Free Online Ruler — rulersize.com
A pixel-perfect online ruler that measures in inches, cm, and mm at actual size. Auto-calibrates to your screen — with protractor, set square, and crosshair tools included.
Features
Snap to any edge, switch units instantly, pick the right tool — all in one tab.
⊞
Snap to top, bottom, left, or right edge of your screen. One tap, full-edge span.
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Three unit modes. Switch with a single tap — the ruler redraws instantly.
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Your PPI is saved in the browser. Reopen and it's already perfectly tuned.
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Drag a 30-60-90 triangle overlay over any content. Pinch to scale.
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Drag two arms to measure any angle 0–360° with 0.1° precision.
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Hover (or touch) anywhere and read live X/Y in mm and inches.
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Full dark theme — easier on eyes for low-light measurement work.
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All tools work with touch. Drag, pinch, and tap on any mobile or tablet.
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200+ devices detected instantly — no manual calibration needed.
Calibration
All three persist in your browser so you only calibrate once per device.
We match 200+ devices by user-agent and screen resolution. If your phone, tablet, or monitor is recognised, calibration is instant — no interaction needed.
Enter your screen's diagonal size in inches (on the box or in system info). We derive exact PPI from your native screen resolution.
Place any ISO card (credit, debit, ID) next to the on-screen guide and drag a slider until the widths match. Cards are exactly 85.60 × 53.98 mm worldwide.
Measurement Tools
Three overlay tools that no other online ruler ships. Switch in one tap from the floating toolbar.
⭕
Drag two arms to measure any angle 0–360° with 0.1° resolution. Touch-draggable on mobile.
🔺
30-60-90 draggable triangle overlay. Pinch to scale on touch screens.
✛
Live coordinate readout in mm and inches as you hover or touch anywhere.
How It Works
01
Click "Open Ruler" — no sign-up, no download. Loads in under a second.
02
Auto-detect fills your PPI instantly. Use diagonal or credit card if not recognised. Saved forever.
03
Snap to any edge, pick your tool, and start measuring.
FAQ
Yes — within the tolerance of your calibration. Auto-detect uses factory PPI data; credit card calibration is typically accurate to ±0.1 mm. Keep browser zoom at exactly 100%.
Yes. All tools (ruler, protractor, triangle, crosshair) support touch events. Auto-detect covers most iOS and Android devices.
The ruler shows pixel ticks instead of physical units — useful for UI/design work where you need to count CSS pixels on screen.
No. Calibration data stays in your browser's localStorage. We don't run analytics or tracking scripts.
Browser zoom scales CSS pixels, shifting tick spacing. The ruler detects zoom and shows a correction banner, but 100% is most accurate.
How-To
Yes. Open rulersize.com on any smartphone browser — no app download needed. The site auto-detects most iOS and Android devices and calibrates to the correct PPI instantly. Place any object alongside your screen and read the measurement in inches, cm, or mm. The ruler snaps to any screen edge and responds to touch gestures.
Yes — rulersize.com is a free online ruler that runs entirely in your browser. It measures at actual size in inches, centimetres, and millimetres, auto-calibrates to your specific screen, and requires no download or sign-up.
On our online ruler in inch mode, each full inch is marked by the tallest tick with a number label (1, 2, 3…). Each inch is divided into 16 equal segments — giving 1/16″ precision. Once your screen is calibrated, 1 inch on screen equals exactly 1 physical inch.
Visit rulersize.com and tap the unit toggle to select cm. The ruler draws centimetre and millimetre ticks at true actual size. Place the object you want to measure flat against your screen and read the value where it ends. One-time calibration ensures every centimetre on screen equals exactly 10 mm in reality.
Yes. A smartphone can display an accurate on-screen ruler through a calibrated browser tool like rulersize.com. Open the site — it auto-detects most phones and sets the correct pixel density immediately — then place an object flat against the screen to measure it in inches, cm, or mm. All tools support touch gestures.
