アスペクト比計算機

画像と動画のアスペクト比計算機。幅と高さから比率、小数、スケール表を取得。ワンクリックで結果をコピー。

Aspect Ratio Calculator — Image & Video Ratio Finder Find the exact aspect ratio of any image, video, or screen size with this fast, accurate aspect ratio calculator. Enter a width and height in the aspect ratio calculator and get the simplified ratio, the decimal equivalent, the common name, and a full scale table in one click. What is an aspect ratio calculator? An aspect ratio calculator is a tool that takes a width and height in pixels and reduces them to the simplest whole-number ratio. For example, the aspect ratio calculator converts 1920×1080 to 16:9 automatically. The aspect ratio calculator also identifies the common name (HD / Widescreen), gives the decimal value (1.7778), and generates a table of common sizes at the same ratio. Why use an aspect ratio calculator? Without an aspect ratio calculator you have to compute GCD (greatest common divisor) manually and then divide both dimensions. The aspect ratio calculator does this instantly. The aspect ratio calculator saves time for designers, video editors, photographers, and developers who constantly work with different resolutions and need to match, verify, or scale them. What the aspect ratio calculator calculates When you enter dimensions into the aspect ratio calculator you receive: Simplified ratio: The aspect ratio calculator reduces 3840×2160 to 16:9, 800×600 to 4:3, and any custom size to its lowest terms. Decimal value: The aspect ratio calculator shows the ratio as a decimal (16:9 = 1.7778), useful for setting CSS aspect-ratio or canvas proportions. Common name: The aspect ratio calculator identifies well-known formats such as HD / Widescreen (16:9), Standard TV (4:3), Square (1:1), Ultrawide (21:9), Vertical Mobile (9:16), Photography (3:2), Univisium (2:1), and SXGA Monitor (5:4). Scale table: The aspect ratio calculator generates heights for 320 px, 640 px, 1280 px and 1920 px widths, so you can plan responsive sizes at a glance. Swap button: The aspect ratio calculator lets you flip width and height in one click to check portrait orientation. Copy button: The aspect ratio calculator copies the simplified ratio string to your clipboard. Key features of the calculator - Instant GCD calculation: The calculator finds the exact simplified ratio every time. - Common ratio database: The calculator recognises 8 standard ratios by name. - Decimal equivalent: The calculator shows the floating-point ratio for CSS use. - Scale table for 4 widths: The calculator shows 320, 640, 1280 and 1920 px breakpoints. - Swap W↔H: The calculator handles portrait in one click. - Copy ratio: Copy the output of the calculator with one click. - Error handling: The calculator shows a clear message for invalid inputs. Who uses the calculator? The calculator is used daily by video editors checking export settings, web developers setting responsive image dimensions, UI/UX designers sizing screens and mockups, photographers cropping images, social media managers sizing content for different platforms, and developers using the CSS aspect-ratio property. 100% local and private The calculator runs entirely in your browser. No data is sent anywhere. The calculator requires no login and works offline. Install the calculator once and use it from any Chrome tab. Common ratios supported by the calculator 16:9 (HD Widescreen), 4:3 (Standard TV), 1:1 (Square), 21:9 (Ultrawide), 9:16 (Vertical Mobile), 3:2 (Photography), 2:1 (Univisium), 5:4 (SXGA Monitor). Any other ratio the calculator labels as Custom. Practical examples Video export: You have a 3440×1440 source and need to confirm the format — the calculator instantly shows 21:9 Ultrawide, so you pick the right export preset. Responsive images: A hero image is 2400×1350. The calculator reduces it to 16:9 and the scale table tells you the exact heights for 320, 640, 1280 and 1920 px wide layouts. Social media content: Planning a vertical story? Swap width and height in the calculator and verify the result is 9:16 before you upload. CSS aspect-ratio property: Modern CSS accepts aspect-ratio: 16 / 9 or a decimal. The calculator gives you both forms, ready to paste into your stylesheet.