Aspect Ratio Calculator
Resize without distortion. Enter your original width and height, type either new dimension, and the other one is filled in for you — plus the simplified ratio, the closest broadcast standard, megapixels, and the exact letterbox size for fitting into any target frame.
- ✓ Ratio lock both ways
- ✓ Fit & fill calculations
- ✓ Social platform presets
- ✓ Live shape preview
- ✓ Closest standard ratio
Original size
Common ratios
Platform presets
New size — type either box
Fit into a target frame
The maths behind an aspect ratio
Aspect ratio is just width divided by height, reduced to its smallest whole numbers. 1920 ÷ 1080 gives 1.778, and dividing both sides by their greatest common divisor of 120 gives 16:9. Everything else on this page is that one idea applied in different directions.
ratio = width ÷ height1920:1080 ÷ 120 = 16:9newH = newW × (h ÷ w)newW = newH × (w ÷ h)scale = min(frameW ÷ w, frameH ÷ h)scale = max(frameW ÷ w, frameH ÷ h)Why this beats the usual four-box calculator
Locks in both directions
Type a width and the height follows. Type a height and the width follows. No deciding in advance which one you are solving for.
Contain and cover, calculated
Fitting a 16:9 frame into a 1:1 post is where people guess. You get the exact contained size, the exact cover size and the crop or bar thickness in pixels.
Platform presets built in
YouTube thumbnails, Reels, Shorts, Pinterest pins, LinkedIn banners. One tap loads the real dimensions instead of a search.
Closest standard ratio
Odd crops like 1512×982 do not reduce to anything readable. You get the ugly true ratio and the nearest recognised standard side by side.
Live shape preview
The proportion is drawn as you type, which catches a transposed width and height instantly — the single most common resizing error.
Instant and private
Pure arithmetic in your browser. No uploads, no account, no external requests, nothing stored.
How to use the aspect ratio calculator
- Enter your original size
Put in the pixel dimensions you already have, or tap a common ratio or platform preset to load them.
- Type one new dimension
With the ratio locked, entering a new width fills in the height and vice versa. Unlock it if you deliberately want to change the proportion.
- Check the shape preview
If the drawn rectangle looks wrong, your width and height are the wrong way round. Tap the swap button rather than retyping.
- Set the target frame
Enter the frame you need to land in and read the contain size, the cover size and the exact bars or crop each one produces.
Common aspect ratios and where they are used
| Ratio | Decimal | Typical resolution | Used for |
|---|---|---|---|
| 16:9 | 1.778 | 1920 × 1080 | HDTV, YouTube, most monitors |
| 4:3 | 1.333 | 1024 × 768 | Legacy displays, iPad, slides |
| 3:2 | 1.500 | 6000 × 4000 | DSLR and mirrorless photos |
| 1:1 | 1.000 | 1080 × 1080 | Square social posts, avatars |
| 4:5 | 0.800 | 1080 × 1350 | Instagram portrait posts |
| 9:16 | 0.563 | 1080 × 1920 | Reels, Shorts, TikTok, Stories |
| 2:3 | 0.667 | 1000 × 1500 | Pinterest pins, book covers |
| 5:4 | 1.250 | 1280 × 1024 | Older LCD monitors, large format |
| 21:9 | 2.370 | 3440 × 1440 | Ultrawide monitors |
| 1.85:1 | 1.850 | 1998 × 1080 | Cinema flat widescreen |
| 2.39:1 | 2.390 | 2048 × 858 | Anamorphic scope, film |
| 3:1 | 3.000 | 1500 × 500 | X / Twitter header |
21:9 is a marketing name rather than exact maths. A 3440 × 1440 panel is really 43:18, and 2560 × 1080 is 64:27, which is why the calculator shows both the true reduced ratio and the standard it is closest to.