Some apps use a phone camera and augmented reality to estimate distances in physical space. Our online ruler works differently: it turns your screen into a precision measurement scale using your display's exact PPI — no camera permissions required. This is ideal for measuring small objects held against the screen.
Absolutely. rulersize.com lets you measure any physical object against your calibrated screen in inches, cm, or mm. After a one-time calibration — which auto-completes instantly for 200+ recognised devices — every measurement is as accurate as a physical ruler. No download or account required.
Reading an online ruler works exactly like a physical one. In inch mode, the tallest ticks mark whole inches, mid-length ticks mark half-inches, and the shortest ticks mark 1/16″ subdivisions. In cm mode, tall ticks are centimetres and short ticks are millimetres. Align the zero end with one side of your object and read the number at the other end.
In Microsoft Word Online, click the View tab in the ribbon and check the Ruler option. This displays Word's formatting ruler above the document — useful for setting margins, indents, and tab stops. Note: this is a layout ruler, not a physical measurement scale. For actual-size measurements, open rulersize.com in a second browser tab.
Go to View in the Word Online ribbon and enable the Ruler checkbox. A horizontal formatting ruler appears above the document area. For real-world physical measurements alongside your document, open rulersize.com in a separate tab — it works perfectly next to Word Online on a wide display.
Open your presentation in PowerPoint Online, click the View tab, then check Ruler. Horizontal and vertical formatting rulers appear along the slide edges to help with alignment. To measure actual printed slide dimensions at true size, open rulersize.com in a parallel browser tab.
Step 1: Visit rulersize.com — your device is auto-detected and calibrated instantly for 200+ recognised devices. Step 2: Select a unit (inches, cm, or mm). Step 3: Snap the ruler to any screen edge. Step 4: Place the object you want to measure alongside the ruler and read the value. No sign-up or download needed.
Open rulersize.com in any browser on phone, tablet, or desktop. If auto-detection recognises your device, the ruler is ready immediately at true actual size. Otherwise, enter your screen diagonal in inches or use the credit card calibration method. Once calibrated, place any object against the screen ruler to measure it in inches, cm, or mm. Calibration is saved for all future visits.
An online ruler is a browser-based measurement tool that turns your screen into a precise scale. Unlike a physical ruler you hunt down in a drawer, a free online ruler is always within reach — on your laptop, desktop, phone, or tablet — with nothing to download and no account required.
Our online ruler tool supports three unit modes you can switch between with a single tap:
Switch between units instantly — the ruler redraws without losing your place.
An online ruler actual size reading depends on knowing your screen's PPI (pixels per inch). Every monitor, phone, and tablet has a different PPI, so a ruler that isn't calibrated to your device will display incorrect measurements. We solve this three ways:
Calibration is saved in your browser's local storage, so every return visit opens a fully configured real online ruler — no repeat setup needed.
A US letter page is 11 inches; A4 paper is 297 mm. The online ruler 12 inch view gives you a continuous scale across most laptop and desktop screens. Snap the ruler to the top or bottom edge, place an object alongside it, and the ruler redraws in real time. On wider monitors the scale can reach well beyond 12 inches — useful for measuring fabric, architectural drawings, and printed photographs. The online ruler inches actual size mode draws ticks at every 1/16" so you can read measurements as precisely as a physical rule.
The actual size online ruler on this site is used every day by people who need a quick, reliable measurement without a physical ruler nearby:
Unlike basic ruler sites, our online ruler tool ships with three overlay tools included at no extra cost. A protractor lets you measure any angle from 0° to 360° with 0.1° resolution. A 30-60-90 set square overlays any content and scales with a pinch gesture. A live crosshair reads X/Y coordinates in mm and inches as you hover or touch anywhere on the screen. All tools support full touch gestures, making this the most complete accurate online ruler available on the web — entirely free, with no sign-up and no tracking of any kind.