Calculating your full-frame equivalent focal length is straightforward once you know the Crop Factor formula and what each input means. This guide explains the method in plain language, walks through a manual calculation, and gives worked examples you can follow — then you can do it instantly with the Crop Factor Calculator.
What is Crop Factor?
The Crop Factor calculation tells you your full-frame equivalent focal length from a few simple inputs. The figure you are solving for here is the full-frame equivalent focal length.
The Crop Factor formula
The core formula is:
Full-frame equivalent focal length = Lens focal length × Crop factorHere is what each input means:
- Lens focal length — a value measured in mm. Example: 50 mm.
- Crop factor — a number. Example: 1.5.
How to calculate it step by step
- Write down the lens focal length (for example, 50 mm).
- Write down the crop factor (for example, 1.5).
- Apply the formula above to get your full-frame equivalent focal length.
- Double-check the result with the Crop Factor Calculator.
Worked examples
Example 1
| Input / Output | Value |
|---|---|
| Lens focal length | 50 mm |
| Crop factor | 1.5 |
| Full-frame equivalent focal length | 75.0 |
With lens focal length of 50 mm and crop factor of 1.5, the full-frame equivalent focal length works out to 75.0.
Example 2
With lens focal length of 100 mm and crop factor of 1.5, the full-frame equivalent focal length works out to 150.0.
| Result | Value |
|---|---|
| Full-frame equivalent focal length | 150.0 |
Example 3
With lens focal length of 25 mm and crop factor of 1.5, the full-frame equivalent focal length works out to 37.5.
| Result | Value |
|---|---|
| Full-frame equivalent focal length | 37.5 |
Tips for an accurate result
- Keep your units consistent — mixing, say, months with years or grams with kilograms is the most common source of error.
- Round only at the very end. Rounding inputs early can shift the final answer noticeably.
- Re-run the numbers whenever an input changes, rather than estimating from an old result.
Prefer not to do the maths by hand? — the Crop Factor Calculator does it instantly, for free, with the formula and a worked example built in.
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