By Ahsan Khowaja · Updated 27 October 2026
How to use the crop factor calculator
- Choose a mode. Crop factor and the equivalent of my lens is the usual one. Lens I need works backwards from a full-frame focal length you know. Megapixels left is for cropping a photo after you've taken it.
- Pick your sensor size. The presets use the crop factor the camera makers quote, such as 1.5× or 1.6×. Choose Custom to type an exact width and height from your camera's spec sheet.
- Enter the focal length and aperture printed on the lens.
The result shows the crop factor, the exact figure from the sensor's measurements, the equivalent focal length and aperture, and how big the sensor is compared with full frame. It works as a crop factor calculator for lens shopping too. Type the lens you are considering and see what it will look like on your body.
What the crop factor is and how it is calculated
A sensor crop factor compares a sensor's size with the 36 × 24 mm full-frame (35 mm film) format. It is the ratio of the two diagonals:
Crop factor = 43.27 mm ÷ sensor diagonal
- 43.27 mm is the diagonal of a full-frame sensor: √(36² + 24²).
- Sensor diagonal = √(width² + height²), in millimetres.
For an APS-C sensor of about 23.5 × 15.6 mm, the diagonal is √(552.25 + 243.36) = 28.21 mm, so the crop factor is 43.27 ÷ 28.21 = 1.53. Makers round that to 1.5×. Canon's slightly smaller APS-C (about 22.3 × 14.9 mm) works out at 1.61, quoted as 1.6×. Micro Four Thirds (about 17.3 × 13 mm) is 43.27 ÷ 21.64 = 2.0.
Sensor sizes are nominal and differ by a few tenths of a millimetre between models, which is why the rounded figure is what you'll see in reviews. Wikipedia's crop factor article covers the definition in more detail.
Crop sensor focal length equivalent
Multiply the focal length by the crop factor to get the full-frame lens that gives the same view:
Equivalent focal length = focal length × crop factor
- A 50 mm lens on a 1.5× APS-C camera frames like 75 mm on full frame.
- A 24 mm lens on Canon APS-C (1.6×) frames like 38.4 mm.
- A 25 mm Micro Four Thirds lens (2×) frames like 50 mm.
- The 4.3 mm lens on a compact with a 1/2.3-inch sensor (about 6.17 × 4.55 mm, crop factor 5.64) frames like 24.3 mm. That is why a compact's box says "24 mm" when the lens is marked 4.3 mm.
The lens itself doesn't change. A 50 mm lens is still 50 mm, with the same perspective from the same spot. The smaller sensor records only the middle of the image the lens projects, so the picture looks as if it were taken with a longer lens.
To go the other way, divide. To match a 35 mm full-frame view on 1.5× APS-C, you need 35 ÷ 1.5 = 23.3 mm, so look at 23 mm or 24 mm lenses. On Micro Four Thirds, a full-frame 50 mm look needs 50 ÷ 2 = 25 mm.
Equivalent aperture: depth of field and light
The crop factor applies to the f-number as well, but only for depth of field and total light, not for exposure.
- Exposure: f/1.8 is f/1.8 on any sensor. The shutter speed and ISO you need for a correct exposure don't change.
- Depth of field: for the same framing from the same spot, multiply the f-number by the crop factor. A 50 mm f/1.8 on 1.5× APS-C has about the depth of field and background blur of a 75 mm f/2.7 on full frame. A 25 mm f/1.4 on Micro Four Thirds matches a 50 mm f/2.8.
- Total light: a 1.5× APS-C sensor has about 42% of full frame's area, so at the same settings it gathers about 1.2 stops less light in total. That is the main reason smaller sensors look noisier at the same ISO when the photos are viewed at the same size.
To match a full-frame 35 mm f/2.8 look on APS-C, you'd need about 23.3 mm at f/1.9. The depth of field calculator shows the exact sharp zone for any lens, aperture and distance.
Crop factor chart for common sensors
Approximate sensor sizes, their diagonals, crop factors and what a 50 mm lens frames like on each:
| Sensor | Size (about) | Diagonal | Exact crop factor | Usually quoted | 50 mm frames like | Area vs full frame |
|---|---|---|---|---|---|---|
| Medium format 44 × 33 | 44 × 33 mm | 55.00 mm | 0.79 | — | 39.3 mm | 168% |
| Full frame | 36 × 24 mm | 43.27 mm | 1.00 | 1× | 50 mm | 100% |
| APS-H (Canon) | 27.9 × 18.6 mm | 33.53 mm | 1.29 | 1.3× | 65 mm | 60% |
| Half-frame 35 mm film | 24 × 18 mm | 30.00 mm | 1.44 | — | 72.1 mm | 50% |
| APS-C (Nikon, Sony, Fujifilm, Pentax) | 23.5 × 15.6 mm | 28.21 mm | 1.53 | 1.5× | 75 mm | 42% |
| APS-C (Canon) | 22.3 × 14.9 mm | 26.82 mm | 1.61 | 1.6× | 80 mm | 38% |
| Micro Four Thirds | 17.3 × 13 mm | 21.64 mm | 2.00 | 2× | 100 mm | 26% |
| 1-inch type | 13.2 × 8.8 mm | 15.86 mm | 2.73 | 2.7× | 135 mm | 13% |
| 2/3-inch type | 8.8 × 6.6 mm | 11.00 mm | 3.93 | — | 196.7 mm | 7% |
| 1/2.3-inch type | 6.17 × 4.55 mm | 7.67 mm | 5.64 | — | 282 mm | 3% |
The "inch" names of small sensors don't measure the sensor. A 1-inch type sensor is only about 16 mm across the diagonal. The names date from old video camera tubes, so always work from the size in millimetres.
Half frame crop factor
Half-frame film cameras expose a 24 × 18 mm frame, half of a standard 36 × 24 mm frame. The diagonal is exactly 30 mm (√(576 + 324) = √900), so the half frame crop factor is 43.27 ÷ 30 = 1.44. A 30 mm lens on a half-frame camera frames like a 43.3 mm lens on full frame, close to a standard normal lens. The frame has half the area of full frame, so it collects one stop less light in total.
Crop factor calculator for Nikon, Canon and others
Nikon calls its APS-C format DX and its full-frame format FX. DX has a crop factor of 1.5×, so a Nikon DX 35 mm lens frames like about 52.5 mm. Sony, Fujifilm and Pentax APS-C cameras are also 1.5×, Canon's APS-C cameras are 1.6×, and Olympus/OM System and Panasonic Micro Four Thirds cameras are 2×. For the exact figure for your body, choose Custom and enter the sensor width and height from the maker's specifications.
Megapixel crop calculator
Cropping a photo afterwards makes it look like it was shot with a longer lens, but it throws away pixels. The pixels left fall with the square of the extra crop:
Megapixels left = megapixels ÷ (target focal length ÷ focal length used)²
- A 45 MP photo shot at 70 mm and cropped to look like 105 mm: 105 ÷ 70 = 1.5, and 45 ÷ 1.5² = 20 MP left (44.4% of the frame).
- A 24 MP photo at 200 mm cropped to a 400 mm look: a 2× crop, so 24 ÷ 4 = 6 MP.
That is also how a camera's own "APS-C crop mode" works: a 45 MP full-frame body shooting in a 1.5× crop mode gives about 20 MP files. To see how large those pixels will print, use the print size calculator or the megapixel calculator. Our image resizer can make the crop itself.
