Aspect Ratio Calculator
Calculate aspect ratios and resize width and height while keeping the same proportions. Enter an original width and height to see the simplified ratio (like 1920×1080 → 16:9), then type a new width or height and instantly get the matching dimension that preserves the ratio. Ideal for resizing images, videos, and screens, planning responsive layouts, and converting between common ratios like 16:9, 4:3, and 21:9.
Type a new width or height and the other is calculated to match the ratio above.
ToolsSoup's Aspect Ratio Calculator works out the proportional ratio between a width and a height and resizes either dimension while keeping that ratio intact. Enter an original width and height to see the simplified ratio — for example, 1920 × 1080 reduces to 16:9 — then type a target width or height and instantly read the matching dimension. It's the quickest way to resize images and videos without distortion, plan screen and layout sizes, and convert between popular ratios like 16:9, 4:3, 3:2, and 21:9. Everything runs in your browser: no uploads, no sign-up, and your numbers never leave your device.
What is an aspect ratio calculator?
An aspect ratio calculator finds the proportional relationship between a width and a height and uses it to scale dimensions up or down without stretching. The aspect ratio is written as width:height — 16:9 for most TVs and monitors, 4:3 for older displays, 1:1 for square images. The calculator reduces any width and height to their simplest whole-number ratio using the greatest common divisor, so 1920 × 1080 becomes 16:9 and 800 × 600 becomes 4:3. Once the ratio is set, entering one new dimension gives you the other automatically, guaranteeing the result has exactly the same shape as the original.
How to use the aspect ratio calculator
Calculating or applying an aspect ratio takes just a few steps, and the results update as you type:
- Enter the original width and height (or click a preset like 16:9) to set the aspect ratio.
- Read the simplified ratio shown in the result panel.
- Type the new width you want — the matching height is filled in automatically.
- Or type the new height instead, and the width is calculated to keep the same ratio.
- Copy the result if you need it for your image, video, or layout.
Common aspect ratios and where they're used
16:9 is the standard for HD and 4K video, YouTube, and almost all modern monitors and TVs. 4:3 was the classic ratio for older televisions, presentations, and many cameras. 3:2 is common in DSLR and mirrorless photography and many laptop screens. 21:9 (and 32:9) are ultrawide ratios used for cinematic video and gaming monitors. 1:1 is the square format favored by profile pictures and many social posts, while 9:16 is the vertical ratio for phone screens, Stories, Reels, and TikTok. Set any of these with the preset buttons, then resize to the exact pixel dimensions you need.
Resizing images and videos without distortion
To resize an image or video cleanly, the new dimensions must share the same aspect ratio as the original — otherwise the picture is stretched or squashed. Enter your source width and height to lock in the ratio, then change just one dimension. If you scale a 1920 × 1080 image to a width of 1280, this calculator returns a height of 720, keeping it perfectly 16:9. The same approach works for thumbnails, social media crops, responsive layout boxes, and print sizes — change one number and let the calculator protect the proportions.
Why use this aspect ratio calculator?
- Reduces any width and height to a clean, simplified ratio like 16:9 or 4:3.
- Resizes width or height automatically while preserving the exact ratio.
- Includes one-click presets for 16:9, 4:3, 21:9, 3:2, 1:1, and 9:16.
- Handles whole numbers and decimals, and updates live as you type.
- Runs entirely in your browser — free, no ads, and your numbers never leave your device.
Frequently asked questions
How do I calculate an aspect ratio?
Divide the width by the height to get the ratio, then reduce both numbers by their greatest common divisor to express it in simplest whole-number form. For example, 1920 ÷ 1080 simplifies to 16:9. This calculator does that automatically — just enter the width and height.
What aspect ratio is 1920 × 1080?
1920 × 1080 is 16:9, the standard widescreen ratio used for HD and 4K video, monitors, and TVs. Both numbers divide by 120, giving 16 and 9. Enter 1920 and 1080 above to confirm it.
How do I resize an image while keeping the aspect ratio?
Enter the original width and height to set the ratio, then type the new width or height you want. The calculator fills in the other dimension so the resized image stays perfectly in proportion with no stretching or cropping.
What is the difference between 16:9 and 4:3?
16:9 is a wide format (the width is about 1.78 times the height) used by modern screens and video. 4:3 is closer to square (the width is about 1.33 times the height) and was standard on older TVs, monitors, and presentations. Switching from 4:3 to 16:9 means a wider, shorter frame for the same width.
Does this calculator work with decimal sizes?
Yes. If your width and height aren't whole numbers, the calculator shows the ratio as a decimal value to 1, and still resizes either dimension to keep that exact proportion. It works for both pixel-perfect integers and fractional measurements.