Aspect Ratio Calculator
Calculate missing dimensions from an aspect ratio, convert between ratios, and use quick presets for common formats.
Presets
Ratio
Simplified
Known Width → Find Height
Known Height → Find Width
Common Aspect Ratios
| Ratio | Decimal | Common Use |
|---|---|---|
| 16:9 | 1.78 | HD video, YouTube, most monitors |
| 4:3 | 1.33 | Traditional TV, old monitors, some cameras |
| 1:1 | 1.00 | Instagram square posts, icons, avatars |
| 3:2 | 1.50 | DSLR / mirrorless camera standard, 35mm film |
| 2:3 | 0.67 | Portrait photography, Pinterest pins |
| 9:16 | 0.56 | Instagram Stories, TikTok, Reels, mobile video |
| 21:9 | 2.33 | Ultrawide monitors, cinematic video |
| 5:4 | 1.25 | Some monitors, medium format photography |
Understanding Aspect Ratios
An aspect ratio describes the proportional relationship between an image's width and height. An image that is 1920 pixels wide and 1080 pixels tall has an aspect ratio of 16:9 (since 1920/1080 simplifies to 16/9).
Maintaining the correct aspect ratio when resizing is important to avoid stretching or squashing images. In GIMP, the Scale Image dialog has a chain link icon between the width and height fields - Clicking it locks the aspect ratio so both dimensions scale together.
Common Aspect Ratio Mistakes
| Mistake | What happens | Better choice |
|---|---|---|
| Changing width and height separately | Faces, logos, and circles look stretched. | Lock the ratio before resizing. |
| Cropping after resizing | The final image can miss the platform target. | Crop to the target ratio first, then scale. |
| Using one ratio for every platform | Social previews may cut off important details. | Create separate 1:1, 4:5, 16:9, and 9:16 exports. |
For GIMP projects, set the crop tool to a fixed ratio when composition matters. Use this calculator when a client, printer, or social platform gives you one dimension and you need the matching second dimension without guessing.
Exact Pixel Sizes by Platform (2026)
These are the exact pixel dimensions each platform expects. Use the calculator above to adapt any source image to these targets without distortion.
| Platform | Format | Ratio | Pixels |
|---|---|---|---|
| Feed post (square) | 1:1 | 1080 x 1080 | |
| Portrait post | 4:5 | 1080 x 1350 | |
| Instagram / TikTok | Story / Reel / video | 9:16 | 1080 x 1920 |
| YouTube | Video / thumbnail | 16:9 | 1920 x 1080 / 1280 x 720 |
| X (Twitter) | In-stream image | 16:9 | 1600 x 900 |
| Shared link image | 1.91:1 | 1200 x 630 | |
| Shared image | 1.91:1 | 1200 x 627 | |
| Open Graph | Social preview (any site) | 1.91:1 | 1200 x 630 |
| Standard pin | 2:3 | 1000 x 1500 | |
| 4x6 inch photo at 300 DPI | 3:2 | 1800 x 1200 | |
| 8x10 inch photo at 300 DPI | 5:4 | 3000 x 2400 | |
| A4 poster at 300 DPI | 1:1.414 | 2480 x 3508 |
Need to change an image to one of these sizes? Crop to the target ratio first in GIMP using the crop tool with a fixed ratio, then scale to the exact pixels, or use the free image resizer for quick jobs.
Going to print? Check your image has enough pixels with the resolution calculator before sending it off.
Related Tutorial
Master canvas cropping, image scaling, and aspect-ratio-locked resizing with step-by-step instructions.