Aspect Ratio Calculator: Scale Images and Video Without Distortion
How to find equivalent dimensions when resizing images, videos, or UI elements — with examples for 16:9, 4:3, and other common ratios.
Resizing an image sounds simple until it isn’t. You have a 1920×1080 banner and need it to fit a 400px-wide column. Do you just halve everything? Not quite — without the right calculation, you end up with something stretched, squashed, or cropped wrong.
The Aspect Ratio Calculator handles this. Enter your original dimensions, see the simplified ratio, then enter one new dimension and get the other.
What an aspect ratio actually is
An aspect ratio is the width-to-height relationship of any rectangle, simplified to its smallest whole-number form. 1920×1080 reduces to 16:9. 2560×1440 is also 16:9 — same ratio, different resolution. 800×600 reduces to 4:3.
The simplification uses the greatest common divisor (GCD). For 1920 and 1080, the GCD is 120. Dividing both by 120 gives 16:9.
Not every pair of dimensions yields a clean named ratio. 1366×768 — the old budget-laptop standard — reduces to 683:384. No marketing department would use that name, but for scaling purposes it works exactly the same way.
Common ratios and where you find them
16:9 is everywhere: HD and 4K monitors, YouTube, Vimeo, most smart TVs, PowerPoint slides. If you’re making a video thumbnail or a widescreen banner, this is probably your target.
4:3 is the older television standard. Many presentation apps still default to it when you choose a “classic” layout. A lot of digital cameras also shoot stills in 4:3.
1:1 squares show up in Instagram feed posts, profile pictures, and some print formats like CD covers.
9:16 is the vertical flip of 16:9 — TikTok, Instagram Reels, Instagram Stories, YouTube Shorts. It’s easy to forget when cropping a landscape video that the proportions work out very differently in portrait.
21:9 ultrawide is less common but gaining ground in gaming and video editing. Some cinematic films are mastered close to this ratio.
How to use the calculator
Enter 1920 in the width field and 1080 in the height field. The ratio shows 16:9 immediately. Now say you want a version that’s 800px wide. Type 800 in the “new width” field — you get 450. Correct. Enter 1280 and you get 720. Both are valid 16:9 dimensions.
The same logic runs in reverse. Enter 400 in the new height field and the matching width for a 16:9 source comes out as 711. The result is rounded to the nearest whole pixel, which is close enough for every practical use case.
The math, if you want it
New height = (new width × original height) ÷ original width.
New width = (new height × original width) ÷ original height.
That’s the whole thing. The Aspect Ratio Calculator runs this in the browser — no data goes anywhere.
What it won’t do
Cropping is a different problem. If you have a 4:3 image and need a 16:9 output, scaling alone won’t work. You’ll either add letterbox bars, crop the sides, or stretch — all three are valid choices depending on context. The calculator tells you what dimensions to target; what to do with the leftover pixels is a decision you make in your image or video editor.
Enter your dimensions into the Aspect Ratio Calculator and get the scaled size right away.