Ratios worth knowing
| Ratio | Decimal | Where it comes from |
|---|---|---|
| 1:1 | 1.000 | Square. Rolleiflex and Hasselblad 6×6, then Instagram. |
| 5:4 | 1.250 | Large format 4×5 sheet film, and the 8×10 inch print. |
| 4:3 | 1.333 | Micro Four Thirds, medium format digital, every phone sensor. |
| 3:2 | 1.500 | 35 mm film — Leica cut two 18×24 cine frames side by side. |
| 16:9 | 1.778 | HDTV. A geometric compromise between 4:3 and 2.35:1. |
| 1.85:1 | 1.850 | Standard theatrical widescreen. |
| 2.39:1 | 2.390 | Modern anamorphic cinema, usually written 2.4:1. |
| 65:24 | 2.708 | Hasselblad XPan panoramic — three 35 mm frames wide. |
Crop in camera, or crop later?
The pixels are identical either way. The difference is what you saw while you were shooting.
Crop later and you keep every option, at the cost of composing inside a frame that is not the frame. Most people end up cropping to whatever saves the shot rather than to what they intended, because they never actually saw the intended one.
Crop in camera and the viewfinder shows the real edges. You compose to those edges, and the picture is finished when you press the shutter. The cost is the pixels you threw away and cannot get back — which is why a camera that crops in the viewfinder should show you the crop honestly, and why raw files are usually left uncropped even when the preview is not.
The viewfinder letterboxes to the ratio you picked, so what you see is exactly what saves. Processed files are cropped on save; raw files stay full-frame, because a negative should keep everything the sensor recorded.
Common questions
How do I calculate an aspect ratio?
Divide width by height for the decimal, then reduce both numbers by their greatest common divisor for the familiar form. 6000 × 4000 gives 1.5, and reduces to 3:2.
Does cropping reduce image quality?
It reduces resolution, not quality. Every surviving pixel is untouched. It only becomes a quality question when the smaller pixel count stops supporting your print size — check that with the print size calculator.
Why is 4:3 called portrait when it is wider than tall?
It is not — 4:3 is a landscape ratio. Rotate the camera and it becomes 3:4, which is what phones save when held upright. This calculator reports orientation for whichever way round you enter the numbers.
What ratio should I use for Instagram?
4:5 for the tallest feed post that will not be cropped, 1:1 for square, and 9:16 for stories and reels. Shoot wider than you need and crop with room to spare — every platform reserves the right to change its mind.
Is 2.35:1 the same as 2.39:1?
Nearly. 2.35:1 was the anamorphic standard until 1970; 2.39:1 replaced it and is what modern films use, usually printed as 2.40:1. Nobody will notice the difference; a projectionist would.
Related tools
A viewfinder that never lies.
Lucid letterboxes the live preview to your chosen ratio, so the gate you compose in is the file you get. Five ratios, and raw always stays full-frame.