Aspect Ratio Calculator
Calculate aspect ratios from any dimensions, lock ratios for proportional resizing, and find the perfect resolution for your screens, images, and videos.
16:9
Decimal: 1.7778
1920 x 1080 px
Resize Calculator
Given a ratio and one dimension, calculate the other.
よくある質問
16:9とはどういう意味ですか？▾
16:9は横幅と高さの比率を表します。幅が16の単位のとき高さが9の単位になることを意味します。現代のHD・4K動画や一般的なPCモニターで標準的に使われるアスペクト比です。
動画サムネイルのサイズを計算するのに使えますか？▾
はい。例えばYouTubeサムネイル（16:9）で幅1280pxの場合、このツールに16:9と1280を入力すれば高さ720pxが即座に計算されます。
カスタムのアスペクト比も入力できますか？▾
はい。Ratioフィールドに任意の比率（例：4:3、21:9、2.35:1）を直接入力できます。コロン区切りで入力してください。
関連ツール
Common Resolutions
| Name | Resolution | Ratio | Pixels | |
|---|---|---|---|---|
| SD (480p) | 640 x 480 | 4:3 | 307,200 | |
| HD (720p) | 1280 x 720 | 16:9 | 921,600 | |
| Full HD (1080p) | 1920 x 1080 | 16:9 | 2,073,600 | |
| QHD (1440p) | 2560 x 1440 | 16:9 | 3,686,400 | |
| 4K UHD | 3840 x 2160 | 16:9 | 8,294,400 | |
| 5K | 5120 x 2880 | 16:9 | 14,745,600 | |
| 8K UHD | 7680 x 4320 | 16:9 | 33,177,600 | |
| Ultrawide FHD | 2560 x 1080 | 21:9 | 2,764,800 | |
| Ultrawide QHD | 3440 x 1440 | 21:9 | 4,953,600 | |
| Instagram Post | 1080 x 1080 | 1:1 | 1,166,400 | |
| Instagram Story | 1080 x 1920 | 9:16 | 2,073,600 | |
| iPad (Standard) | 2048 x 1536 | 4:3 | 3,145,728 |
What Is an Aspect Ratio?
An aspect ratio is the proportional relationship between the width and height of an image, screen, or video. It is typically expressed as two numbers separated by a colon, such as 16:9 or 4:3. The first number represents the width and the second represents the height. Aspect ratios are fundamental in photography, videography, web design, and display technology.
Common Aspect Ratios
Different aspect ratios serve different purposes:
- 16:9 — The standard widescreen ratio used by most monitors, TVs, and YouTube videos. Resolutions include 1920x1080 (1080p) and 3840x2160 (4K).
- 4:3 — The classic ratio used by older TVs and monitors. Common in presentations and iPad displays.
- 21:9 — Ultrawide ratio used by cinematic displays and ultrawide monitors for immersive viewing.
- 1:1 — Square format, popular on Instagram posts and profile pictures.
- 9:16 — Vertical video format used by TikTok, Instagram Reels, and YouTube Shorts.
- 3:2 — Used in many DSLR cameras and the Microsoft Surface line of devices.
How to Use This Calculator
- Enter dimensions — Type a width and height to instantly see the simplified aspect ratio.
- Use presets — Click any common ratio preset to auto-fill dimensions.
- Lock the ratio — Enable ratio lock to proportionally adjust height when you change width, or vice versa.
- Preview — See a visual representation of your ratio in real time.
- Copy results — Copy your calculated ratio or dimensions with one click.
Why Aspect Ratios Matter
Using the correct aspect ratio prevents images and videos from appearing stretched or cropped. When designing for multiple screen sizes, knowing your aspect ratio ensures content displays correctly on phones, tablets, monitors, and TVs. Video editors need to match export ratios to platform requirements, and photographers use aspect ratios to compose shots and prepare prints at standard sizes.