How do I calculate an aspect ratio?

Divide the width and the height by their greatest common divisor. 1920 and 1080 share 120, which gives 16:9. This page does that as you type, and falls back to a decimal when the pair does not reduce to numbers anybody would recognise.

What does 16:9 actually mean?

It means the picture is sixteen units wide for every nine units tall, whatever a unit happens to be. That is why 1920x1080, 1280x720 and 3840x2160 are all 16:9: they differ in resolution, not in shape.

Why does my ratio show as about 1.91:1 instead of whole numbers?

Because it genuinely is not whole numbers. A 1080x566 frame reduces to 540:283, which is accurate and unreadable, so the honest answer is the decimal with the recognised name beside it rather than a tidy fraction that nobody uses.

Why is the height one pixel off what I expected?

Pixels are whole, so a solved side is rounded. A 16:9 frame at 1000 wide is 562.5 tall in theory and 563 in practice, which divides back to 1.7762 rather than 1.7778. It is still the same shape, and the calculator recognises it as one.

Yes. This tool does its work in your browser, so whatever you type, paste or upload stays on your device. Nothing is sent to our servers, which is also why it keeps working if you go offline after the page has loaded.

Yes. Every tool here is free with no account, no credit card and no usage cap. They exist so that the people who need our scheduling product find us, which only works if the tools are genuinely useful on their own.

Do I need an account?

No. Open the page and use it. An account is only for OctoSpark itself, where you plan, schedule and publish a whole calendar rather than fixing one post at a time.

Can I use the output commercially?

Yes. Anything you produce here is yours, including for client and commercial work. We claim no rights over it and we do not watermark it.

OctoSpark

Free tool — runs in your browser

Aspect ratio calculator

Enter any two of width, height or ratio and get the third. It reduces any pixel pair to its simplest shape and names that shape when it is a known one.

Width and height

Width in pixels

Height in pixels

With the ratio unlocked, each side is yours to set and the shape below follows.

Aspect ratio

16:9

A 16:9 frame.

How this is worked out

Reduced by their greatest common divisor: 16:9
Width divided by height: 1.7778
Both terms are small enough to print as a ratio.

Lock to a named shape

Any platform shapes

Square (1:1)

The only shape that reads the same in a grid, a circle and a feed, which is why avatars and carousels live here.

10 image resizer presets match this shape.

Tall feed post (4:5)

A fifth taller than a square, and the most vertical space a feed post is usually allowed.

1 image resizer preset match this shape.

Portrait photo (3:4)

The shape a phone camera hands you before anything crops it, and the one photo posts keep.

1 image resizer preset match this shape.

Full screen vertical (9:16)

The entire phone display. Everything filmed for a story, a Reel, a Short or TikTok is this.

4 image resizer presets match this shape.

Widescreen (16:9)

Landscape video and thumbnails. Turn it on its side and you have the full screen vertical shape.

3 image resizer presets match this shape.

Link card and landscape post (1.91:1)

Slightly wider than widescreen, and the one common shape that refuses to reduce to small whole numbers.

5 image resizer presets match this shape.

How to calculate an aspect ratio

Two of the three numbers decide the third. Hand over a width and a height and you get the shape; lock a shape and one side, and the other side is solved for you. That second job is the one people actually arrive with, because it is the one arithmetic in your head gets wrong.

Type the width and the height you already have. The ratio below updates as you type, divided down as far as it will go by a greatest common divisor.
Lock the ratio once the shape is the one you want. From then on, changing the width moves the height with it and the shape stays put.
Or pick a named shape and keep your width. The height is solved against it, which is the fastest way to answer "how tall is 1440 pixels wide at 16:9".
Read the reduced form where there is one. 1920x1080 is 16:9, a shape people recognise, whereas 1.78:1 is a number nobody quotes.
Expect whole pixels. A 16:9 frame at 1000 wide comes out 563 tall rather than 562.5, so the result is a rounded neighbour of the exact shape and is still, sensibly, called 16:9.

What a ratio tells you that pixel sizes do not

A ratio is the part of a size that survives being resized. Two files can be a different number of pixels and the same shape, and only the shape decides what a platform crops away when it needs the picture to fit somewhere else.

