Crop Factor Calculator
Convert any sensor size to its crop factor, 35mm-equivalent focal length, equivalent aperture and angle of view.
Pick a sensor and enter a focal length — everything updates as you type.
- Crop factor
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- Equivalent focal length
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- Equivalent aperture (depth of field)
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- Sensor diagonal
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- Sensor area vs full frame
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- Light-gathering difference
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- Angle of view — horizontal
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- Angle of view — vertical
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- Angle of view — diagonal
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Crop factors by sensor format
| Format | Size (mm) | Diagonal | Crop factor |
|---|
Crop factor is measured against the 36 × 24 mm full-frame diagonal of 43.27 mm. Because sensor shapes differ (3:2 vs 4:3), the equivalent focal length matches the diagonal angle of view exactly and the horizontal/vertical framing only approximately.
How it works
The crop factor of a sensor is the ratio of the full-frame diagonal to that sensor's diagonal:
crop = √(36² + 24²) ÷ √(w² + h²) = 43.27 ÷ sensor diagonal. A Micro Four Thirds
sensor measures 17.3 × 13 mm, so its diagonal is 21.64 mm and the crop factor is 2.0. Multiply
your lens's focal length by that number to get the 35 mm equivalent focal length —
the full-frame lens that would frame the same scene. A 25 mm lens on Micro Four Thirds sees what
a 50 mm lens sees on full frame.
The same multiplier applies to the aperture when you compare depth of field and total light
gathered: 25 mm f/1.8 on Micro Four Thirds gives roughly the depth of field and the same total
light as 50 mm f/3.6 on full frame. It does not change your exposure — f/1.8 is still
f/1.8 for the light meter, so your shutter speed and ISO stay the same. The angles of view come
straight from the sensor dimensions: AoV = 2 × arctan(sensor size ÷ (2 × focal length)),
calculated separately for width, height and diagonal.
Pick a preset or type your own sensor dimensions, and the calculator also works backwards: tell it the full-frame look you want and it divides by the crop factor to give the lens you actually need. Everything runs in your browser in plain JavaScript — no uploads, no accounts, no ads.
Frequently asked questions
How is crop factor calculated?
Crop factor is the full-frame diagonal divided by your sensor's diagonal: √(36² + 24²) ÷ √(width² + height²), or 43.27 mm ÷ sensor diagonal. A Micro Four Thirds sensor is 17.3 × 13 mm, so its diagonal is 21.64 mm and its crop factor is 2.0. Canon APS-C (22.3 × 14.9 mm) works out to 1.61×, and Nikon, Sony and Fujifilm APS-C (23.5 × 15.6 mm) to 1.53×.
What is the 35mm-equivalent focal length of my lens?
Multiply the focal length printed on the lens by the crop factor. A 25 mm lens on Micro Four Thirds (2.0×) frames like a 50 mm lens on full frame; a 50 mm lens on Canon APS-C (1.61×) frames like an 80.7 mm lens. The equivalence matches the diagonal angle of view exactly — horizontal and vertical framing differ slightly when the sensor aspect ratios differ, such as 4:3 versus 3:2.
Does the crop factor change my aperture or exposure?
It changes the equivalent aperture but not the exposure. Multiply the f-number by the crop factor to compare depth of field and total light gathered: 25 mm f/1.8 on Micro Four Thirds looks like 50 mm f/3.6 on full frame. For metering, f/1.8 is still f/1.8, so your shutter speed and ISO stay exactly the same — the smaller sensor simply collects less total light, which this calculator reports as a difference in stops.