Should I save at more than 1080 pixels wide if I can?

Not for anything that is going straight to a social app. Every one of them re-encodes what you send and most target around 1080 on the short edge, so a larger file is compressed harder on their side rather than arriving sharper. Where a bigger file does earn its place is printing or a website of your own, and this tool does not yet output the print proportions — that is honest rather than modest.

Why does my square collage get cut off as a display picture?

Because a display picture is a circle cut out of a square, and the corners of your collage are outside that circle. On a nine-slot grid that removes a bite from four of the nine pictures. If the collage is destined for a profile photo, use a layout whose interesting slots are in the middle, or push the outer edge slider up so the whole arrangement sits inside the circle.

Is the tall post really better than the square?

It occupies about a quarter more screen height as somebody scrolls, which is the only mechanical advantage and it is a real one. What it costs is width per slot: at 1080 by 1350 the layouts get taller cells, so a wide landscape has less room to be wide in. If your pictures are mostly portraits the tall post is the better pick twice over; if they are mostly landscapes the square usually wins.

What size is right for a WhatsApp status?

The story shape, 1080 by 1920. A status is displayed full-screen on a phone in the same proportion, so anything squarer gets letterboxed with a blurred or plain band above and below. For a WhatsApp display picture it is the square you want instead, for the same circular-crop reason as anywhere else.

Can I make one collage and post it in all three shapes?

Yes, and it is three taps. Changing shape re-lays the collage through the arrangement drawn for that shape, keeping your photos in their slots and their framing intact, so you can save the square, switch to the story, save that, and switch again. Each save is a separate file and neither one is a crop of the other — they are genuinely different arrangements of the same pictures.

Which collage size for which app

Three shapes cover almost everything a phone posts. The differences between them are not cosmetic — each one changes how much room every slot in your collage gets.

The three shapes, in pixels

Aspect ratios are easy to say and hard to picture, so here they are as the numbers this tool actually writes. Every output is 1080 pixels on its short edge, which is what the apps compress towards; the long edge is what changes.

Output sizes and where they land
Shape	Pixels	Long edge vs square
Square 1:1	1080 × 1080	—
Tall post 4:5	1080 × 1350	25% taller
Story 9:16	1080 × 1920	78% taller

A story is nearly twice the height of a square at the same width, and that is why the layouts are drawn three times rather than reflowed. Three columns across a square are 344 pixels wide and perfectly reasonable; the same three columns down a story would be 344 by 1900, which is not a collage, it is a barcode.

What each destination takes off

Feeds

A feed post keeps the whole picture. What varies is how much of the screen it gets: a square takes its width in height, a 4:5 takes a quarter more. Nothing is cropped and nothing is at risk, so the choice here is purely about how much room you want to occupy against how wide each slot needs to be.

Full-screen stories and statuses

These are shown edge to edge on a phone, with the app’s own controls on top: a name and progress bar across the top, a reply field across the bottom. Budget around 250 pixels at each end as covered. A collage whose top slot runs to the frame edge will have part of that slot behind the furniture — push the outer edge slider to forty or so and the whole arrangement pulls clear.

Display pictures

Every one of them is a circle cut from a square, so the four corners are removed and roughly a fifth of the area goes with them. Square shape, centre-weighted layout, and nothing important in a corner slot. This is the one case where an even grid is actively the wrong choice.

Questions the sizes raise

Should I save at more than 1080 pixels wide if I can?: Not for anything that is going straight to a social app. Every one of them re-encodes what you send and most target around 1080 on the short edge, so a larger file is compressed harder on their side rather than arriving sharper. Where a bigger file does earn its place is printing or a website of your own, and this tool does not yet output the print proportions — that is honest rather than modest.
Why does my square collage get cut off as a display picture?: Because a display picture is a circle cut out of a square, and the corners of your collage are outside that circle. On a nine-slot grid that removes a bite from four of the nine pictures. If the collage is destined for a profile photo, use a layout whose interesting slots are in the middle, or push the outer edge slider up so the whole arrangement sits inside the circle.
Is the tall post really better than the square?: It occupies about a quarter more screen height as somebody scrolls, which is the only mechanical advantage and it is a real one. What it costs is width per slot: at 1080 by 1350 the layouts get taller cells, so a wide landscape has less room to be wide in. If your pictures are mostly portraits the tall post is the better pick twice over; if they are mostly landscapes the square usually wins.
What size is right for a WhatsApp status?: The story shape, 1080 by 1920. A status is displayed full-screen on a phone in the same proportion, so anything squarer gets letterboxed with a blurred or plain band above and below. For a WhatsApp display picture it is the square you want instead, for the same circular-crop reason as anywhere else.
Can I make one collage and post it in all three shapes?: Yes, and it is three taps. Changing shape re-lays the collage through the arrangement drawn for that shape, keeping your photos in their slots and their framing intact, so you can save the square, switch to the story, save that, and switch again. Each save is a separate file and neither one is a crop of the other — they are genuinely different arrangements of the same pictures.

What is not here yet

There is no 16:9 and no 3:2 in this version, which means no landscape output and nothing sized for a 6 by 4 print. Both are arrangements that have to be drawn rather than derived, and drawing thirty more maps properly takes longer than saying so does. Until they exist, a collage made here is a phone-shaped object and printing one will mean cropping it somewhere else.