Aspect Ratio Calculator
The Aspect Ratio Calculator computes the proportional relationship between width and height for displays, videos, and images. Enter any two values — width, height, or target ratio — and get the missing dimension instantly. Supports standard ratios like 16:9, 4:3, 21:9, and 1:1.
🕐 Recent Calculations
What is an Aspect Ratio?
An aspect ratio describes the proportional relationship between the width and height of a rectangle. Expressed as W : H, it tells you the shape of a screen, image, or video frame. A 16:9 aspect ratio means for every 16 units of width, there are 9 units of height — the standard for modern widescreen displays.
Common aspect ratios include 16:9 (HDTV, YouTube), 4:3 (classic TV, presentations), 21:9 (ultrawide monitors, cinema), 1:1 (Instagram square), and 9:16 (TikTok, Stories). Maintaining correct aspect ratios prevents image stretching and distortion during resizing.
使用される計算公式・方程式
この計算ツールは5つの主要な公式を使用しています：
1 Aspect Ratio from Dimensions ▼
Divide both width and height by their GCD. 1920 × 1080: GCD(1920, 1080) = 120. Ratio = 16 : 9.
2 Height from Width and Ratio ▼
Given a width of 1280 and a 16:9 ratio: Height = 1280 × (9/16) = 720 pixels.
3 Width from Height and Ratio ▼
Given a height of 1080 and a 16:9 ratio: Width = 1080 × (16/9) = 1920 pixels.
比率計算ツールの使い方
この比率計算ツールは、以下の3ステップで簡単にご利用いただけます：
数値を入力
入力欄に既知の比率の値を入力します。求めたい未知数の入力欄は空欄のままにしておきます。
モードを選択
比率モード（解く、簡素化、スケーリング）を選択します。各モードで異なる計算式が適用されます。
結果を確認
計算するボタンを押します。結果画面に答えと、視覚的な比率バー、円グラフ、詳細なステップバイステップの解決プロセスが表示されます。
実例問題と段階的な解説
本比率計算ツールを使って、以下の3つの例題をステップバイステップで解決するプロセスです：
入力 1 Find aspect ratio of 2560 × 1440
入力 2 Find height for 1920px wide at 4:3
入力 3 Find width for 1080px tall at 21:9
よくある質問 (FAQ)
What is the most common aspect ratio for monitors? ▼
16:9 is the most common aspect ratio for monitors, TVs, and laptops. Common resolutions include 1920×1080 (Full HD), 2560×1440 (QHD), and 3840×2160 (4K UHD).
How do I calculate the aspect ratio of my screen? ▼
Divide the screen's pixel width by height, then simplify. For a 2560×1080 monitor: divide both by GCD(2560, 1080) = 40, giving 64:27 — an ultrawide ratio close to 21:9.
What aspect ratio is best for YouTube videos? ▼
16:9 is the standard YouTube aspect ratio. Upload at 1920×1080 (1080p) or 3840×2160 (4K). YouTube will letterbox videos with different ratios.
What is the difference between 16:9 and 16:10? ▼
16:9 is wider and flatter, standard for entertainment. 16:10 is slightly taller, common on productivity laptops (e.g., 1920×1200). The extra vertical space helps with documents and coding.
How do I resize an image without changing aspect ratio? ▼
Lock the aspect ratio in your editing software and change only one dimension. The other dimension adjusts automatically. For example, scaling a 1600×900 image to 800px wide automatically sets height to 450px.