The Focal Width/Length Calculator is a practical tool used in photography, optics, and imaging systems to determine the actual width of a scene or subject that will appear in the frame at a given distance from the camera or lens. This helps users predict how much of a subject will fit into the frame, adjust composition, and select the right focal length for their needs.
This calculator belongs to the Photography and Imaging Optics category. It is especially useful for photographers, videographers, industrial imaging technicians, and engineers who need to control the field of view with precision. Whether working with drones, microscopes, security cameras, or cinema lenses, knowing the correct focal width can lead to better results in capturing or inspecting a subject.
Formula of Focal Width/Length Calculator
There are several ways to calculate focal width depending on the available data:
- Field Width (Linear Field of View):
Field Width (W) = 2 × f × tan(θ / 2)
Where:
W = Field width or focal width (in meters, millimeters, etc.)
f = Distance from the lens (focal length or object distance)
θ = Angle of view in degrees (horizontal, vertical, or diagonal)
- Angle of View from Field Width:
θ = 2 × arctangent(W / (2 × f))
- Imaging Systems (Sensor-Based Width):
Field Width (W) = (Sensor Width × Subject Distance) / Focal Length
Where:
Sensor Width = Physical width of the sensor (e.g., 36 mm for full-frame)
Subject Distance = Distance to the object or subject
Focal Length = Lens focal length in mm
These formulas allow users to go in either direction: calculate the field width based on distance and angle, or determine angle based on width and distance.
Common Sensor and Focal Length Reference Table
| Sensor Type | Sensor Width (mm) | Subject Distance (m) | Focal Length (mm) | Approx. Field Width (m) |
|---|---|---|---|---|
| Full Frame (35mm) | 36 | 5 | 50 | 3.6 |
| APS-C (Nikon/Sony) | 23.6 | 3 | 35 | 2.03 |
| Micro Four Thirds | 17.3 | 2 | 25 | 1.38 |
| 1-Inch Sensor | 13.2 | 1.5 | 20 | 0.99 |
| Super 35 Video | 24.89 | 4 | 50 | 1.99 |
This table offers quick lookup values to avoid manual calculation and supports fast planning in field photography or studio setups.
Example of Focal Width/Length Calculator
Let’s say you are using a full-frame camera with a 50mm lens and want to find out how much width of the scene will appear in your frame at a distance of 5 meters from your subject.
Use the formula:
W = (36 × 5) / 50
W = 180 / 50 = 3.6 meters
This means your frame will cover a scene that is 3.6 meters wide.
Alternatively, if you want to calculate the angle from a known width:
θ = 2 × arctangent(3.6 / (2 × 5))
θ = 2 × arctangent(0.36) ≈ 39.6 degrees
This gives a horizontal angle of view of about 39.6°.
Most Common FAQs
Focal width, also known as field width, is the actual horizontal or vertical area visible through a camera or lens from a specific distance.
Yes, larger sensors will display more of the scene at the same focal length, giving a wider field width compared to smaller sensors.
Absolutely. This calculator works for still photography and moving image formats, including cinematic sensors like Super 35 or Micro Four Thirds.