正確な画面上での測定、みなさまに。

当社の使命

正確なオンライン定規は簡単な観察から始まりました: 物理的なものを測定する必要があり、定規が近くにない場合、スマートフォンやノートPCが最もよい代替手段です。 Yet most browser-based measurement tools rely on rough estimates, fixed assumptions about screen size, or camera-based approaches that introduce lens distortion and perspective errors.

当社は、これまでにない正確さを備えたオンライン定規を構築することを目指しました — 画面の実際の物理ピクセルグリッドを使用し、複数の校正方法をサポートし、どのズームレベルでもシャープでサブピクセル準確な目盛りを表示します。 The result is a free tool that works on any device, in any browser, without plugins or installations.

精度工学

当社のオンライン定規ツールの中核は、HTML5 Canvas上に直接目盛り、ラベル、分割線を描画するCanvasベースのレンダリングエンジンです。このアプローチにより、すべてのピクセルを完全に制御できます。 — no CSS rounding errors, no sub-pixel blurring, and consistent results across operating systems and browser engines.

Our accurate online ruler supports three independent calibration methods:

• Auto-Detect Device — matches your screen from 130+ known device profiles (iPhone, Samsung Galaxy, Google Pixel, MacBook, Surface, and more) for instant, factory-precise calibration.
• Screen Diagonal — enter your display's diagonal size for a custom PPI calculation based on your screen's native resolution.
• Credit Card Calibration — place any ISO/IEC 7810 ID-1 card on the on-screen guide and adjust until it matches, achieving ±0.5% accuracy.

Once calibrated, the ruler displays at actual scale — a 10 cm line on screen equals exactly 10 cm in the real world. All unit modes maintain this precision, instantly switching without losing calibration.

Why Screen-Based Measurement?

Tools that rely on camera input face fundamental challenges: lens distortion, variable focal length, inconsistent lighting, and parallax error all degrade accuracy. A screen-based approach avoids these problems entirely because your display has fixed physical dimensions and a known pixel grid. By accurately measuring PPI (pixels per inch), the tool renders marks that correspond directly to real-world lengths.

This makes screen-based rulers inherently more reliable than camera-based alternatives. No permission prompts, no camera initialization, no calibration patterns to print — just open the page and start measuring in seconds.

ユーザーセントリックなデザイン

このオンライン定規ツールのすべての機能は、実際の使用パターンを考慮して設計されています: ドラッグ可能な測定ガイド、ロックとアンロック、ダークモード、フルスクリーンモード、フローティングおよびエッジ定規、永続的な設定。

• Dark Mode — comfortable viewing in low-light environments with a full dark theme applied to rulers and controls.
• Fullscreen Mode — distraction-free measuring across your entire display.
• Edge Rulers — rulers positioned precisely at screen edges for maximum workspace.
• Persistent Settings — your PPI, unit preference, and dark mode are saved locally so you never need to recalibrate on the same device.

We also designed for mobile — at 768px and below, the interface adapts with sticky rulers, a compact navigation dropdown, larger touch targets, and optimised layout that preserves full functionality on phones.

当社の約束

正確なオンライン定規は、現在および将来にわたって無料です。アカウント不要、データ収集はしません、測定に干渉する広告もありません。校正データはお使いのデバイスのlocalStorageに保存されます。

We actively maintain and improve the tool based on user feedback. If your device isn't recognised, a measurement seems off, or you have a suggestion, contact us and we will address it promptly.

Device database last verified: July 2026. Calibration methodology reviewed and consistent with ISO/IEC 7810 payment card standards.