Crop Factor Calculator

Crop factor is a key concept in photography that describes how a camera sensor compares in size to a full-frame 35 mm sensor. When a sensor is smaller than full frame, it captures only the center portion of the image circle projected by the lens — effectively 'cropping' the frame. This has practical consequences for focal length, depth of field, and angle of view that every photographer should understand when choosing lenses and camera bodies.

What Is Crop Factor?

The crop factor (also called the focal length multiplier) is the ratio of the full-frame 35 mm sensor diagonal (approximately 43.3 mm) to the diagonal of the smaller sensor. A sensor with a 1.5× crop factor has a diagonal roughly 1.5 times shorter than full frame. Common crop factors include 1.5× for Nikon and Sony APS-C sensors, 1.6× for Canon APS-C, 2.0× for Micro Four Thirds cameras, and 2.7× for 1-inch sensors found in many compact cameras and drones.

A full-frame sensor itself has a crop factor of exactly 1.0×, which is why it serves as the reference standard. Medium format sensors are actually larger than full frame, meaning they have a crop factor below 1.0× — sometimes called a magnification factor instead.

Equivalent Focal Length

The most commonly discussed effect of crop factor is on field of view. When a 50 mm lens is mounted on an APS-C body with a 1.5× crop factor, it produces the same angle of view as a 75 mm lens on a full-frame body (50 × 1.5 = 75 mm equivalent). This means a telephoto lens effectively becomes even more telephoto, which is often an advantage for wildlife and sports photographers who want extra reach.

However, it is important to note that the focal length of the lens itself does not change. A 50 mm lens is always a 50 mm lens regardless of the sensor it is mounted on. What changes is the captured field of view, not the optical properties of the glass. The 'equivalent focal length' is simply a way of communicating what focal length on a full-frame camera would yield the same angle of view.

Crop Factor and Depth of Field

Crop factor also affects apparent depth of field (DoF) when comparing the same scene framed identically. To frame a subject the same way on a cropped sensor as on full frame, you either use a shorter focal length or step further back. Both of these adjustments produce more depth of field compared to the full-frame setup.

The equivalent aperture formula — multiplying your actual f-stop by the crop factor — shows what f-stop on a full-frame camera would produce a similar depth of field. For example, shooting at f/2.8 on a camera with a 2.0× crop factor is roughly equivalent to f/5.6 on full frame in terms of background blur. This is why full-frame cameras are often favored for portrait photography where shallow depth of field and smooth bokeh are desired.

It is crucial to remember that this calculation applies only to depth of field, not to exposure. The exposure of your image depends on the f-stop number, shutter speed, and ISO, regardless of sensor size. Shooting at f/2.8 gives the same exposure on any sensor size.

Crop Factor and Angle of View

Angle of view is the angular extent of the scene that the camera captures, measured diagonally across the frame. A wider angle of view captures more of the scene, while a narrower angle isolates a smaller portion. The angle of view is determined by both the focal length and the sensor size.

This calculator uses the full-frame equivalent focal length to compute the diagonal angle of view based on the 35 mm full-frame sensor diagonal of approximately 43.3 mm. For instance, a 24 mm equivalent focal length produces a diagonal angle of view of roughly 84°, while a 200 mm equivalent produces about 12°. Wide-angle lenses generally have angles of view above 60°, while telephoto lenses have angles below 30°.

Practical Implications for Lens Choice

Understanding crop factor is essential when selecting lenses for a crop sensor camera. If you want a wide-angle perspective on an APS-C 1.5× camera, you need a lens with a focal length around 10–12 mm to achieve the same look as a 15–18 mm lens on full frame. Conversely, a standard 50 mm lens becomes a short portrait telephoto equivalent to 75 mm — a very useful focal length for portraits.

Some lenses are specifically designed for crop sensors (often labeled DX, EF-S, or similar) and project a smaller image circle. These lenses cannot be used on full-frame bodies without vignetting, but they are typically lighter, smaller, and less expensive than their full-frame counterparts. Other lenses are designed for full frame and can be used on both crop and full-frame bodies.

When planning a lens kit, it helps to think in terms of the full-frame equivalent focal lengths you need — for example, a wide zoom covering 16–35 mm equivalent, a standard zoom covering 24–70 mm equivalent, and a short telephoto zoom covering 70–200 mm equivalent — and then work backward to find the appropriate focal lengths for your specific sensor.

Crop Factor in Video

Many cameras apply an additional crop factor when shooting video, particularly at higher resolutions or frame rates. For example, a camera that has no crop in full-frame photo mode might apply a 1.5× or 1.74× crop in 4K video mode. This can significantly change the field of view compared to what you see in the viewfinder or when shooting stills. Always check your camera's specifications for the specific crop factor applied in each video mode.