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.
무료 온라인 도구
측정, 화면 테스트, 인쇄, 결정을 위한 9가지 무료 브라우저 기반 도구. 각 도구는 브라우저 안에서 완결됩니다 — 설치, 계정, 페이월 모두 없습니다.
| 도구 | 용도 | 추천 대상 | 가격 |
|---|---|---|---|
| 화면 자 | cm/mm/인치 단위로 물체를 측정하는 정확한 화면 자. | 디자이너, 쇼퍼, 작은 물건을 재는 학생 | 무료 |
| 인쇄용 자 | 무료 인쇄용 자 PDF — 실제 크기, 교정 불필요. | 공예, 목공, 바느질, 아이 숙제 | 무료 |
| 기기 사양 | 69종 이상의 스마트폰, 태블릿, 노트북 화면 사양 데이터베이스. | 모바일 개발자, 디자이너, 스마트폰 구매자 | 무료 |
| 무작위 돌림판 | 의사 결정, 교실, 게임용 랜덤 스피너. | 교사, 가족, 팀 추첨 및 경품 | 무료 |
| 죽은 픽셀 테스트 | 60초 만에 죽은 픽셀, 고정 픽셀, 핫 픽셀을 테스트. | 새 화면이나 수리품을 받은 모든 사람 | 무료 |
| 각도기 | 0°부터 360°까지 각도를 측정하는 온라인 각도기. | 기하 숙제, 목공, 바느질, 사진 각도 확인 | 무료 |
| 화면 크기 계산기 | 해상도와 DPI로 모든 기기의 화면 크기를 계산. | 홈시어터 빌더, 모니터 구매자 | 무료 |
| 픽셀 변환기 | px를 rem, em, pt, %, vw, vh로 즉시 변환하는 CSS 단위 변환기. | 프런트엔드 개발자, CSS 작업, 인쇄 디자인 보정 | 무료 |
| 화면 비율 계산기 | 동영상, 이미지, 화면의 화면 비율을 계산. | 비디오 편집자, 소셜 미디어 디자이너, 이미지 크기 | 무료 |
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.