Aspect Ratio Calculator (16:9, 4:3, 21:9, 1:1)
Enter width × height to calculate the aspect ratio automatically, or pick a ratio (16:9, 4:3, 21:9, 9:16, 1:1) and one dimension to get the matching pixel size. Works for monitors, TVs, photos, video, and social media.
Calculate Ratio
Enter width and height to automatically calculate the aspect ratio.
Calculate Size from Ratio
Enter a ratio and one dimension to calculate the other.
Results are provided for reference only and may differ from actual values.
Common Aspect Ratios & Pixel Dimensions
Quick reference table. Use these presets above to calculate any matching width or height in pixels.
| Ratio | Common Use | Example Pixel Sizes |
|---|---|---|
| 16:9 | HDTV, YouTube, monitors, 4K | 1280×720 · 1920×1080 · 2560×1440 · 3840×2160 |
| 4:3 | Older TVs, iPads, slides, photos | 640×480 · 1024×768 · 1600×1200 · 2048×1536 |
| 21:9 | Ultrawide monitors, cinema | 2560×1080 · 3440×1440 · 5120×2160 |
| 3:2 | DSLR photos, 35mm film | 3000×2000 · 6000×4000 |
| 1:1 | Instagram posts, profile photos | 1080×1080 · 1200×1200 |
| 4:5 | Instagram portrait | 1080×1350 |
| 9:16 | Instagram Stories, TikTok, Reels | 1080×1920 |
| 1.91:1 | Facebook/Instagram landscape | 1200×628 |
How to Calculate Aspect Ratio
Divide the width by the greatest common divisor (GCD) of width and height to simplify. Example: 1920 ÷ 240 = 8, 1080 ÷ 240 = 4.5 → simplified ratio is 16:9.
To resize while keeping the same ratio, use: new_height = new_width × (ratio_height ÷ ratio_width). This tool does the math automatically when you enter any one dimension.
Real-World Usage — Content Creators, Designers, Engineers
YouTube, Streaming, and Video Production
Modern video platforms overwhelmingly use 16:9. Upload at 1920×1080 (Full HD) for standard content, 2560×1440 (QHD) for premium channels, or 3840×2160 (4K UHD) for detail-heavy footage. Thumbnails should match 16:9 (1280×720) — uploading a square image causes YouTube to crop it and may hide the main subject. For cinematic content, consider 21:9 (2560×1080) or 2.39:1 anamorphic, but expect black letterbox bars on 16:9 displays.
Social Media Posts — Platform-Specific Ratios
Getting the wrong aspect ratio is the #1 reason social media images look unprofessional. Quick reference:
- Instagram Feed: 1:1 (1080×1080) or 4:5 (1080×1350 portrait — takes more screen space)
- Instagram Stories / Reels / TikTok: 9:16 (1080×1920)
- Facebook / LinkedIn link preview: 1.91:1 (1200×628)
- X (Twitter) inline image: 16:9 (1200×675) or 2:1 (1200×600)
- Pinterest Pin: 2:3 (1000×1500) — tall pins get more engagement
- YouTube Shorts: 9:16 (1080×1920)
Monitors, TVs, and Ultrawide Setups
Choosing a monitor comes down to aspect ratio as much as resolution. 16:9 is the universal default. 21:9 ultrawide (2560×1080 / 3440×1440) is popular for productivity — you can comfortably place two documents side by side, or immerse in cinema. 32:9 super-ultrawide (5120×1440) replaces a dual-monitor setup. Gaming at 21:9 requires the game to support it; otherwise you get stretched visuals or forced letterboxing.
Photography and Print
DSLR and mirrorless cameras typically shoot at 3:2 (inherited from 35mm film — e.g., 6000×4000 on a 24MP APS-C sensor). Smartphones default to 4:3 (4000×3000 on 12 MP cameras) because sensors are shaped that way. Common print sizes and their ratios:
- 4×6 inches: 3:2 — fits DSLR photos without cropping
- 5×7 inches: 5:7 (≈1:1.4) — needs slight cropping from 3:2
- 8×10 inches: 4:5 — requires noticeable crop from 3:2
- A4 (8.27×11.69 inches): ≈1:1.414 — the √2 ratio
If your photo's aspect ratio doesn't match the print size, the print shop will either crop or letterbox. Pre-cropping in an editor gives you control over what stays in frame.
Common Conversion Mistakes
- 4:3 content on 16:9 displays: Adds pillarbox bars on left/right. Not the same as stretching — stretching distorts faces and logos.
- 9:16 vertical video on 16:9 YouTube: Adds letterbox bars on top/bottom. Use YouTube Shorts or recrop for the main feed.
- "Square" is not 1:1 in all apps: Some platforms accept 4:5 or 1:1; check preview before posting.
Frequently Asked Questions
Q. What is a 16:9 aspect ratio?
16:9 is the standard widescreen ratio for YouTube, TVs, and modern monitors. Typical pixel sizes: 1280×720 (HD), 1920×1080 (Full HD), 2560×1440 (QHD), 3840×2160 (4K UHD).
Q. How do I calculate a 16:9 pixel size?
If you know the width, multiply by 9 ÷ 16 for the height. Example: 1920 × 9 ÷ 16 = 1080. If you know the height, multiply by 16 ÷ 9 for the width.
Q. How do I convert from 4:3 to 16:9?
4:3 and 16:9 have different shapes, so you cannot "convert" without either cropping or adding letterbox bars. To fit 4:3 content inside 16:9, add black bars on the left and right (pillarbox). To fit 16:9 inside 4:3, add bars on the top and bottom (letterbox).
Q. When is a 4:3 aspect ratio used?
4:3 is used in older CRT TVs, iPads, presentation slides, and many classic cameras. Examples: 640×480, 1024×768, 1600×1200, 2048×1536.
Q. What is 21:9 ultrawide?
21:9 is the cinematic ultrawide format used for ultrawide gaming monitors and anamorphic film. Typical sizes: 2560×1080, 3440×1440, 5120×2160.
Q. What aspect ratios does Instagram support?
Instagram supports square (1:1, e.g. 1080×1080), portrait (4:5, 1080×1350), landscape (1.91:1, 1200×628), and 9:16 (Stories/Reels, 1080×1920).
Q. How is aspect ratio width / height calculated?
The aspect ratio is width ÷ height, simplified by the greatest common divisor. For example, 1920 ÷ 1080 = 1.777..., which simplifies to the integer ratio 16:9.
Related Tools
Results are provided for reference only and may differ from actual values. This tool is for informational purposes and should not be used as a basis for legal, financial, or medical decisions.