Online Tool Store
Lens Focal Length Calculator
Lens Focal Length Calculator gives the framing; the distance you shoot from is what sets the perspective, and that is a separate decision.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Image
Lens Focal Length Calculator
Frontend preview — no upload or external service.
Required focal length
Framing a 1.8 m subject vertically at 6 m on full frame needs about 80 mm. On APS-C the same framing needs roughly 53 mm.
How the Lens Focal Length Calculator works
- Enter the subject size and the distance you can work from.
- Choose the sensor format, which changes the answer substantially.
- Check the result against lenses you own — the calculation often shows that the constraint is the room, not the lens.
The method
Focal length, subject size, distance and sensor dimension are related by similar triangles.
focal length = (sensor dimension x distance) / subject size
This is why the same lens frames differently on different sensors, and why a smaller sensor needs a shorter focal length for identical framing.
FAQ
Does this account for crop factor?
Yes — sensor dimension is an input, so the answer is the actual focal length for that camera rather than a full-frame equivalent.
Why does my calculated lens not match what looks right?
Perspective. Focal length sets framing, but the distance you shoot from sets how features compress. The same framing at 3 m with a wide lens and at 8 m with a longer one look very different, which is why portrait distance matters.
What about focus breathing?
Some lenses change effective focal length slightly at close focus, so a marked 50 mm may frame like a 45 mm at minimum distance. It matters for macro and precise framing work.
How we compare
| Feature | Online Tool Store | A desktop editor | An upload-based service |
|---|---|---|---|
| Sensor-aware | ✓ | Full frame only | ✓ |
| Solves in any direction | ✓ | ✗ | ✓ |
| No sign-up | ✓ | ✓ | ✗ |
| Nothing uploaded | ✓ | ✓ | ✗ |
Lens Focal Length Calculator gives the framing; the distance you shoot from is what sets the perspective, and that is a separate decision.