Aspect Ratio Calculator
Find a missing width or height that keeps the original aspect ratio, and see the simplified ratio.
Resize without distortion
The Aspect Ratio Calculator finds the width or height you need to resize an image or video while keeping its original proportions. Enter the original dimensions, then type either a new width or a new height — the tool fills in the other so nothing gets stretched or squashed. It also shows the simplified aspect ratio.
What is aspect ratio?
Aspect ratio is the relationship between width and height, written like 16:9 or 4:3. It's what keeps an image looking correct: change one dimension without adjusting the other proportionally, and the image distorts. Knowing the ratio lets you resize confidently for any target size.
How to use it
- Enter the original width and height.
- Type a new width or a new height (leave the other blank).
- The matching dimension is calculated to preserve the ratio.
Common aspect ratios
| Ratio | Used for |
|---|---|
| 16:9 | Video, widescreen displays, YouTube |
| 4:3 | Older displays, some photos |
| 1:1 | Square — Instagram posts, avatars |
| 9:16 | Vertical video — Stories, Reels, TikTok |
Where it helps
- Resizing images for the web without distortion.
- Video — fitting content to 16:9 or 9:16 frames.
- Design — scaling mockups and assets proportionally.
- Print — keeping photos in proportion at new sizes.
Tips
If you only know the target width (say, a 600px content column), enter it and let the tool compute the height that keeps your image's ratio. The simplified ratio it shows (like 16:9) is handy for choosing standard frame sizes and confirming two assets share the same proportions.
Private and free
All calculations run in your browser — nothing is uploaded. The tool is completely free with no sign-up.
Frequently asked questions
How do I keep the aspect ratio when resizing?
Enter the original size, then set one new dimension. The tool calculates the other so the proportions stay the same.
What is a 16:9 ratio?
A widescreen ratio where width is 16 units for every 9 units of height — standard for video and modern displays.
Does it show the simplified ratio?
Yes. It reduces your original dimensions to their simplest ratio, like 1920×1080 to 16:9.
Is it free?
Yes, completely free with no sign-up, running entirely in your browser.