Aspect ratio calculator

An aspect ratio describes the relationship between an image or video's width and height, written as two numbers separated by a colon — for example 16:9 or 4:3. It tells you the shape of the frame, independent of its actual pixel size. A 1920×1080 video and a 1280×720 video are both 16:9 because both dimensions scale down to the same simplified ratio. Keeping the same ratio when you resize is what prevents distortion: stretch a 16:9 image into a 1:1 square without adjusting for the ratio and everything in it gets squashed or cropped unexpectedly.

The tool above uses the greatest common divisor (GCD) of your width and height to reduce the ratio to its simplest form automatically, the same way you'd simplify a fraction. Enter 2560×1440 and you'll see 16:9; enter 1000×1000 and you'll see 1:1. Use it as a quick ratio calculator whenever you just need to know what shape a pair of numbers describes, even if you never resize anything.

Under the hood, the calculator does two things at once. First, it computes the GCD of your original width and height using the Euclidean algorithm, then divides both numbers by it to get the smallest whole-number ratio that represents the same shape. Second, it treats that ratio as a lock: whenever you type a new width or a new height, the other field is recalculated on the fly using simple cross-multiplication — newHeight = newWidth × (originalHeight ÷ originalWidth) — and rounded to the nearest whole pixel.

Because the math runs client-side in plain JavaScript, there is no delay, no server round-trip, and no limit on how many times you can recalculate. You can also work backwards: enter a target width and height you already know you need, and read off the simplified ratio to understand what shape you're actually asking for.

To resize something proportionally, you only need to lock the ratio between width and height and then scale both together:

1. Enter your original size. Type your original width and height in the calculator above — this is the ratio it will preserve for every calculation that follows.
2. Type your target size. Enter your target width (or height) in the new-size fields. The other dimension is calculated for you automatically, rounded to the nearest whole pixel.
3. Copy the result. Use the copy buttons next to each field to grab the exact number without retyping it, then paste it into your design tool, video editor, or code.
4. Apply it. Use the calculated pair in your design tool, video editor, or CSS (width / height or aspect-ratio) so the output matches exactly.
5. Mind ratio changes. If you need to go the other direction — say, converting 1920x1080 to 9:16 for a vertical Reel — don't just rotate the numbers. A 9:16 crop of a 16:9 source usually means cropping the sides, not squashing the frame. Use the 9:16 preset to see the target size, then crop your source to fit.

Once you have the right dimensions, run the file through our image resizer to actually produce the resized file, then our image compressor to bring the file size down before you upload or publish it.

Every social and video platform expects a specific pixel size, and most of those sizes map to one of a handful of common ratios. Here is a quick reference so you don't have to look it up every time:

Beyond social platforms, a handful of classic ratios cover almost everything else you'll run into:

• 16:9 — 1920×1080. YouTube standard uploads, widescreen presentations, most desktop video, and modern TVs and monitors.
• 9:16 — 1080×1920. Instagram Reels, YouTube Shorts, TikTok, and other full-screen mobile video and Stories.
• 1:1 — 1080×1080. Square Instagram and Facebook feed posts, square video clips, and profile pictures.
• 4:5 — 1080×1350. Instagram portrait feed posts — taller than square, so it takes up more space in the mobile feed than a square post.
• 4:3 — 1600×1200. Older TV and camera formats, some presentation slides, and print photos.
• 21:9 — 2560×1080. Ultrawide monitors and cinematic video banners.
• 3:2 — 1620×1080. Classic DSLR photo ratio, common for print and photography.

Click any preset button in the calculator above to fill in both the original and new dimensions instantly — no need to remember or type these numbers by hand.

