How to use
- Enter the active sensor width and height in millimetres. The reference format is fixed at 36 × 24 mm, the usual full-frame or 35 mm still-photo frame.
- Enter the actual focal length of your lens. Calculate to obtain the sensor diagonal, crop factor and equivalent focal length.
- Use the solid and dashed sensor outlines to compare physical recording areas. Both rectangles share one scale and are centred; their positions do not describe how a real sensor is mounted.
The initial values are editable examples, not detected camera settings. Enter plain numbers with a decimal point or decimal comma and without thousands separators. The range below each field states the supported limits. Press Calculate, or Enter in a field, to confirm the current inputs. The diagram above the fields updates immediately with valid settings, including the starting example. Editing clears the confirmed Result and Copy state; press Calculate to confirm again. Incomplete or invalid settings remove the preview geometry. Clear empties the numeric inputs, result and diagram; it keeps the calculation selection. Copy result copies the displayed values with labels. Calculations stay in your browser. Changing the site language opens a translated page and asks before leaving your current inputs; it does not convert a saved camera configuration.
Calculation and interpretation
A crop factor calculator expresses sensor size relative to a familiar reference. It is useful when comparing camera formats or interpreting a lens description. The equivalent focal length answers a specific question: what focal length on a 36 × 24 mm camera would give the same diagonal angle of view as this lens on this sensor? It is a comparison of framing, not a modification of the lens.
Sensor diagonal d = √(width² + height²). Reference diagonal = √(36² + 24²), approximately 43.27 mm. Crop factor k = reference diagonal / d. Equivalent focal length = actual focal length × k. The calculation keeps the unrounded diagonal and factor internally; the displayed two-decimal values are not used as intermediate inputs.
The diagram shows the entered sensor as a solid outline and the reference as a dashed outline at a common scale. A smaller solid rectangle gives a crop factor above one. A larger sensor gives a factor below one. If the sensors have different aspect ratios, diagonal equivalence does not imply identical horizontal and vertical framing: one rectangle may be relatively wider or taller.
Worked examples
For a 24 × 16 mm sensor and a 50 mm lens, the sensor diagonal is about 28.84 mm. Crop factor is exactly 1.5 and the equivalent focal length is 75 mm. A 75 mm lens on the reference format gives the same diagonal angle under the rectilinear, distant-focus assumption.
For a 36 × 24 mm sensor with a 35 mm lens, crop factor is one and equivalent focal length stays 35 mm. As a larger-format comparison, a 48 × 32 mm sensor has a factor of 0.75, making a 50 mm lens equivalent to 37.5 mm. These examples show why crop factor is not always greater than one.
Practical uses and limits
Use equivalence to compare fields of view when planning a lens kit, reading reviews or moving between camera systems. Enter measured or manufacturer-specified active dimensions rather than assuming every APS-C or phone sensor is the same size. A video crop changes the relevant dimensions even when the physical camera and lens remain unchanged.
The actual focal length, entrance pupil and lens aperture do not change when a sensor is smaller. This page does not convert aperture, calculate depth of field, predict noise, or assess lens resolution. It also does not check whether a lens image circle covers a given sensor. An equivalent focal length is not a recommendation to buy or mount that lens.
Perspective depends on camera position relative to the scene. If you stay in the same place, changing sensor coverage crops the view without changing those perspective relationships. If you move to recover the same subject framing, perspective changes because the viewpoint moved. Equivalence alone cannot describe that second situation.
Frequently asked questions
Does a crop sensor turn my 50 mm lens into a 75 mm lens?
No. On a 1.5× crop sensor it gives a diagonal view comparable to 75 mm on full frame, but the lens’s actual focal length remains 50 mm.
Can I enter a sensor larger than full frame?
Yes. Dimensions from 0.1 to 500 mm are accepted. A larger diagonal produces a factor below one; the diagram expands its shared scale to keep both sensors visible.
Why does a quoted factor differ slightly?
Manufacturers often round crop factors and equivalent focal lengths. Active area, video cropping and aspect ratio can also differ. Compare the underlying dimensions before treating a small difference as an error.
Do matching equivalents produce identical photographs?
No. They compare diagonal framing under the model. Aspect ratio, viewpoint, lens rendering, aperture, focusing and processing can still produce different pictures.