Aspect Ratio Calculator

This free aspect ratio calculator does three jobs. It tells you the ratio of any size, so 1920 by 1080 comes back as 16:9. It resizes without squashing when you fill in one new measurement. And it shows exactly how many pixels a ratio change costs, whether you crop or add bars.

Your size, in pixels

That is 16:9

Widescreen HD

New size: fill in one, we work out the other

Use it in code

CSSaspect-ratio: 16 / 9;

Tailwindaspect-video

What does this aspect ratio calculator do?

It answers the three questions that actually come up, not just the easy one.

What ratio is this? Type 1920 by 1080 and it comes back as 16:9, Widescreen HD, with the exact simplified fraction underneath.
What is the other measurement? Fill in one new number and the other follows, so nothing gets squashed.
What does changing the ratio cost me? This is the part other calculators skip. Pick a target and see, in pixels and in percent, what a crop throws away and what bars would be added instead.

On top of that: platform presets with the exact size for Reels, TikTok, YouTube, Pinterest and more, each carrying the date it was last checked, and ready-made commands for CSS, Tailwind, FFmpeg and ImageMagick.

What is an aspect ratio?

An aspect ratio is the shape of a frame, written as width against height. It says nothing about size.

That is the part that confuses people. 320×180, 1920×1080 and 3840×2160 are all 16:9. They are wildly different file sizes and wildly different resolutions, but they are the same shape, so an image made for one fits any of them without distortion.

Ratios are written as a simplified fraction, which is why 1920×1080 reduces to 16:9 and not 1920:1080. Some are written against 1 instead, like the 2.39:1 used in anamorphic cinema.

How much do you lose changing ratio?

A lot more than most people expect, and this is the number nobody publishes.

From	To	What a crop keeps	What it throws away
16:9 (1920×1080)	9:16	608×1080	68% of the picture
4:3 (1600×1200)	16:9	1600×900	25%
4:3 (4000×3000)	9:16	1688×3000	58%
1:1 (1080×1080)	9:16	608×1080	44%

The 16:9 to 9:16 row is why a horizontal video rarely survives the trip to Reels or TikTok by cropping alone. Two thirds of the frame disappears, and whatever was at the edges goes with it. That is the case for reframing shot by shot, or for bars.

Crop or bars? The honest trade

Crop to fill scales your image until it covers the whole target frame, then trims what hangs over the edges. Nothing is empty, everything fits, and you lose picture.

Fit with bars scales your image until it all fits inside the target frame, then fills the leftover space. Nothing is lost, and you gain empty space.

There is no third option. Either you throw away picture or you add space: the two are the whole set.

Practical guidance:

Crop when the subject sits near the centre and the edges are scenery. Social platforms favour content that fills the screen, so crop when you can.
Bars when losing any of the frame breaks the shot, when a caption or logo sits near an edge, or when the original composition matters.
Blurred fill is the middle ground most editors offer: the same geometry as bars, but the empty space holds a blurred, zoomed copy of your own frame instead of black. The maths on this page is identical either way.

Letterbox and pillarbox, told apart

Both are bars. The difference is which edge they land on, and it depends only on which shape is wider.

Letterbox: bars on the top and bottom. Happens when your picture is wider than the frame, like a 16:9 film on an old 4:3 television.
Pillarbox: bars on the left and right. Happens when your picture is narrower than the frame, like a vertical phone clip played on a widescreen TV.

The calculator names the one you will get, and gives the bar thickness in pixels, so you know before you export.

The ratios worth knowing

16:9 Widescreen HD. YouTube, TV, most monitors, nearly all video.
9:16 Vertical. Stories, Reels, TikTok, Shorts.
4:5 Portrait. The Instagram feed default since the grid change in early 2026, and the tallest shape the main feeds accept.
1:1 Square. Profile images, some feed posts, product shots.
4:3 The old television and the old compact camera. Still common in tablets and in some sensors.
3:2 35mm film, and therefore most DSLR and mirrorless cameras.
2:3 The same shape turned vertical. The standard Pinterest Pin.
1.91:1 The link preview shape, the reason Open Graph images are 1200×630.
2.39:1 Anamorphic cinema. The widest thing you will meet in practice.

Why 2560×1080 is not really 21:9

Because 21:9 is a marketing name, not a measurement.

Do the arithmetic on a 2560×1080 ultrawide monitor and you get 64:27, which is about 2.37:1. True 21:9 would be 2.33:1. The industry rounded it to a friendlier pair of numbers and the label stuck.

