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Focal Length
Calculator.
What does 23mm mean on APS-C? How long is your iPhone's telephoto in "real" millimetres? Convert focal lengths between full frame, APS-C, Micro Four Thirds, medium format and iPhone — with crop factor and angle of view.
Your sensor format
Crop factors & image circle at a glance
| Sensor format | Sensor (mm) | Crop factor | 50 mm equals |
|---|---|---|---|
| Full frame / 35mm | 36 × 24 | 1.0× | 50 mm |
| APS-C (Fuji / Sony / Nikon) | 23.5 × 15.6 | 1.5× | 75 mm |
| APS-C Canon | 22.3 × 14.9 | 1.6× | 80 mm |
| Micro Four Thirds | 17.3 × 13.0 | 2.0× | 100 mm |
| 1 inch | 13.2 × 8.8 | 2.7× | 135 mm |
| Medium format (GFX) | 43.8 × 32.9 | 0.79× | ≈ 40 mm |
| iPhone 15/16 Pro main | ≈ 9.8 × 7.3 | ≈ 3.5× | — |
More free calculators
What is the crop factor?
The crop factor (also format factor or focal length multiplier) describes how much smaller a sensor's field of view is than full frame — the 36 × 24 mm film format that today is called "full frame". Full frame has a diagonal of 43.3 mm. Divide that diagonal by the diagonal of another sensor and you get its crop factor.
Important: the crop factor does not change the focal length. A 35 mm lens is physically a 35 mm lens on any camera. What changes is the framing: a smaller sensor only "sees" the middle of the image circle the lens projects. The result looks zoomed in — hence "focal length multiplier".
Converting focal length: the formula
35mm equivalent = real focal length × crop factor.
- 23 mm on Fujifilm APS-C (1.5×) → 34.5 mm equivalent — the classic reportage focal length.
- 56 mm on Fujifilm APS-C (1.5×) → 84 mm equivalent — which is why the 56 mm is the portrait lens.
- 25 mm on Micro Four Thirds (2.0×) → 50 mm equivalent — the normal focal length.
- 63 mm on Fujifilm GFX (0.79×) → about 50 mm equivalent — medium format converts downwards.
The other way round: to get the framing of a 35 mm full-frame lens on APS-C, you need 35 ÷ 1.5 ≈ 23 mm of real focal length.
Your iPhone for comparison
Phone cameras have tiny sensors — and correspondingly high crop factors. The main camera of current iPhone Pro models has a 35mm equivalent of about 24 mm with an actual focal length of only around 6.9 mm. That is a crop factor of roughly 3.5×.
- Ultra-wide (0.5×): ≈ 13 mm equivalent — extremely wide, for architecture and tight rooms.
- Main camera (1×): ≈ 24 mm equivalent — moderate wide angle, a solid all-rounder.
- 2× mode: ≈ 48 mm equivalent — a sensor crop of the main camera, the normal focal length.
- Telephoto (5×, Pro Max only): ≈ 120 mm equivalent — a real tele from a folded lens path.
The remarkable part: your iPhone fits "13 mm ultra-wide" through "120 mm tele" into 8 mm of body thickness. A full-frame 24–120 mm zoom weighs around 700 g and is 12 cm long. The tiny sensor makes it possible — at the cost of almost no background separation despite "f/1.8".
Crop factor and depth of field
Framing converts cleanly — background blur does not. Aperture and physical focal length stay the same, so depth of field at the same real focal length stays the same too. To get the same look as full frame on a smaller sensor (same framing AND same blur), you also have to open the aperture by the crop factor.
Example: 50 mm f/2.8 on APS-C frames like 75 mm on full frame — but the blur is closer to f/4. How focal length, aperture and sensor size actually affect depth of field is what the Depth of Field Calculator works out.
In practice: which focal length for what?
| 35mm equivalent | Character | Typical use |
|---|---|---|
| up to 16 mm | Extreme ultra-wide | Interior architecture, night sky, deliberate distortion |
| 16–24 mm | Ultra-wide | Landscape, architecture, tight interiors |
| 24–35 mm | Wide angle | Reportage, street, environmental portrait |
| 35–50 mm | Normal | Everyday, street — close to what the eye sees |
| 50–70 mm | Short tele | Half-length portrait, details, first separation |
| 85–105 mm | Portrait tele | Head-and-shoulders portrait with soft background |
| 135–200 mm | Tele | Stage, close sports, compressed landscape |
| 300 mm and up | Super tele | Wildlife, birds and sport from a distance |
Frequently asked questions
What is the crop factor?
It tells you how much smaller a sensor's field of view is compared to full frame / 35mm (diagonal 43.3mm). APS-C on Fujifilm, Sony and Nikon is 1.5×, Canon APS-C is 1.6×, Micro Four Thirds 2.0×. A 35mm lens on APS-C frames like 52.5mm on full frame.
How do I convert to 35mm equivalent?
Real focal length × crop factor. 23mm on Fujifilm APS-C: 23 × 1.5 = 34.5mm. 25mm on Micro Four Thirds: 25 × 2.0 = 50mm. On medium format (GFX, factor ≈ 0.79) you convert downwards: 63mm equals about 50mm equivalent.
What is the crop factor of an iPhone camera?
The main camera of current iPhone Pro models: about 24mm equivalent at roughly 6.9mm real focal length — a crop factor near 3.5×. Ultra-wide ≈ 13mm, 2× mode ≈ 48mm, Pro Max telephoto (5×) ≈ 120mm.
Does the crop factor change depth of field?
Framing changes, focal length and aperture physically do not. For the same look as full frame (same framing and same blur) you also open the aperture by the crop factor. That is why phone photos rarely look strongly blurred despite "f/1.8".
Which focal length do I need for portraits on APS-C?
The classic portrait tele is 85–105mm equivalent. On Fujifilm/Sony/Nikon APS-C (1.5×) that is about 56–70mm real focal length — hence the popular 56mm lenses. On Canon APS-C (1.6×) roughly 53–66mm, on Micro Four Thirds (2.0×) about 42–52mm.