How to Resize a Video on iPhone

The fastest way to resize a video on iPhone is to use the crop presets in Photos to set the aspect ratio, then export at the resolution your target format actually needs. Here's the workflow, and the distinction that trips most people up. Three different meanings hiding behind one word.

Open the free Video Resizer →

Resize a video on iPhone with the Photos crop presets

Open the clip in Photos, tap Edit, then open the crop tool. The presets include Square, Wallpaper, 9:16 and 5:7. Tap one to apply it, and Photos crops the frame to match rather than stretching or squashing the footage to fit. The lock icon in the top right unlocks the ratio if you need a custom frame instead of a preset. Useful when a platform's actual safe area doesn't line up exactly with any of the built-in options, and you'd rather set the crop by eye.

Aspect ratio, resolution and file size are three different things

"Resize" gets used for three different jobs, and mixing them up is why the same advice doesn't always work twice. The aspect ratio is the shape of the frame , square, vertical, widescreen , and it's what the Photos presets change. The resolution is how many pixels make up that frame, like 1080x1920, and it's set separately, usually at export. File size is a third variable entirely, driven by bitrate and codec rather than shape or pixel count, and it's what you'd actually be chasing if the real problem is a file too large to send or upload. A video can have exactly the right aspect ratio and still be the wrong resolution, or the right resolution and still be an unnecessarily large file. Each of the three needs its own fix.

A landscape clip cropped down to 9:16 in Photos also loses the sides of the original frame permanently. There's no way to recover them from the cropped file afterward, which is why it's worth keeping the source clip until you're sure the crop is final.

Editing in 9:16 from the start

Montaj edits and exports at 1080x1920 by default, so the video is already the right shape and resolution for vertical formats without a separate resizing pass at the end. That also means there's no cropping decision to make after the fact. The frame you're composing in while editing is the frame that ships. If you've resized a video on iPhone to 9:16 using the Photos presets, that's the same target frame Montaj starts from.