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アスペクト比計算機

解像度を入力して画面アスペクト比を計算し、比率を保ったままリサイズします。SNS画像サイズのプリセット対応。

Resolution Preset

Width

Height

Aspect Ratio

16:9

Widescreen (TV, Monitor)

Resolution

1920 × 1080

Total Pixels

2.07 MP

2,073,600 px

Megapixels

2.07 MP

Resolution Grade

Full HD

Visual Preview

16:9

Common Resolutions

About Aspect Ratio

• 16:9: Standard ratio for modern TVs, monitors, and YouTube. Used by HD, FHD, and 4K displays.
• 4:3: Classic ratio used by old TVs and iPads. Good for documents and web browsing.
• 21:9: Used by cinema screens and ultrawide monitors. Great for immersive gaming and movies.
• 1:1: Square format, the default ratio for Instagram feed posts.

📖 使い方

Enter width and height in pixels
Or select a resolution preset
View aspect ratio, total pixels, and resolution grade
Use Resize mode to scale while maintaining aspect ratio
Use From Ratio mode to calculate dimensions from one known value

✨ 主な機能

✓Automatic aspect ratio calculation (16:9, 4:3, 21:9, etc.)
✓Various resolution presets (HD to 8K)
✓Social media formats (Instagram, YouTube, etc.)
✓Resize while maintaining aspect ratio
✓Calculate resolution from ratio
✓Total pixels and megapixels display
✓Resolution grade indicator (SD, HD, FHD, QHD, 4K, 8K)
✓Visual aspect ratio preview

📐 計算式

Ratio = Simplify with GCD(width, height) → width÷GCD : height÷GCD

💡 計算原理

•Aspect ratio represents the proportional relationship between width and height, simplified using GCD.
•Example: 1920×1080 has a GCD of 120, resulting in 16:9.
•Same ratio can have different clarity and file sizes depending on resolution.
•Resizing while maintaining ratio prevents image distortion.
•Different social media platforms have different optimal ratios and resolutions.

❓ よくある質問

Q. What is the difference between 16:9 and 21:9?

A. 16:9 is standard widescreen (TV, YouTube), 21:9 is ultrawide (movies, gaming monitors). 21:9 is wider for better immersion but may have letterboxing on some content.

Q. What is the best ratio for Instagram?

A. Feed square: 1:1 (1080×1080), Portrait: 4:5 (1080×1350), Stories/Reels: 9:16 (1080×1920).

Q. What is the recommended YouTube thumbnail size?

A. 1280×720 pixels (16:9 ratio) is recommended. Minimum should be 640×360.

Q. What is the difference between 4K and FHD?

A. 4K (3840×2160) has 4 times the pixels of FHD (1920×1080). Both are 16:9 but 4K is much sharper.

Q. Does resizing while maintaining ratio affect quality?

A. Downscaling usually has minimal quality loss. However, upscaling can cause blur as pixels are interpolated.

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