This tool shows both, on purpose: the name people use, and the exact fraction underneath. Same story for 1.91:1 link previews, which are really 40:21.

Platform sizes go stale, and that matters

Any size guide without a date on it should be treated with suspicion. Instagram moved its feed default to 4:5 in early 2026. Guides written in 2024 still say 1:1, and they are confidently wrong.

So every preset here carries the month it was last checked, printed next to the buttons rather than buried in a footer. When we recheck them, that date moves.

One useful piece of insurance: ratios age far more slowly than pixel recommendations. Reels has been 9:16 since it launched, even as the recommended resolution moved. If you build to the ratio, a changed recommendation costs you a resize, not a reshoot.

What this tool does not do

It does not edit your image or video. It calculates and hands you the command. There is no upload, no file processing, and no queue.
It does not reframe with AI. Following a face across a shot so a 16:9 clip survives as 9:16 is a genuinely different product, and the tools that do it charge for it. We do the geometry, honestly, and tell you what a plain centre crop would cost.
It does not guess what matters in your picture. The crop is centred, because that is the only assumption we can make without seeing the file.
It is not a live guarantee of platform sizes. It is a dated snapshot, which is the most any page can honestly claim.

Who uses this

Social media managers turning one shoot into feed, Stories and Shorts without three separate exports.
Video editors deciding, before the render, whether a clip can be cropped or has to be reframed.
Photographers printing to a standard frame size and needing to know what the crop eats.
Front-end developers reserving space with aspect-ratio so images do not shift the layout while loading.
Anyone who has ever exported something and watched the platform cut the top of a head off.

Frequently asked questions

What aspect ratio is 1920x1080?

It is 16:9, the widescreen HD standard. Aspect ratio describes shape, not size, so it stays 16:9 whether the image is 320 by 180 or 3840 by 2160. Type any two numbers here and the ratio is simplified for you, along with the name it is known by.

How much of my image is lost going from 16:9 to 9:16?

Roughly 68 percent of a 16:9 frame disappears when you crop it to 9:16. A 1920 by 1080 video becomes 608 by 1080, losing 656 pixels from each side. That is why a horizontal shot rarely survives the move to Reels without being reframed rather than simply cropped.

What is the difference between letterbox and pillarbox?

Letterboxing adds bars on the top and bottom, which happens when your picture is wider than the frame. Pillarboxing adds bars on the left and right, which happens when it is narrower. Both keep the whole picture, unlike cropping, and this calculator tells you which one you will get.

What size should an Instagram post be?

The portrait feed post is 1080 by 1350 pixels, a 4:5 ratio, which became the default after the grid change in early 2026. Stories and Reels are 1080 by 1920, a 9:16 ratio. Both presets are here, with the date they were last checked shown on the page.

What size is a YouTube thumbnail?

It is 1280 by 720 pixels, which is 16:9, the same shape as the video itself. Shorts use 1080 by 1920 instead, a 9:16 vertical frame. Pick the preset here and you also see what a crop from your current size would cost in pixels.

Should I crop or add bars?

Crop when the subject sits near the centre and the edges carry nothing important. Add bars when losing any of the frame would break the shot, or when a caption sits near an edge. Social platforms generally favour full-frame content, so cropping tends to perform better where it is possible.

Why is 2560x1080 called 21:9 when the maths says 64:27?

Because 21:9 is a marketing label, not the exact fraction. Ultrawide monitors sold as 21:9 are usually 64:27, which is about 2.37 to 1 rather than 2.33. This calculator shows both: the name the industry uses, and the exact simplified fraction underneath it.

Does this tool resize my actual image?

No. It calculates and hands you the numbers plus a ready-made command for FFmpeg or ImageMagick. Nothing is uploaded and no file is edited, because the job here is working out what to do before you do it, not doing it for you.

How do I keep an aspect ratio in CSS?

Use the aspect-ratio property, for example aspect-ratio: 16 / 9, and the browser reserves the right height for the width available. This page gives you that line ready to copy, plus the matching Tailwind class, which also prevents the layout shift that hurts your Core Web Vitals.

Are these platform sizes still current?

Each set carries the month it was last checked, shown next to the presets on the page. Platforms change these regularly, so any size guide without a date should be treated with suspicion. Ratios move far less often than exact pixel recommendations do.