Crop Factor and Equivalent Focal Length Calculator

1. Choose your camera sensor from the list.
2. Enter your lens focal length in millimetres.
3. Add the aperture if you want the equivalent aperture too.
4. Read the crop factor and the full-frame equivalent focal length.

Crop factor is the ratio of a full-frame sensor diagonal to your sensor diagonal. A smaller sensor captures a narrower slice of what a lens projects, so the image looks cropped in, or zoomed, compared with full frame.

Multiplying your lens focal length by the crop factor gives the equivalent focal length: the full-frame lens that would frame the same scene. It lets photographers compare lenses and cameras across different sensor sizes on a common scale. This is the reason a lens described as a 35 mm equivalent means one thing on a phone and another on a mirrorless body: the equivalence, not the number stamped on the barrel, is what tells you how the shot will actually be framed.

1. The crop factor is the full-frame diagonal, about 43.3 mm, over the sensor diagonal.
2. Multiply the lens focal length by the crop factor for the equivalent focal length.
3. Multiply the aperture by the crop factor for the depth-of-field equivalent aperture.
4. The actual exposure aperture does not change; only the depth of field equivalence does.

Common crop factors are 1.5 or 1.6 for APS-C, 2 for Micro Four Thirds and around 2.7 for a 1 inch sensor.

You put a 50 mm f/1.8 lens on an APS-C camera with a 1.5 crop factor. The equivalent focal length is 50 times 1.5, which is 75 mm, so it frames like a short portrait lens on full frame. The depth-of-field equivalent aperture is f/1.8 times 1.5, about f/2.7, so it blurs backgrounds like an f/2.7 lens would on full frame, even though it still gathers light like f/1.8 for exposure. This split between framing, depth of field and exposure is the part that trips up newcomers, and running the numbers once usually makes the whole relationship click into place.

Sensor Size

The smaller the sensor, the larger the crop factor and the more a lens appears to zoom in.

Lens Focal Length

The equivalent scales directly, so a longer lens on a crop body reaches even further.

Aperture

Crop factor changes the depth-of-field equivalent aperture, but not the exposure aperture.

Format Standard

Equivalence is always relative to full frame, the common reference for comparing systems.

Equivalent focal length of a 50 mm lens by sensor.

The smaller the sensor, the more reach a given lens has, which is why crop bodies suit wildlife and sports.

Choosing a Lens

See how a lens will frame on your crop body compared with full frame.

Switching Systems

Compare focal lengths fairly when moving between sensor sizes.

Understanding Reach

Work out the effective reach of a telephoto on a crop sensor.

1. Changing the Exposure Aperture

Crop factor affects depth-of-field equivalence, not the exposure; f/1.8 still meters as f/1.8.

2. Forgetting the Lens Is Unchanged

The lens is still a 50 mm; only the framing changes on a smaller sensor.

3. Mixing Up Crop Factors

Canon APS-C is 1.6, Nikon and Sony 1.5; use the right one for your body.

4. Applying It to Full Frame

Full frame has a crop factor of 1, so no conversion is needed.

The equivalence is exact for the crop factor you choose, based on the full-frame diagonal. It compares framing and depth of field, not exposure.

It is the ratio of the full-frame sensor diagonal to your sensor diagonal. APS-C is about 1.5, Micro Four Thirds 2, and it tells you how much a sensor crops in.

Multiply the lens focal length by the crop factor. A 50 mm lens on a 1.5 crop APS-C body acts like a 75 mm lens on full frame.

It changes the depth-of-field equivalent aperture, but not the exposure. An f/1.8 lens still meters and gathers light as f/1.8.

About 1.5 for Nikon and Sony, and 1.6 for Canon. Micro Four Thirds is 2, and a 1 inch sensor is around 2.7.

Their smaller sensor captures a narrower part of the image the lens projects, cropping into the centre and appearing to magnify.

No. It is always a 50 mm lens, but it frames like a longer lens on a smaller sensor, so the view differs.

It compares depth of field across formats. An f/1.8 on APS-C blurs backgrounds like about f/2.7 on full frame, though it exposes as f/1.8.

No. Full frame has a crop factor of 1, so the focal length is already the equivalent.

No. The calculator runs entirely in your browser and nothing you enter is stored or sent anywhere.

• Crop factor (Wikipedia).
• Image sensor format (Wikipedia).
• 35 mm equivalent focal length (Wikipedia).