Crop Factor Calculator

Frequently Asked Questions

What is crop factor?

The ratio of a full-frame sensor's diagonal (43.27 mm) to your sensor's diagonal. APS-C is ~1.5–1.6×, Micro Four Thirds 2×, 1-inch ~2.7×. It scales how a lens "sees" relative to full frame.

How do I get equivalent focal length?

Multiply the lens focal length by the crop factor: a 50 mm on a 1.5× APS-C body frames like a 75 mm on full frame. The tool also gives equivalent aperture (f × crop) for depth-of-field and light-gathering comparisons.

Does crop factor change aperture or exposure?

Exposure (brightness) does not change - f/2.8 is f/2.8 on any sensor. But depth of field and total light collected match a larger f-number on full frame, which is the "equivalent aperture".

Is a crop sensor worse?

No - just different. Crop bodies give extra reach for wildlife/sports and smaller, cheaper lenses; full frame gives wider angle and shallower DOF for the same framing.

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Estimates for informational purposes only.

Important Disclaimer: Estimates for informational purposes only.

This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

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How This Calculator Works

The crop factor (focal length multiplier) compares a sensor's diagonal to that of a 35mm full−frame sensor, which measures 36 × 24 mm for a diagonal of √(36² + 24²) ≈ 43.27 mm. The crop factor is simply crop = 43.27 ÷ sensor diagonal. From it we derive the 35mm−equivalent focal length (focal × crop), the equivalent aperture for depth of field and total light gathering (f−number × crop), and a matching ISO offset. Enter a sensor preset or custom dimensions plus a real lens focal length and aperture.

Worked Example

A 23.5 × 15.6 mm Sony APS−C sensor has a diagonal of √(23.5² + 15.6²) ≈ 28.2 mm, so crop = 43.27 ÷ 28.2 ≈ 1.53. A 50 mm f/1.8 lens behaves like a 50 × 1.53 ≈ 76 mm lens framing−wise. For depth of field and gathered light it is equivalent to roughly f/1.8 × 1.53 ≈ f/2.8 on full−frame - the same composition but less background blur and about 1.3 stops less total light on the sensor.

Real-World Use

Crop factor explains why a 35 mm lens is the "standard" lens on APS−C (it frames like a 50 mm), why Micro Four Thirds wildlife shooters love that a 300 mm reaches like 600 mm, and why phone cameras with tiny sensors need ultra−short actual focal lengths to deliver a normal field of view. Use the equivalent focal length when planning framing across systems, and the equivalent aperture when comparing how blurred a background will look.

Common Mistakes

Aperture light per area does not change. An f/1.8 lens still meters as f/1.8 for exposure; only total light on the whole sensor and the depth of field scale with crop.

Crop does not magnify or zoom. It only changes the field of view by recording a smaller portion of the projected image circle.

Different APS−C sizes. Canon APS−C (×1.6) is smaller than Nikon/Sony (×1.5); always pick the right preset.

Limitations & Related Tools

This is a pure geometric ratio: it ignores lens distortion, image−circle vignetting, and pixel−level resolution differences. Equivalent aperture describes depth of field and total light, not diffraction, which depends on the physical f−number. Pair this with a depth−of−field calculator to see exact near and far limits, and a sensor−size comparison when choosing a system. Treat the numbers as an accurate planning guide rather than an optical guarantee for a specific lens design.

Frequently Asked Questions

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