Social media image sizes
Current recommended upload dimensions. Platforms re-compress everything, so uploading at these sizes rather than larger keeps the most detail.
| Placement | Size | Ratio |
|---|---|---|
| YouTube video | 1920 × 1080 | 16:9 |
| YouTube thumbnail | 1280 × 720 | 16:9 |
| YouTube Shorts | 1080 × 1920 | 9:16 |
| Instagram square | 1080 × 1080 | 1:1 |
| Instagram portrait | 1080 × 1350 | 4:5 |
| Instagram Reels | 1080 × 1920 | 9:16 |
| Placement | Size | Ratio |
|---|---|---|
| TikTok video | 1080 × 1920 | 9:16 |
| X / Twitter post | 1600 × 900 | 16:9 |
| X / Twitter header | 1500 × 500 | 3:1 |
| LinkedIn banner | 1584 × 396 | 4:1 |
| Facebook cover | 1640 × 856 | ~1.91:1 |
| Pinterest pin | 1000 × 1500 | 2:3 |
What getting the ratio right saves you
- ✓No stretched faces. Forcing a 16:9 image into a 1:1 slot without a ratio-preserving scale is what produces the squashed look everyone recognises.
- ✓No auto-crop surprises. Platforms crop from the centre. Knowing the cover crop in advance tells you how much headroom to leave when shooting.
- ✓Cleaner CSS. Knowing the true ratio lets you set a fixed
aspect-ratioand stop layout shift before it starts.
- ✓Sharper uploads. Uploading at the platform’s native size avoids a second round of downscaling and re-compression.
- ✓Predictable video exports. Matching your timeline ratio to the delivery ratio prevents surprise letterboxing on export.
- ✓Faster batch work. One scale factor applied to a whole folder keeps every asset consistent.
Aspect ratio FAQs
How do I calculate aspect ratio?
Divide the width by the height, then reduce both numbers by their greatest common divisor. For 1920 × 1080 the GCD is 120, so 1920:1080 becomes 16:9. The decimal form, 1.778, is often more useful in code than the colon form.
What is the aspect ratio of 1920x1080?
16:9, decimal 1.778. It is the standard for HD and Full HD video, almost all modern televisions and monitors, and default YouTube uploads. 1280 × 720 and 3840 × 2160 are the same 16:9 shape at different resolutions.
How do I resize an image without distorting it?
Multiply rather than pick both numbers independently. To reach a new width, the new height is newWidth × (originalHeight ÷ originalWidth). Going from 1920 × 1080 to 1280 wide gives 1280 × 0.5625, which is 720. Keeping the ratio locked in this calculator does that for you.
What is the difference between 16:9 and 21:9?
16:9 is 1.778 wide for every unit of height, 21:9 is roughly 2.37. A 21:9 ultrawide shows about a third more horizontal image than a 16:9 screen of the same height. 21:9 is an approximate label: 3440 × 1440 is exactly 43:18 and 2560 × 1080 is exactly 64:27.
What aspect ratio should I use for Instagram?
4:5 portrait at 1080 × 1350 takes the most feed space and generally performs best for still posts. Use 1:1 at 1080 × 1080 for a square grid look and 9:16 at 1080 × 1920 for Reels and Stories. Anything taller than 4:5 gets cropped in the feed.
What does 4:3 mean?
Four units of width for every three of height, a decimal ratio of 1.333. It was the standard for pre-HD television and computer monitors and survives in tablets, many camera sensors in photo mode and default presentation slides.
How do I convert a 16:9 video to 9:16 for Shorts or Reels?
You have to choose between contain and cover. Contain scales the whole frame to 1080 wide, giving 1080 × 608 with large bars above and below. Cover scales until the frame is filled, giving 3413 × 1920 and cropping about 68% of the width away. Most vertical edits use cover with the subject re-framed, or contain with the bars filled by a blurred copy.
What is a 2.39:1 cinematic aspect ratio?
The modern anamorphic scope standard, used for most theatrical widescreen releases. On a 1080-pixel-tall timeline it works out to roughly 2581 × 1080, and on a 16:9 delivery frame it appears with black bars occupying about 25% of the height.
Resize it right the first time
Enter your dimensions, lock the ratio and get the exact pixel sizes for every frame you need to hit.
Calculate my ratio →