Aspect Ratio Calculator

Common resolutions by aspect ratio

Every height below is computed from the width and the exact ratio, and the "exact ratio" column is the true simplified fraction of the pixels. That matters for ultrawides: monitors sold as 21:9 actually ship pixel grids like 64:27 or 43:18, which is why cropping math on them never comes out to a clean 21:9.

Give it one side, get the other

Feed the calculator an aspect ratio plus a width or a height, and it hands back the missing dimension. That’s the whole job. Video editors, UI designers, and photographers hit this math all day.

Seven presets cover the ratios you’ll actually type:

• 16:9 drives Full HD, 4K, and nearly every YouTube upload.
• 4:3 is the old TV and slide-deck shape, still standard on projectors.
• 1:1 is the square Instagram grid tile and most avatars.
• 9:16 is vertical video: Reels, TikTok, Stories.
• 21:9 covers ultrawide monitors and cinematic crops.
• 3:2 is the native frame on most DSLRs and 4x6 prints.
• 5:4 shows up on older 1280x1024 monitors and some photo sizes.

Got something odd? Type any two integers into the ratio fields and the tool simplifies them with a GCD, so 1920:1080 collapses to 16:9 in the corner.

Reading the resolution tables

The tables above list exact pixel resolutions for each family, with the true simplified ratio sitting next to the marketing name. That last column matters more than people expect. A monitor sold as “21:9” is almost never 21:9 in pixels: 3440x1440 is exactly 43:18, 2560x1080 is 64:27, and 3840x1600 is 12:5. The marketing rounds. The pixels don’t.

Same story one row up. What resolution is 16:9 at 1600 pixels wide? It’s 900 tall, so 1600x900, which is why that size sits in the 16:9 block. Skimming the tables beats recomputing the common cases by hand every time.

Crop, scale, or letterbox

Say you’ve got a 1920x1200 image, which is 16:10 (exactly 8:5), and a slot that wants 16:9. Three ways out:

• Crop: shave 120 pixels off the height down to 1920x1080. Fast, but you lose the top and bottom edges.
• Letterbox: scale the whole frame to 1920x1080 and pad with bars so nothing gets cut.
• Pillarbox: match the height and let the width fall where it wants, which changes the ratio.

Which one’s right comes down to whether losing edge content or adding bars hurts less. Upload targets usually dictate a ratio, so match it or accept the bars.

Frequently asked questions

What resolution is 16:9 at 1600 pixels wide?

900 pixels tall, giving you 1600x900. Multiply the width by 9 and divide by 16. It’s a genuine 16:9 size and lives in the top table above.

Is 1366x768 really 16:9?

No. It works out to exactly 683:384, a hair wider than 16:9 (a true 16:9 at 768 tall would be 1365.33 wide, which isn’t a whole pixel). Laptop panels settled on 1366x768 for manufacturing reasons, so the “16:9” label is a rounding, not the real ratio.

How do I convert 4:3 to 16:9?

Keep the height and grow the width by a factor of 4/3, or keep the width and shrink the height. A 1024x768 (4:3) frame would need to be 1365.33 wide for true 16:9, which lands between pixels, so you either crop the top and bottom or add pillarbox bars on the sides. There’s no lossless exact conversion between the two shapes.

Why are some ratios written as decimals?

Cinema specs are often irrational. CinemaScope is 2.39:1 (sometimes printed 2.40:1), and “21:9” monitors are really 64:27 or 43:18 depending on the panel. For pixel work, the integer approximation in the tables is close enough.

What aspect ratio works best for a portfolio grid?

1:1 is the safe pick, because square thumbnails line up cleanly on every screen size. Use 16:9 if you want cinematic hero images, but stay consistent so the grid doesn’t look ragged.

How do I find my screen’s aspect ratio?

Divide the pixel width by the height. 1920/1080 is 1.777, which is 16:9; 2560/1080 is 2.37, which wears the “21:9” label but is really 64:27. Most consumer monitors are 16:9, and productivity or gaming panels drift ultrawide.