Square, 1:1. The only shape that reads the same in a grid, a circle and a feed, which is why avatars and carousels live here. In our image resizer: Instagram square post at 1080x1080px, Instagram profile photo at 320x320px, Facebook profile photo at 170x170px, LinkedIn profile photo at 400x400px, and 6 more.
Tall feed post, 4:5. A fifth taller than a square, and the most vertical space a feed post is usually allowed. In our image resizer: Instagram portrait post at 1080x1350px.
Portrait photo, 3:4. The shape a phone camera hands you before anything crops it, and the one photo posts keep. In our image resizer: TikTok photo post at 1080x1440px.
Full screen vertical, 9:16. The entire phone display. Everything filmed for a story, a Reel, a Short or TikTok is this. In our image resizer: Instagram story / reel at 1080x1920px, Facebook story at 1080x1920px, TikTok video / story cover at 1080x1920px, YouTube shorts cover at 1080x1920px.
Widescreen, 16:9. Landscape video and thumbnails. Turn it on its side and you have the full screen vertical shape. In our image resizer: X (Twitter) post image at 1600x900px, YouTube video thumbnail at 1280x720px, YouTube channel banner at 2560x1440px.
Link card and landscape post, 1.91:1. Slightly wider than widescreen, and the one common shape that refuses to reduce to small whole numbers. In our image resizer: Instagram landscape post at 1080x566px, Facebook feed post at 1200x630px, Facebook event cover at 1200x628px, LinkedIn feed post at 1200x627px, and 1 more.

When a ratio refuses to reduce to whole numbers

Some shapes simply are not a ratio of small numbers, and the tidy answer is a lie. This calculator says so instead of inventing one, which is the difference between a number you can act on and a number that just looks precise.

A 1080x566 landscape post reduces to 540:283. Both terms are correct and neither is useful, so the answer given is "about 1.91:1" with the recognised name beside it.
Printing 191:100 would be worse than useless. It is a shape nobody documents, and it hides the fact that the real division is 1.9081 rather than 1.91.
Recognition uses a tolerance rather than an equals sign. A shape within half a percent of a named one is called by its name, and the exact division is still shown underneath.
That tolerance is what makes rounding survivable. Solve 16:9 at a width of 1000, get 1000x563, divide it back and you have 1.7762 rather than 1.7778: the same shape to any eye, and not the same number.
The cutoff for printing a ratio at all is a term of 20. Past that, a reduced pair stops being a shape you can picture and becomes a fraction you have to work out.

Where the calculator stops being the answer

Knowing the shape is the cheap half. Everything expensive about a picture happens after you have the number, and none of it is arithmetic that a browser can do for you.

A ratio says nothing about resolution. 160x90 and 3840x2160 are both 16:9, and only one of them survives a full screen.
Changing the ratio of an existing file means cropping or padding it. Deciding which half of a group photo to lose is a judgement, not a calculation.
Platforms crop from the centre by default, so a subject sitting off to one side is the first thing a shape change removes.
Video is not a still. Re-exporting a cover at a new shape does nothing about the bands around the footage playing behind it.
If the number you want is pixels rather than a shape, the image resizer exports to the exact sizes these pages quote, in your browser, with nothing uploaded.

The rest of the job

You just fixed one post. Now do the month.

The aspect ratio calculator solves one piece of one post. OctoSpark plans, writes and schedules the whole calendar across every network you use, publishes it for you, and reports what actually performed.

One calendar for every network
Schedule once, publish everywhere
Drafts written in your own voice
See what actually performed

Open the full sign-up page

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Frequently asked questions

How this tool works, what it cannot do, and what happens to what you put into it.

How do I calculate an aspect ratio?
Divide the width and the height by their greatest common divisor. 1920 and 1080 share 120, which gives 16:9. This page does that as you type, and falls back to a decimal when the pair does not reduce to numbers anybody would recognise.
What does 16:9 actually mean?
It means the picture is sixteen units wide for every nine units tall, whatever a unit happens to be. That is why 1920x1080, 1280x720 and 3840x2160 are all 16:9: they differ in resolution, not in shape.
Why does my ratio show as about 1.91:1 instead of whole numbers?
Because it genuinely is not whole numbers. A 1080x566 frame reduces to 540:283, which is accurate and unreadable, so the honest answer is the decimal with the recognised name beside it rather than a tidy fraction that nobody uses.
Why is the height one pixel off what I expected?
Pixels are whole, so a solved side is rounded. A 16:9 frame at 1000 wide is 562.5 tall in theory and 563 in practice, which divides back to 1.7762 rather than 1.7778. It is still the same shape, and the calculator recognises it as one.
Is my data private?
Yes. This tool does its work in your browser, so whatever you type, paste or upload stays on your device. Nothing is sent to our servers, which is also why it keeps working if you go offline after the page has loaded.
Is this really free?
Yes. Every tool here is free with no account, no credit card and no usage cap. They exist so that the people who need our scheduling product find us, which only works if the tools are genuinely useful on their own.
Do I need an account?
No. Open the page and use it. An account is only for OctoSpark itself, where you plan, schedule and publish a whole calendar rather than fixing one post at a time.
Can I use the output commercially?
Yes. Anything you produce here is yours, including for client and commercial work. We claim no rights over it and we do not watermark it.