The Best Instagram Image Size for Organic Posts and Ads in 2026

Optimise Your Instagram Post Image Sizes (And Stop Leaving Attention on the Table)

Most people upload their Instagram images at whatever size their phone or design tool spits out. But if you’re using the wrong dimensions, you’re handing free screen real estate to everyone else in the feed — and on Instagram, screen space is attention, and attention is everything.

Here’s what you need to know.

The three formats you’ll encounter

Instagram feeds display posts in three main aspect ratios, and they are not created equal.

The square format (1:1, 1080 x 1080 pixels) is the most common format on the platform, but it’s actually the worst performer for screen coverage. Because it’s smaller than the other options, there’s more unused space around it, which means more distractions competing for your audience’s attention. Less screen space equals less retention.

The standard portrait format (4:5, 1080 x 1350 pixels) has been the go-to for years, and it’s still a solid choice. It’s taller than square, so it takes up more of the feed. The downside is that it still leaves a small band of unused space at the top and bottom of the screen, which limits how dominant your post looks while someone is scrolling.

The full portrait format (3:4, 1080 x 1440 pixels) is the one to aim for if you want maximum screen coverage. It’s taller than 4:5 and pushes right to the edges of most mobile screens, meaning less of the feed is visible around your post and more focus lands on your content. More screen means more attention, and more attention means better performance.

One important exception for ads

If you’re running paid ads rather than organic posts, stick to 4:5 (1080 x 1350). Instagram’s ad system does not currently support the 3:4 ratio for sponsored posts, so you’ll want to keep those at the standard portrait size to avoid any delivery issues.

The quick reference

Organic posts: use 3:4 (1080 x 1440) for maximum screen coverage. Paid ads: use 4:5 (1080 x 1350). Square (1:1, 1080 x 1080): avoid unless you have a specific reason for it.

Why it matters

The Instagram algorithm rewards content that keeps people engaged. If your post occupies more of the screen, a user has to scroll past more of your content to move on — and that extra fraction of a second of exposure adds up. It’s a small change with a meaningful impact on reach and performance over time.

If you’re putting time and budget into Instagram content and you’re not optimising your image sizes, you’re leaving easy wins on the table.

We help businesses get more from their social media and digital marketing. If you’d like a hand with your Instagram strategy or content, give us a call on 01793 239239 or drop us a line at [email protected]. We’d love to help.

Frequently asked questions

What is the best image size for an Instagram post?

For organic posts, the best image size is 3:4 at 1080 x 1440 pixels. This format takes up the most screen space on a mobile feed, which means more attention and less competition from surrounding content. For paid ads, use 4:5 at 1080 x 1350 pixels, as Instagram’s ad system does not currently support 3:4 for sponsored posts.

What’s the difference between 4:5 and 3:4 on Instagram?

Both are portrait formats, but 3:4 (1080 x 1440px) is taller than 4:5 (1080 x 1350px). The taller format fills more of the screen when someone is scrolling, leaving less of the surrounding feed visible. This gives your post greater visual dominance and typically results in better engagement.

Is a square (1:1) image OK for Instagram?

Square posts at 1080 x 1080 pixels are technically fine, but they’re the least effective format for screen coverage. Because they’re smaller, there’s more unused space around the post and more competing content visible at the same time. Unless you have a specific creative or branding reason to use square, portrait formats will generally perform better.

Can I use 3:4 images for Instagram ads?

Not currently. Instagram’s advertising system does not support the 3:4 aspect ratio for sponsored posts. If you’re running paid ads, stick to 4:5 (1080 x 1350 pixels) to avoid display or delivery issues.

Does image size affect the Instagram algorithm?

Not directly, but it affects engagement — and engagement does influence the algorithm. A taller image occupies more screen space, which means users spend longer viewing your content as they scroll past it. That increased dwell time signals to Instagram that your post is worth showing to more people.

What resolution should Instagram images be?

Instagram recommends uploading images at 1080 pixels wide. For the three main formats, that means 1080 x 1080 for square (1:1), 1080 x 1350 for standard portrait (4:5), and 1080 x 1440 for full portrait (3:4). Uploading at the correct resolution avoids Instagram recompressing your image and losing quality.