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.
我们的免费在线工具
九款免费的浏览器在线工具，覆盖测量、屏幕测试、打印和决策。每一款都完全在浏览器里运行——无需安装、无需账号、无付费墙。
| 工具 | 用途 | 适用场景 | 价格 |
|---|---|---|---|
| 屏幕尺子 | 精确的屏幕在线尺子，支持厘米、毫米、英寸测量物体。 | 设计师、网购者、测量小物件的学生 | 免费 |
| 可打印尺子 | 免费可打印尺子 PDF —— 实际尺寸，无需校准。 | 手工、木工、缝纫、孩子的作业 | 免费 |
| 设备规格 | 收录 69+ 款手机、平板与笔记本的详细屏幕规格。 | 移动开发者、设计师、选购手机的用户 | 免费 |
| 随机转盘 | 随机转盘，适用于决策、课堂和游戏。 | 老师、家庭、团队抽签和抽奖 | 免费 |
| 坏点检测 | 60 秒检测屏幕的坏点、亮点和热点。 | 任何收到新屏幕或维修后的人 | 免费 |
| 量角器 | 在线量角器，可测量 0° 到 360° 任意角度。 | 几何作业、木工、缝纫、照片角度核对 | 免费 |
| 屏幕尺寸计算器 | 根据分辨率和 DPI 计算任意设备的屏幕尺寸。 | 家庭影院规划、显示器选购 | 免费 |
| 像素转换器 | 把 px 转成 rem、em、pt、%、vw、vh —— 即时 CSS 单位转换。 | 前端开发者、CSS 开发、印刷设计调校 | 免费 |
| 长宽比计算器 | 为视频、图片和屏幕计算长宽比。 | 视频剪辑师、社交媒体设计师、图片尺寸 | 免费 |
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.