Not all ratios are created equal — each one carries a bit of history and a typical use case:

• 16:9 (widescreen) became the TV and monitor standard in the 2000s and is now the default for online video, replacing the boxier 4:3 of the CRT era.
• 9:16 (vertical) is simply 16:9 rotated 90 degrees, and it dominates short-form mobile video because people hold their phones upright far more often than they turn them sideways.
• 1:1 (square) was popularized by early Instagram, which only accepted square photos for years — it still works well for feed posts because it takes up consistent space regardless of device.
• 4:3 was the standard shape for television and film for most of the 20th century and still appears in some presentation software, older cameras, and printed photos.
• 21:9 (ultrawide) approximates cinematic widescreen film formats and is now common on ultrawide gaming monitors and cinematic-style video banners.
• 3:2 traces back to 35mm film photography and remains the native sensor ratio on most DSLR and mirrorless cameras.

• Design at the largest size you'll need, then scale down — scaling up a small image loses quality, but scaling down a large one keeps it sharp.
• When a platform requires a different ratio than your source, decide whether to crop (lose some content) or pad with a background (add letterboxing) rather than stretching the whole frame.
• For responsive web layouts, the CSS aspect-ratio property (e.g. 16 / 9) lets the browser maintain proportions automatically as the container resizes, without any JavaScript.
• Keep a note of your simplified ratio — many editing and design tools accept it directly as a crop preset, saving you from re-deriving it later.
• When shooting original video or photos, frame with the final ratio in mind. It is much easier to crop a 16:9 shot down to 9:16 if you left extra space around the subject than to try to recover detail that was never captured.
• Double-check platform specs before a big export; social apps update recommended sizes occasionally, and the cheat-sheet above covers the common current defaults.
• If you're exporting a whole batch of assets in different ratios for the same campaign, calculate each target size up front rather than resizing one and eyeballing the rest — small rounding differences add up across a set.

Distorted media is one of the fastest ways to make a brand look careless. A stretched logo, a squashed headshot, or a video with visible letterboxing signals that nobody checked the export before publishing. Beyond appearances, most platforms will automatically letterbox, crop, or reject uploads that don't match their expected ratio, which can mean your carefully framed shot gets an unexpected crop applied by the platform instead of by you.

Working out the correct proportional size ahead of time — rather than resizing by eye — means you control exactly what gets cropped or padded, and you can preview the composition before you export the final file. It also saves round-trips: instead of exporting, uploading, discovering the platform cropped your subject out of frame, and re-exporting, you can calculate the exact target size first and frame accordingly from the start.

This matters even more for teams that publish the same creative across multiple channels. A single hero image might need a 16:9 crop for a YouTube thumbnail, a 1:1 crop for an Instagram post, a 9:16 crop for a Story, and a 4:5 crop for a LinkedIn share — four different shapes from one source. Calculating each target size in advance, rather than resizing ad hoc in whatever tool is open, keeps every version consistent and avoids the drift that creeps in when four different people resize the same asset four different ways.

It's easy to conflate aspect ratio with resolution, but they answer different questions. Resolution is the raw pixel count — how much detail an image or video actually contains, such as 1920×1080 or 3840×2160 (4K). Aspect ratio is the shape those pixels form once you reduce the dimensions to their simplest proportion, such as 16:9. Two files can share a resolution but not a ratio only if one has been cropped or padded; more commonly, many different resolutions share the same ratio. 1280×720, 1920×1080, and 3840×2160 are all 16:9 — same shape, three very different levels of detail and file size.

This distinction matters when you're troubleshooting an export: if a video looks squashed after upload, the resolution is usually fine and the ratio is the problem, so check the ratio first rather than re-exporting at a higher resolution and getting the same distorted shape again.

Aspect ratio calculations aren't limited to screens. Print materials — business cards, posters, flyers, and packaging — follow the same proportional logic, just measured in inches or millimeters instead of pixels. A US Letter page (8.5×11 in) is roughly a 17:22 ratio, while ISO A-series paper (A4, A3, and so on) follows a fixed 1:√2 ratio so that folding a sheet in half always produces the next size down with the same proportions. If you're designing an image that needs to work both on screen and in a printed layout, calculate the print ratio first, then use this tool to find a pixel size at your target resolution (for example 300 DPI) that shares the exact same proportions, so nothing gets cropped when it moves from screen to paper.