Web tool · updated
Aspect ratio calculator
Type a width and height to get the aspect ratio, then a new width or height to resize without stretching. You also get the exact sizes GPT Image, Nano Banana and Midjourney accept for that shape, and you can crop an image to any ratio without uploading it.
- Any size → ratio
- Resize without stretching
- Nano Banana + GPT Image sizes
- Crop in your browser
Aspect ratio calculator
Common ratios
Type a new width or height; the other keeps your ratio, rounded to whole pixels.
Aspect ratio
16:9
1.78:1
Exactly 16:9, landscape. HD and 4K video, YouTube, TVs, presentations.
Standard sizes at this ratio: 720p HD 1280×720, 1080p Full HD 1920×1080, 1440p QHD 2560×1440, 4K UHD 3840×2160
Sizes for AI image generators at 16:9
| Model | Use | Sizes |
|---|---|---|
| GPT Image | size = any multiple of 16 | |
| Nano Banana 2.1 | aspect_ratio = | 1K 1376×768 · 2K 2752×1536 · 4K 5504×3072 |
| Nano Banana Pro | aspect_ratio = | 1K 1376×768 · 2K 2752×1536 · 4K 5504×3072 |
| Nano Banana (2.5 Flash Image) | aspect_ratio = | 1344×768 |
| Midjourney | Add to the end of your prompt |
Crop an image to a ratio
Your crop preview shows here.
▸ Steps
How to use the aspect ratio calculator
- 1
Enter a size
Type the width and height in pixels, pick a common ratio, or choose an image to read its size.
- 2
Resize it
Type a new width or height. The other side updates so the picture keeps its shape.
- 3
Copy AI sizes or crop
Copy the matching GPT Image size, Nano Banana ratio or Midjourney --ar, or crop your image to a ratio and download it.
▸ The maths
How to calculate aspect ratio
An aspect ratio is width compared with height. To find it, divide both by their greatest common divisor (the biggest number that goes into both). 1920 and 1080 share 120, so 1920×1080 is 16:9. 1080×1350 shares 270, so it's 4:5.
To resize without stretching, scale both sides by the same amount: new height = new width × original height ÷ original width. A 1920×1080 frame at 1280 wide is 1280 × 1080 ÷ 1920 = 720 tall.
Some "ratios" are rounded names. Ultrawide monitors sold as 21:9 are really 64:27 at 2560×1080 (2.37:1) and 43:18 at 3440×1440 (2.39:1). True 21:9 is 2.33:1. The calculator shows the exact ratio and the nearest common name.
▸ Reference
Common aspect ratios and sizes
| Ratio | Decimal | Example size | Used for |
|---|---|---|---|
| 1:1 | 1:1 | 1920×1920 | Square posts, profile pictures, album art |
| 5:4 | 1.25:1 | 1920×1536 | Large-format prints, some monitors |
| 4:3 | 1.33:1 | 1920×1440 | Older TVs and monitors, iPad, most phone photos |
| 3:2 | 1.50:1 | 1920×1280 | 35mm film and most camera sensors, 4×6 prints |
| 16:10 | 1.60:1 | 1920×1200 | Laptop and desktop displays |
| 16:9 | 1.78:1 | 1920×1080 | HD and 4K video, YouTube, TVs, presentations |
| 21:9 | 2.33:1 | 1920×823 | Ultrawide monitors and cinema-style video (marketing name) |
| 32:9 | 3.56:1 | 1920×540 | Super-ultrawide monitors |
| 4:5 | 1:1.25 | 1536×1920 | Portrait social posts |
| 3:4 | 1:1.33 | 1440×1920 | Portrait photos |
| 2:3 | 1:1.50 | 1280×1920 | Portrait prints and posters |
| 9:16 | 1:1.78 | 1080×1920 | Vertical video: Reels, Shorts, TikTok, Stories |
▸ AI images
Sizes for AI image generators
AI image models don't take any size you like. Nano Banana (Google's Gemini image models) takes a fixed list of ratios, each with set pixel sizes. GPT Image takes any size that follows OpenAI's rules. Midjourney takes a whole-number ratio after --ar. Ask for a shape a model doesn't support and it picks the nearest one, so crop to your final ratio afterwards.
| Nano Banana 2.1 ratio | 1K | 2K | 4K |
|---|---|---|---|
| 1:1 | 1024×1024 | 2048×2048 | 4096×4096 |
| 1:4 | 512×2048 | 1024×4096 | 2048×8192 |
| 1:8 | 384×3072 | 768×6144 | 1536×12288 |
| 2:3 | 848×1264 | 1696×2528 | 3392×5056 |
| 3:2 | 1264×848 | 2528×1696 | 5056×3392 |
| 3:4 | 896×1200 | 1792×2400 | 3584×4800 |
| 4:1 | 2048×512 | 4096×1024 | 8192×2048 |
| 4:3 | 1200×896 | 2400×1792 | 4800×3584 |
| 4:5 | 928×1152 | 1856×2304 | 3712×4608 |
| 5:4 | 1152×928 | 2304×1856 | 4608×3712 |
| 8:1 | 3072×384 | 6144×768 | 12288×1536 |
| 9:16 | 768×1376 | 1536×2752 | 3072×5504 |
| 16:9 | 1376×768 | 2752×1536 | 5504×3072 |
| 21:9 | 1584×672 | 3168×1344 | 6336×2688 |
- Nano Banana Pro uses the same sizes for its 10 ratios (no 1:4, 4:1, 1:8 or 8:1).
- GPT Image: sides in multiples of 16, long side up to 3,840 px, between 1:3 and 3:1, 655,360–8,294,400 pixels in total. OpenAI marks sizes above 2560×1440 as experimental.
- Midjourney: add
--ar 16:9(or any whole-number ratio) to the end of the prompt.
Checked on against the Gemini image generation docs and OpenAI image generation guide.
▸ FAQ
Questions
What aspect ratio is 1920×1080?
16:9. Divide both numbers by their greatest common divisor, 120, and you get 16 and 9. 1280×720, 2560×1440 and 3840×2160 (4K) are 16:9 too.
What is 16:9 in pixels?
Any size where the width divided by the height is 1.78. Common ones: 1280×720 (720p), 1920×1080 (1080p), 2560×1440 (1440p) and 3840×2160 (4K UHD).
What size is a 9:16 vertical video?
1080×1920 is the usual size for Reels, Shorts, TikTok and Stories. It's 16:9 turned on its side, so 720×1280 works too at lower quality.
How do I resize an image without stretching it?
Keep the ratio: new height = new width × original height ÷ original width. If you need a different ratio, crop the image or pad it with a border; changing only one side stretches it.
Which aspect ratios does Nano Banana support?
Nano Banana 2.1 takes 14 ratios: 1:1, 1:4, 1:8, 2:3, 3:2, 3:4, 4:1, 4:3, 4:5, 5:4, 8:1, 9:16, 16:9, 21:9. Nano Banana Pro and the original Nano Banana take 10: 1:1, 2:3, 3:2, 3:4, 4:3, 4:5, 5:4, 9:16, 16:9, 21:9. Ask for anything else and you get the nearest one.
What sizes can GPT Image make?
Any width × height where both sides are multiples of 16, the long side is at most 3,840 px, the shape is between 1:3 and 3:1, and the total is 655,360 to 8,294,400 pixels. OpenAI recommends 1024x1024, 1536x1024, 1024x1536.
Is my image uploaded anywhere?
No. The image is read and cropped by your browser, and the PNG is made on your device. Nothing is sent to QuestLoops or anyone else.
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