Equivalent Focal Length
Focal length on a crop sensor expressed in full-frame terms.
Formula
Live Calculator
MembersVariables
Example
35 mm lens, 1.6× crop: f_eq = 56 mm
How it works
Equivalent focal length lets you compare how a lens will frame a scene on different camera sensor sizes by converting the actual lens focal length into a full-frame reference. The crop factor does not change the lens itself; it changes how much of the image circle is recorded, so the field of view becomes narrower on smaller sensors. This formula works because the crop factor scales the angle of view relative to a full-frame camera.
When to use it
Use this when comparing lenses across different camera systems, especially when shopping for a camera or estimating how wide a shot will look. It is also helpful for planning travel, portrait, wildlife, or sports photography where field of view matters.
Worked example, step by step
A camera uses a 24 mm lens and has a crop factor of 1.5. Use the formula: f_eq = f × C Substitute the values: f_eq = 24 × 1.5 Calculate: f_eq = 36 So the equivalent focal length is 36 mm.
Common mistakes to avoid
- Multiplying by crop factor and treating it as the lens's true focal length
- Using equivalent focal length to change aperture or brightness calculations
- Forgetting that crop factor depends on sensor size, not on the lens
Did You Know?
An APS-C sensor's 1.5–1.6× crop factor turns a cheap 50 mm into a portrait-friendly ~80 mm.
Share this formula
More in Photography & Imaging
View allF-Number
BasicAperture f-number is focal length divided by aperture diameter.
Exposure Value (EV)
IntermediateCombines aperture and shutter speed into one exposure figure.
Depth of Field (approx.)
AdvancedRange of distances that appear acceptably sharp.
Hyperfocal Distance
AdvancedFocus distance that keeps everything from H/2 to infinity sharp.
Lens Magnification
IntermediateImage magnification from focal length and subject distance.
Angle of View
IntermediateField of view from sensor size and focal length.