Aspect Ratio Calculator — Scale Dimensions Online Free
Original dimensions
W
× H
Aspect ratio
—
Scale to new dimensions
Enter new width → get height
→ Height: — px
Enter new height → get width
→ Width: — px
Enter the original width and height to see the simplified aspect ratio (16:9, 4:3, 1:1, and so on). Then enter a new width to get the matching height, or a new height to get the matching width — useful for resizing images, video frames, or UI containers without distortion. Common format presets are included.
How it works
- 1 Enter original dimensions Type the width and height of your image, video, or container. Or click one of the preset buttons (16:9, 4:3, 1:1, 9:16, 21:9) to fill in common values.
- 2 See the aspect ratio The simplified ratio appears instantly — for example, 1920×1080 becomes 16:9, and 800×600 becomes 4:3. The ratio updates as you type.
- 3 Scale to new dimensions Enter a new width to calculate the correct height, or enter a new height to get the correct width. Both results update at the same time so you can compare options.
Your data stays private
All processing happens entirely in your browser. No files, text, or data are ever sent to our servers. You can disconnect from the internet and this tool will still work.
Frequently asked questions
- What is an aspect ratio?
- An aspect ratio is the proportional relationship between a rectangle's width and height, written as W:H. A 1920×1080 screen has a 16:9 ratio — for every 16 units of width there are 9 units of height. The numbers are simplified to their smallest whole-number form using the greatest common divisor.
- What are the most common aspect ratios?
- 16:9 is the standard for HD and 4K monitors, YouTube, and most modern TVs. 4:3 was the norm for older monitors and SD video. 1:1 is used for Instagram square posts. 9:16 is the vertical format for TikTok, Instagram Reels, and Stories. 21:9 is the ultrawide monitor ratio.
- Why does the ratio matter when resizing?
- If you change width and height independently without keeping the ratio, the image or video gets stretched or squashed. Scaling proportionally means the result looks identical to the original, just at a different size.
- How does the calculator scale dimensions?
- To find the new height: new height = (new width × original height) ÷ original width. To find the new width: new width = (new height × original width) ÷ original height. Both values are rounded to the nearest whole pixel.
- What if my dimensions don't simplify to a clean ratio?
- The calculator always simplifies using the greatest common divisor. Non-standard sizes like 1366×768 give the ratio 683:384, which isn't a named format — but it still lets you scale correctly. For cropping to a named ratio you would need to add or remove pixels.