Use the area your camera actually records
Start with the sensor width and height in your camera manual. For video, use the image area for the recording mode you selected. Some modes read a smaller area than the full sensor. Electronic stabilisation can crop it again. Enter that smaller area if you know its dimensions. Choose a recording shape only when you want a centred crop from the area you entered.
The two examples use Nikon's rounded 24 × 16 mm DX and 36 × 24 mm FX format sizes. They are format references, rather than exact measurements for every camera sold under those names. Enter custom dimensions from your model's specifications when the difference matters.
What the equivalent focal length tells you
A 35 mm lens stays a 35 mm lens when you change cameras. A smaller recorded area captures less of its image, so the view becomes narrower. The equivalent focal length describes the full-frame lens that would give a similar view. Nikon explains crop factor with the same comparison.
The large result matches the diagonal angle against a 36 × 24 mm frame. The horizontal equivalent matches width instead. With two different aspect ratios, these can differ: one focal length cannot match both the horizontal and vertical view. Read the three angle values when framing a particular shot.
Check a simple example
With a 24 × 16 mm area and a 35 mm lens, the crop factor is 1.50× and the diagonal equivalent is 52.5 mm. Change to a 36 × 24 mm area with the same lens and the crop factor becomes 1.00×. A 16:9 crop keeps the width of either example and trims the height, leaving the horizontal view unchanged.
Method and limits
The tool divides the 36 × 24 mm reference diagonal by the entered area's diagonal. It multiplies that ratio by your lens's focal length for the diagonal equivalent. Angle of view uses the rectilinear relationship 2 × arctan(image dimension ÷ twice the focal length). The calculation treats the lens as focused on a distant subject.
It does not model fisheye projection, lens distortion, anamorphic squeeze, focus breathing, close-focus extension or a camera's distortion correction. Use a test frame for an exact composition. Matching framing also says nothing about a lens's sharpness or a camera's noise, dynamic range or depth of field. For the creative choices behind a frame, see our visual storytelling guide.
Your entries stay in this browser when storage is available. Use Print result for a paper or PDF copy with the input values. Reset returns to the worked example. No sign-up is needed.