Lens Crop Factor Calculator

Crop factor (also called the focal length multiplier) describes how a camera sensor’s size compares to the gold-standard 35mm full-frame sensor. Smaller sensors capture a narrower slice of the image circle projected by the lens, effectively “cropping” the scene — which makes any given lens behave like a longer focal length.

Core formula: Equivalent Focal Length = Actual Focal Length × Crop Factor

Crop factor itself is derived from: Crop Factor = Diagonal of 35mm sensor ÷ Diagonal of your sensor

35mm full-frame diagonal = √(36² + 24²) = 43.27 mm

So an APS-C sensor (23.5 × 15.6 mm, diagonal = 28.2 mm) gives: 43.27 ÷ 28.2 = 1.53× (rounded to 1.5×).

Common crop factors by sensor type:

• Full Frame (35mm): 1.0×, 36 × 24 mm
• APS-C (Nikon/Sony/Fuji): 1.5×, 23.5 × 15.6 mm
• APS-C (Canon): 1.6×, 22.3 × 14.9 mm
• Micro Four Thirds (Olympus/Panasonic): 2.0×, 17.3 × 13 mm
• 1-inch sensor (Sony RX100): 2.7×, 13.2 × 8.8 mm
• Smartphone (1/2.55″): ~5.6×, varies by model

What crop factor changes — and what it does NOT:

• Field of view: Narrows. Your 50mm lens frames like a 75mm on APS-C 1.5×.
• Depth of field: Effectively deeper at identical framing and aperture, because you must stand farther from the subject.
• Equivalent aperture for DoF: Multiply actual f-stop × crop factor. An f/1.8 lens on APS-C behaves like f/2.7 on full frame for depth of field, but NOT for exposure. Exposure is unaffected by sensor size.
• Light gathering per pixel: Does NOT change. Sensor size affects total light per frame, but exposure math (ISO, shutter, aperture) remains the same.

Worked example: You own a 24–70mm f/2.8 zoom and shoot with a Nikon APS-C body (crop factor 1.5×).

• At 24mm → equivalent 36mm (wide-angle, good for interiors)
• At 70mm → equivalent 105mm (short telephoto, ideal for portraits)
• Your effective zoom range on full frame framing: 36–105mm

This is why APS-C bodies are popular for wildlife and sports: a 300mm telephoto becomes an effective 450mm without buying an expensive supertele.

Reverse calculation — finding the actual focal length that mimics a full-frame focal length: Actual FL = Desired Equivalent FL ÷ Crop Factor To get 85mm portrait framing on a 2× Micro Four Thirds body, use a 42.5mm lens.