Aspect Ratio Calculator

Enter your original width and height, then type a new width or height — the other is filled in automatically to keep the same aspect ratio. Or tap a preset (16:9, 9:16, 4:5, 1:1, 4:3) to set a shape instantly. It all runs in your browser; nothing is uploaded.

How to use the calculator

Put your current size in Original width and Original height — this sets the ratio you want to preserve. Then type the one dimension you know for the new size, either the width or the height, and the calculator fills in the other so the proportions stay identical. If you just need a standard shape, tap a preset and it sets the ratio for you, which you can then scale to any size.

A quick example: a 4000 × 3000 photo is 4:3. If you need it 1200 pixels wide for a blog, type 1200 into New width and the calculator returns 900 for the height — same shape, no distortion. Try to eyeball that and you will almost always stretch or squash the image.

Aspect ratio vs resolution — the difference

These two get confused constantly. Aspect ratio is the shape — the relationship between width and height, like 16:9 or 9:16. Resolution is the size in pixels, like 1920 × 1080. Two images can share a ratio (16:9) at very different resolutions (1280 × 720 and 3840 × 2160). This calculator locks the shape while you change the size, which is exactly what you want when a platform asks for a specific ratio but you also have a pixel target to hit.

Common aspect ratios and where they are used

Different platforms expect different shapes. The main ones creators meet:

• 9:16 — full-screen vertical: TikTok, Reels, Shorts and Stories (1080 × 1920).
• 16:9 — standard horizontal: YouTube video and thumbnails (1920 × 1080 or 1280 × 720).
• 4:5 — the tallest Instagram feed post (1080 × 1350), which takes the most screen space.
• 1:1 — square: profile pictures and a tidy feed grid (1080 × 1080).
• 3:1 — wide banners like the X header (1500 × 500).
• 4:3 — the classic ratio, still used for some displays, slides and prints.

Crop or pad — resizing between ratios

When your source and target ratios differ, something has to give. You either crop (fill the new frame and trim the overflow) or pad (keep the whole image and add bars to reach the shape). This calculator keeps a single ratio while you resize; when you actually need to change the shape of a photo, the social image resizer does the crop-or-pad for you. As a rule, crop for backgrounds and full-bleed video, pad when nothing in the frame can be lost.

Why aspect ratio matters

If you resize to the wrong ratio, the platform crops your image or adds black bars — and a letterboxed clip signals “made for somewhere else,” which costs watch time in the first second. Keeping the ratio fixed while you change the size avoids both: your whole frame is preserved and nothing important gets cut. It is the cheapest quality win in your workflow, and it compounds across every post.