Aspect Ratio Calculator
Keep pictures and videos in proportion when you resize them — and find the right size for each platform.
- Your data never leaves your device
- 100% free
- No sign-up
- Works offline after first load
How to calculate an aspect ratio
- Type a size or a ratio — or add a photo or video.
- Read the ratio, nearest standard and other sizes; pick a social media size.
- Copy the CSS or crop a picture to the ratio.
About Aspect Ratio Calculator
Calculate aspect ratios and missing sizes, read a photo or video’s ratio, see the closest standard ratio, use sizes for Instagram, YouTube, TikTok and more.
Everything works in your browser, so it is instant and private, and your settings are remembered on this device.
Good for
- Social media posts and videos
- Web design and responsive images
- Video editing and printing
Tip: Portrait 4:5 posts take up more of the Instagram feed than square or landscape ones.
Frequently asked questions
How do I keep the same ratio when resizing?
Type the new width (or height) — the other side is calculated so the ratio stays the same. Choose which side to keep when you change the ratio.
What ratio should I use for Instagram, TikTok and YouTube?
Instagram posts 1:1 or 4:5 (portrait gets more space), Stories, Reels, TikTok and Shorts 9:16, YouTube videos 16:9. All sizes are listed — click one to use it.
Can it find the ratio of my picture or video?
Yes — choose or drop a file. Its size and ratio are read in your browser, with the nearest standard ratio.
Can I crop a picture to a ratio?
Yes — after adding a picture, choose the ratio, move the crop and download the cropped image.
Is my photo or video uploaded?
No. When you read a file's ratio, it is opened in your browser and never leaves your device.