13.2 × 8.8	2.72
2/3-inch	8.8 × 6.6	3.93
1/1.7-inch	7.6 × 5.7	4.55
1/1.8-inch	7.18 × 5.32	4.84
1/2.3-inch	6.17 × 4.55	5.64
1/2.5-inch	5.76 × 4.29	6.02
1/3-inch	4.8 × 3.6	7.21

Where the equivalent f-number comes from

The Crop factor article says that the aperture has to be adjusted with the crop factor, but gives no formula. The rule used here comes from two other articles. The Depth of field article gives the approximate depth as 2 u² N c ÷ f², with u the subject distance, N the f-number, c the circle of confusion and f the focal length. The Circle of confusion article gives c as the sensor diagonal divided by 1500.

Take a crop camera with lens focal length f and f-number N, and the full-frame lens with the same framing, of focal length k × f. The circle of confusion of the crop sensor is the full-frame one divided by k, because it scales with the diagonal. The crop depth is then 2 u² N × (c ÷ k) ÷ f², which equals 2 u² (k × N) c ÷ (k × f)², the full-frame depth with an f-number of k × N. The equivalent f-number is therefore the aperture times the crop factor.

What the calculator does not cover

Image quality, noise and the number of megapixels, which depend on the sensor and the ISO and not only on its size.
Sensors that are not in the table; the table lists common sizes from the Image sensor format article.
Lenses designed for one sensor size: a lens made for a smaller sensor may not cover a full frame.

Worked example: 35 mm at f/2.8 on Canon APS-C

The Canon APS-C sensor is 22.3 × 14.9 mm, with a diagonal of √(22.3² + 14.9²) = 26.82 mm. The crop factor is 43.27 ÷ 26.82 = 1.61.

On full frame the same lens has the field of view of 35 × 1.61 = 56.5 mm, and the same depth of field as f/2.8 × 1.61 = f/4.5 at the same framing and print size.

Quantity	Value
Sensor diagonal	26.82 mm
Crop factor	1.61
Equivalent focal length on full frame	56.5 mm
Equivalent f-number on full frame	f/4.5

Frequently asked questions

What is the crop factor?

The crop factor is the ratio of the diagonal of a 35 mm full-frame image, 43.3 mm, to the diagonal of your sensor. The Crop factor article on Wikipedia defines it this way, and a full-frame sensor has a crop factor of 1.

How do I find the crop factor of my camera?

Find your sensor's width and height from the camera's manual or its specifications, work out the diagonal, and divide 43.27 mm by it. The table in this calculator lists the common sizes with their crop factors.

Does a smaller sensor change the focal length of the lens?

No. The focal length of the lens stays the same. The smaller sensor records a smaller part of the image, so the equivalent focal length is the length that gives the same field of view on full frame.

Does a smaller sensor have a deeper depth of field?

At the same f-number and the same field of view, yes. The Crop factor article says that for the same f-number, the smaller camera's depth of field is greater. The equivalent f-number above gives the full-frame aperture that matches that depth.

Is the equivalent f-number the same as the crop factor times the aperture?

Yes, for the depth of field on the same framing and print size. The Crop factor article does not state the formula; it follows from the depth-of-field approximation and the circle of confusion rule given in the Depth of field and Circle of confusion articles.

Does the equivalent f-number change the exposure?

No. The equivalent f-number describes depth of field only. The amount of light depends on the real aperture, the shutter time and the ISO, so the exposure of the lens does not change with the sensor.

Sources

Figures and text last checked on Tuesday, November 10, 2026.

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