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Equivalent Focal Length Calculator

Convert a lens focal length to its 35mm-equivalent field of view.

Introduction

Equivalent Focal Length Calculator — Convert a lens focal length to its 35mm-equivalent field of view. Enter Actual Focal Length, Sensor Width, Sensor Height to get an instant, accurate result.

Formula

Sensor diagonal = √(width² + height²). Crop factor = 43.3 / sensor diagonal (43.3mm is the 35mm full-frame diagonal). Equivalent focal length = actual focal length × crop factor.

Step-by-step

  1. Enter the Actual Focal Length.
  2. Enter the Sensor Width.
  3. Enter the Sensor Height.
  4. Click Calculate to see your result instantly.

Real-world example

Example: With Actual Focal Length = 50 mm, Sensor Width = 23.5 mm, Sensor Height = 15.6 mm, the Equivalent Focal Length Calculator gives Sensor Diagonal Mm: 28.2066, Crop Factor: 1.5351, Equivalent Focal Length: 76.7552.

Frequently Asked Questions

Why use 43.3mm as the reference?
That's the diagonal of a standard 35mm full-frame sensor (36mm × 24mm), the reference point photographers use to compare fields of view across different sensor sizes.
Does this change the lens's actual focal length?
No — the physical focal length is unchanged; the equivalent value only describes the field of view you'd get from that same focal length on a full-frame camera.
What inputs does the Equivalent Focal Length Calculator need?
You'll need to provide: Actual Focal Length, Sensor Width, Sensor Height. All fields use sensible defaults, so you can see a working example immediately and then adjust the values to match your own numbers.
How accurate is the Equivalent Focal Length Calculator?
The Equivalent Focal Length Calculator applies the formula exactly as calculated — Sensor diagonal = √(width² + height²). Crop factor = 43.3 / sensor diagonal (43.3mm is the 35mm full-frame diagonal). Equivalent focal length = actual focal length × crop factor. — so results are precise for the inputs you provide. Accuracy depends on entering correct, realistic input values.
Is the Equivalent Focal Length Calculator free to use?
Yes, the Equivalent Focal Length Calculator is completely free, requires no signup, and runs instantly in your browser.

About the Equivalent Focal Length Calculator

The Equivalent Focal Length Calculator uses a real, verifiable formula — Sensor diagonal = √(width² + height²). Crop factor = 43.3 / sensor diagonal (43.3mm is the 35mm full-frame diagonal). Equivalent focal length = actual focal length × crop factor. — so results are accurate every time, not an approximation.