Resize a 1920×1080 video to fit a 1280-pixel-wide player, crop a photo for a 4:5 Instagram post, or letterbox 21:9 footage onto a 16:9 screen — every one of these is an aspect-ratio problem. Get the math wrong and images stretch, faces distort, and videos grow black bars in the wrong places.
This calculator keeps width and height locked to a ratio: enter any three values and it solves the fourth, and it can reduce any resolution to its simplest ratio (1920×1080 → 16:9).
How to Use This Tool
- Enter the original width and height (or pick a preset like 16:9, 4:3, 21:9).
- Type the new width or the new height you need.
- The missing dimension is calculated to preserve the ratio exactly.
- Use the simplify mode to discover the ratio of any resolution.
Frequently Asked Questions
What are the most common aspect ratios today?
16:9 dominates video (YouTube, TV, most phones in landscape); 4:3 is classic photography and older displays; 1:1 and 4:5 rule Instagram; 9:16 is vertical video for Stories, Reels, and TikTok; cinema uses 21:9 and wider.
Why do my images look stretched after resizing?
Because the new dimensions do not share the original ratio, and the software scaled without cropping. Either compute one dimension from the other (what this tool does) or crop to the target ratio before scaling.
How do I convert a resolution to its ratio?
Divide both numbers by their greatest common divisor: 1920 and 1080 share 120, giving 16:9. Odd-looking results like 683:384 usually mean the resolution was already slightly cropped from a standard ratio.