Camera Focal Length Calculator
Focal Length Is a Number; Field of View Is What You See
Focal length in millimeters tells you almost nothing on its own — a 50 mm lens is "normal" on a full-frame body but distinctly telephoto on a smartphone sensor. What actually determines how much of a scene fits in the frame is the angle of view, which depends on both focal length and sensor width. This calculator converts between the two directly, so you can go from a lens spec to a field-of-view number, or work backward from a field of view you need to the focal length that delivers it.
The Formula
Focal Length = Sensor Width / (2 × tan(Angle of View / 2))
This calculates the horizontal angle of view using sensor width; the same formula applies to vertical or diagonal angle of view by substituting sensor height or sensor diagonal respectively.
Where This Calculation Matters
- Choosing a lens for a space — real estate and interior photographers work out the angle of view needed to fit a room before buying or renting glass.
- Event and venue planning — predicting how much of a stage or venue a given lens will capture from a fixed camera position.
- Cross-format comparisons — translating a focal length between sensor sizes by matching angle of view rather than the millimeter number alone.
- Video and cinematography — framing shots consistently across cameras with different sensor widths.
Angle of View by Focal Length (Full-Frame Sensor)
| Focal length | Horizontal angle of view |
|---|---|
| 14 mm | 104.3° |
| 24 mm | 73.7° |
| 35 mm | 54.4° |
| 50 mm | 39.6° |
| 85 mm | 23.9° |
| 100 mm | 20.4° |
| 200 mm | 10.3° |
On a cropped sensor, the same focal length produces a narrower angle of view — use the actual sensor width for your camera, not the full-frame figures above, for an accurate result.
How to Use This Calculator
- Choose a mode: Find Angle of View or Find Focal Length.
- Enter the sensor width in millimeters (36 mm for full frame; check your camera's specification for other formats).
- In Find Angle of View mode, enter the lens focal length in millimeters.
- In Find Focal Length mode, enter the angle of view you want, in degrees.
- Select Calculate to get the result.
Related Calculations
To convert a focal length between sensor formats directly, use the Camera Crop Factor Calculator. For how focal length affects the sharp zone in a shot, see the Hyperfocal Distance Calculator.