Aspect ratio calculator
Drop a clip and the calculator reads its real width and height in your browser, then returns the simplified ratio and the exact centered crop each format keeps — 9:16 for TikTok, Reels and Shorts, 4:5 and 1:1 for feeds, 16:9 for YouTube. Nothing uploads.
Given your own file's dimensions, produce the simplified ratio and the exact crop each platform format keeps, in under two seconds.
or type them
16:9 (1.7778) · from a 4K 16:9 camera master
| target | crop from your frame | export | keeps |
|---|---|---|---|
| 9:16 — Reels, TikTok, Shorts | 1215×2160 centered | 1080×1920 | 32% |
| 4:5 — Instagram portrait | 1728×2160 centered | 1080×1350 | 45% |
| 1:1 — square feed | 2160×2160 centered | 1080×1080 | 56% |
| 16:9 — YouTube | 3840×2160 centered | 1920×1080 | 100% |
You know what each format keeps. You do not know where the subject sits inside it — that is a framing decision, made per shot, on every clip you cut.
Next artifact: the reframe.
Never measures the face in each shot and moves the 9:16 window to follow it, then exports the same cut at every ratio in this table from one source file.
See the measured reframeYour file is read by your browser to get its width and height, and released straight away. Nothing uploads, nothing is stored, and there is nothing to delete.
What the aspect ratio calculator is measuring
Every reformat is a negotiation between what you shot and what the platform shows full-screen, and the aspect ratio calculator makes the negotiation explicit: it prints how much of your frame each target keeps, in your own pixels. That number is the honest input to decisions you make before you roll — where the camera sits, how wide the shot is, and how much headroom a vertical crop can afford to throw away.
The reason the tool asks for your file rather than a menu of stock resolutions is that stock resolutions answer a question about a hypothetical video. A 5.7K open-gate mirrorless master, a 2532×1170 screen recording and a 1080×1920 phone clip all crop differently, and only one of them is yours.
How to work out an aspect ratio crop by hand
- Read the real dimensions. Open the file's properties, or the clip's info panel in your editor. Use the stored pixel dimensions, not the timeline's — a 4K clip on a 1080p timeline is still 4K.
- Simplify. Divide both numbers by their greatest common divisor. 3840 and 2160 share 240, so the ratio is 16:9.
- Fit the target. Scale the target ratio up until one side matches yours. For 9:16 inside 3840×2160, height is the binding side: 2160 tall means 2160 × 9 / 16 = 1215 wide.
- Check the loss. 1215 of 3840 pixels is 32% of the width. Everything else is outside the vertical frame — including, usually, one of the two people in a two-shot.
Where the manual way breaks
The arithmetic takes a minute. Doing it for every deliverable does not: one recording that ships as a 16:9 long-form, eight 9:16 clips and a 4:5 feed post is ten separate crop decisions, and the crop is only the first of them — each one still needs a subject position. The Editing Tax dataset puts reframing and exporting a single vertical deliverable at 15 minutes of the 390 minutes one 12-minute recording costs, and that line repeats per clip, not per recording.
The other failure is silent. A centered crop is correct only when the subject is centered, and a talking head who drifts left over 40 minutes produces a vertical clip with a shoulder in it. Never measures the subject in each shot and moves the crop window to follow, which is the measured reframe — the same arithmetic on this page, applied per shot instead of per project.
Read the transcript
Aspect ratio calculator Drop a clip and the calculator reads its real width and height in your browser, then returns the simplified ratio and the exact centered crop each format keeps — 9:16 for TikTok, Reels and Shorts, 4:5 and 1:1 for feeds, 16:9 for YouTube. Nothing uploads.
Frequently asked questions
What does 'crop from your frame' mean in the results?
The largest window of your source that matches the target ratio. A 3840×2160 source contains a 1215×2160 window at 9:16 — that window scales to 1080×1920 cleanly. Anything outside it is what a vertical crop gives up.
Why does shooting 4K matter for vertical clips?
A 9:16 crop keeps about a third of a 16:9 frame's width. From 4K that third is still sharper than a 1080×1920 export needs; from a 1080p source it has to upscale. If vertical clips are a primary output, record 4K.
Does my file leave the browser?
No. The calculator reads the file's intrinsic width and height with the browser's own metadata reader and releases it immediately. There is no upload, no storage and nothing to delete.