Aspect ratio calculator for ads and social posts

How the ratio is worked out

An aspect ratio is the width divided by the height. To write it as two whole numbers, divide both sides by the largest number that goes into each of them. A few worked examples:

• 1080 × 1350: both divide by 270, which gives 4:5. As a decimal, 1080 ÷ 1350 = 0.8.
• 1920 × 1080: both divide by 120, which gives 16:9, or 1.7778.
• 1200 × 628: the largest common factor is only 4, so the exact ratio is 300:157. As a decimal it is 1.9108, which is why everyone calls it 1.91:1.

Going the other way is one multiplication. If you know the ratio and one side, the missing height is width ÷ ratio, and the missing width is height × ratio. For 9:16 at 1080 wide: 1080 ÷ (9 ÷ 16) = 1920. When the answer is not a whole number, the calculator rounds to the nearest pixel and shows you the exact value, so you know how far off the rounding is.

Recommended ratio and size for each placement

This table lists only what each platform states on its own spec page, and each row links to that page. Where a platform gives a ratio and no recommended pixel size, the table says so rather than filling the gap with a guess. Most of these are ad placements, because that is where the platforms publish exact numbers.

Two details from those pages are worth knowing. Meta allows a small tolerance on the ratio: its guide lists 1% for the Instagram Feed and Stories image specs and 3% for the Facebook Feed image spec, so a 1440 × 1790 image still counts as 4:5 on Facebook Feed (it is 0.6% off). And Pinterest warns that Pins with an aspect ratio greater than 2:3 might get cut off in people’s feeds, so a taller Pin is a gamble rather than an advantage.

Crop, or recompose?

A centre crop keeps the middle and throws away the edges. The preview above shows exactly how much survives. A 1920 × 1080 frame cropped to 9:16 keeps a 608 × 1080 strip, which is about 32% of the picture. Cropped to 4:5 it keeps 864 × 1080, or 45%. If your product or headline sits near an edge, a crop will cut it.

For vertical placements, the crop is only half the problem. Stories, Reels, TikTok and Shorts also paint their own buttons and captions over the frame. Once your image is 9:16, check it in the safe zone checker to see what those overlays cover. And if you are building a swipeable post from one wide image, the carousel splitter cuts it into equal slides at 1:1, 4:5, 9:16 or 1.91:1.

What this tool does not do

It does not resize or export your image, and it does not upload it anywhere. The crop preview is a quick look, drawn at a small size on this page. It also does not read video files. And the placement table is only as current as the platforms’ own spec pages, which change: when a number matters for a launch, click through to the source link before you export.

If you would rather not resize by hand

Hermoso is marketing on autopilot: it researches the ads already working in your market, makes on-brand image and video ads, schedules the posts and runs paid campaigns on your own ad accounts. Point it at an existing static ad and ask for other sizes, and the ad is laid out again for each canvas rather than cropped: things move, the background extends and the copy stays word for word. It can also reframe a video to another aspect ratio. It works in the web app, or inside Claude, ChatGPT and Cursor through its MCP server.

Frequently asked questions

How do I calculate an aspect ratio?

Divide the width and the height by their largest common factor. 1080 × 1350 divides by 270 to give 4:5. For the decimal form, divide width by height: 1080 ÷ 1350 = 0.8.

How do I find the height for a given width and ratio?

Divide the width by the ratio. For 9:16 at 1080 pixels wide, 1080 ÷ (9 ÷ 16) = 1920, so the image is 1080 × 1920. For the width from a height, multiply the height by the ratio.

What size should a Facebook or Instagram feed ad be?

Meta's Ads Guide recommends 4:5 at 1440 × 1800 pixels for Facebook Feed and Instagram Feed image ads, and 9:16 at 1440 × 2560 for Stories and Instagram Reels.

Is 1200 × 628 really 1.91:1?

Almost. The exact ratio is 300:157, which is 1.9108 as a decimal, so it rounds to 1.91:1. LinkedIn and X both list 1200 × 628 as their recommended landscape image ad size.

Does cropping to 9:16 cut off much of a landscape image?

Yes. A centre crop of 1920 × 1080 to 9:16 keeps a 608 × 1080 strip, about 32% of the picture. If the subject is not in the middle, recompose rather than crop.

Is my image uploaded?

No. The image is read by your browser and drawn on this page. There is no network request carrying it, and nothing is stored, so reloading the page clears it.