About Screen Ruler Online
What We Do
Screen Ruler Online is a free platform of browser-based measurement and utility tools. Everything runs directly in your browser — no install, no account, no paywall — and works on any modern phone, tablet, or computer.
The platform now hosts nine tools spanning measurement, screen testing, print, and decision-making. The flagship is the Screen Ruler itself — an accurate on-screen ruler in cm, mm, and inches that's reliable to within 0.5 mm once calibrated. The full lineup is documented in Our Free Online Tools below.
The measurement tools share a single calibration system — calibrate once for your screen and the setting is reused across the ruler, protractor, and pixel converter.
How It Works
Every screen has a unique pixel density measured in PPI (Pixels Per Inch). A 13-inch laptop screen and a 27-inch desktop monitor may share the same resolution, but their pixels are physically different sizes. Our calibration process measures this difference so the ruler can accurately convert screen pixels into real-world units.
We maintain a database of popular devices (iPhones, Samsung Galaxy phones, iPads, and more) with their known PPI values. When your device is recognized, we can provide instant measurements. For other devices, the credit card calibration method offers a reliable universal solution. You can read our full step-by-step guide for detailed instructions.
Who Uses Our Tools
The ruler is used in over 100 countries by designers verifying print dimensions, students measuring objects for homework, online shoppers checking product sizes, crafters cutting materials to size, and engineers doing quick physical measurements.
The protractor sees heavy use from woodworkers setting miter angles, sewers and patternmakers drafting darts and pleats, students learning geometry, photographers checking horizon tilt, and hobbyists measuring roof pitch or stair angles on small diagrams.
The spinner is popular with teachers running raffle picks, teams splitting tasks, gamers randomizing drafts, and families settling low-stakes decisions (movie nights, dinner choices).
Supported Devices and Browsers
Screen Ruler Online works in Chrome, Safari, Firefox, Edge, and any modern browser that supports standard web technologies. It runs on iPhones, Android phones, iPads, Android tablets, MacBooks, Windows laptops, Chromebooks, and desktop monitors. No plugins, extensions, or special permissions are needed.
Our device database includes pre-configured PPI values for iPhone 12 through iPhone 15, Samsung Galaxy S23 and S24 series, iPad Pro, iPad Air, iPad mini, Xiaomi Redmi, Realme, OPPO, Vivo, and Samsung Galaxy A-series devices popular in India, Indonesia, and Turkey.
Supported Languages
Screen Ruler Online is available in 20 languages: English, Chinese (Simplified and Traditional), Spanish, French, German, Japanese, Korean, Hindi, Vietnamese, Thai, Turkish, Indonesian, Malay, Filipino, Czech, Romanian, Croatian, Serbian, and Sinhala. We continue to add new languages based on user demand.
Calibration Objects
The ruler supports calibration with multiple reference objects to serve users worldwide: credit cards (ISO standard), US quarters, US pennies, 1 Euro coins, UK pound coins, Indian Rupee coins (5 and 10 denominations), Indonesian Rupiah 1000 coins, Turkish Lira coins, and A4 paper. Open the Screen Ruler and tap the calibration panel to pick from the full list with exact dimensions.
我們的免費線上工具
九款免費的瀏覽器線上工具，覆蓋測量、螢幕測試、打印和決策。每一款都完全在瀏覽器裡運行——無需安裝、無需帳戶、無付費牆。
| 工具 | 用途 | 適用場景 | 價格 |
|---|---|---|---|
| 螢幕間尺 | 精確的屏幕網上尺子，支援厘米、毫米、英寸量度物件。 | 設計師、網購者、測量小物件的學生 | 免費 |
| 可打印間尺 | 免費可列印尺子 PDF —— 實際尺寸，無需校準。 | 手工、木工、縫紉、孩子的功課 | 免費 |
| 裝置規格 | 收錄 69+ 款手機、平板與筆電的詳細屏幕規格。 | 流動開發者、設計師、選購手機的用戶 | 免費 |
| 隨機轉盤 | 隨機轉盤，適用於決定、課室和遊戲。 | 老師、家庭、團隊抽籤和抽獎 | 免費 |
| 壞點檢測 | 60 秒檢測屏幕的壞點、亮點和熱點。 | 任何收到新螢幕或維修後的人 | 免費 |
| 量角器 | 網上量角器，可量度 0° 至 360° 任何角度。 | 幾何功課、木工、縫紉、相片角度核對 | 免費 |
| 螢幕尺寸計算器 | 根據解像度和 DPI 計算任何裝置的屏幕尺寸。 | 家庭影院規劃、螢幕選購 | 免費 |
| 像素轉換器 | 把 px 轉成 rem、em、pt、%、vw、vh —— 即時 CSS 單位轉換。 | 前端開發者、CSS 開發、印刷設計調校 | 免費 |
| 長寬比計算器 | 為影片、圖片和屏幕計算長闊比。 | 影片剪輯師、社交媒體設計師、圖片尺寸 | 免費 |
| PPI 計算器 | 从屏幕尺寸与分辨率计算像素密度——Retina 阈值 + 打印 DPI。 | 选购显示器、判断 Retina 视网膜阈值、按 DPI 反向计算打印所需像素 | 免費 |
Built by Developers, for Everyone
Screen Ruler Online started as a single tool — a calibration-based on-screen ruler — built by a team of web developers who needed a quick way to measure physical objects on screen during design reviews and hardware prototyping. Existing solutions were inaccurate, required downloads, or were cluttered with ads, so we built a clean one and made it free for everyone.
As we worked on the ruler we kept running into adjacent problems that also needed a simple, no-install web tool: measuring an angle on a photo, picking a random item from a short list. That is why the platform now includes a digital protractor and a random spinner alongside the ruler — each one small, focused, and free. The project is actively maintained and regularly updated with new device profiles, calibration objects, tool features, and language support.
Privacy & Data
Your calibration data is stored locally in your browser and is never sent to our servers. We use analytics to understand how people use the tool so we can improve it, but we do not collect any personal information. The ruler does not require an account, does not track individual users, and does not sell data to third parties. Read our full Privacy Policy for details.
Contact
Have a question, found a bug, or want to suggest a feature? We welcome your feedback. Leave us a message and we will get back to you.