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Crop factor calculator

Find the equivalent full-frame focal length of a lens on a crop sensor.

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Enter Lens focal length (mm), Crop factor and the Crop factor calculator works out Equivalent focal length (mm) straight away. For instance, with Lens focal length (mm) = 50 and Crop factor = 1.5 it returns Equivalent focal length (mm) = 75.

How to use it

  1. Enter your values: Lens focal length (mm), Crop factor.
  2. Read the result instantly: Equivalent focal length (mm).

Frequently asked questions

What does the Crop factor calculator actually compute?

It takes Lens focal length (mm) and Crop factor and derives Equivalent focal length (mm) from them. The calculation is live as you type, so the result updates on every change.

What information do I need to provide?

2 values: Lens focal length (mm) and Crop factor. Nothing else is required — no account, no file upload.

Can you show a worked example?

With Lens focal length (mm) = 50 and Crop factor = 1.5, the calculator returns Equivalent focal length (mm) = 75. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

What happens if I enter larger values?

It moves a lot. Using Lens focal length (mm) = 55 and Crop factor = 3 instead, Equivalent focal length (mm) goes from 75 to 165 — which is why it is worth testing a few scenarios rather than trusting a single figure.

What does it give for smaller values?

Scaled down to Lens focal length (mm) = 45 and Crop factor = 0.75, Equivalent focal length (mm) comes out at 33.75. The relationship is worth checking at both ends before you rely on a single result.

When would I actually use this?

Finding out how big a thing will be before you make it: how many gigabytes an hour of footage takes, how long a file needs on the connection you have, how large a photo prints before it goes soft, what bitrate fits the budget you were given.

What is the most common mistake?

Reading a figure in one unit next to a figure in another. Megabits are not megabytes and the eight-fold gap sinks most transfer estimates; a kilobyte is 1 000 bytes to a drive maker and 1 024 to the operating system; pixels are not dots per inch. None of it is hard arithmetic — the unit on each side is what decides whether the answer means anything.

Where do the figures come from, and how current are they?

Byte prefixes follow the IEC convention where a kibibyte is 1 024 bytes and a kilobyte is 1 000 — drive makers use the second, operating systems often report the first, and a disk that shrinks on arrival is that gap and nothing else. Print sizing assumes 300 dpi unless you change it.

Further reading

All guides →
ExplainerCrop Factor: What It Changes and What It Does NotCrop factor is a ratio of sensor diagonals. It changes framing, not the lens — proved by computing field of view both ways — and it applies to the f-number as well as the focal length, which is the half most articles leave out.ExplainerThe Hyperfocal Distance Is Only as Precise as a Judgement CallA 50 mm lens at f/8 gives 10.47 m — or 15.68 m if you tighten the circle of confusion from 0.03 to 0.02 mm. Both settings are defensible and they differ by half.ExplainerDepth of Field: What Actually Controls ItFour variables set depth of field, and subject distance dominates the other three. The exact formulas, a computed table, why the circle of confusion is a decision rather than a measurement, and what "full frame has less depth of field" really means.ExplainerThe Exposure Triangle Is Three Routes to the Same StopA stop is a factor of two in light. The f-number scale is powers of √2 for a reason you can derive in one line, EV = log2(N²/t) puts a number on it, and the three controls are equivalent in brightness only — never in the picture.ExplainerWhat Is Bitrate? Bits per Second, CBR vs VBRBitrate is how many bits of data a video or audio stream uses each second. Learn how it sets quality and file size, and the difference between constant and variable bitrate.ExplainerHow Much Data Streaming Uses: SD, HD, and 4K per HourSee how many gigabytes per hour SD, HD, and 4K video use, and how to check a monthly streaming habit against a data cap.