Auto-detect your screen
Choose auto-detect to apply a starting scale from your browser and device pixel profile. It is the fastest option when you need a quick estimate.
Calibrated screen tools
Measure the real world
from your screen
A fast, accurate online ruler for cm, mm, inches, and pixels. Place it on any edge, calibrate once, and start measuring.
⌁ No download. No account. Works in your browser.Scroll down to see how to use and FAQs.
Free online measuring tool
Online ruler for your screen
OnlineRuler is a practical online ruler that turns your desktop, laptop, tablet, or phone screen into a readable measuring tool. Measure in centimetres, millimetres, inches, or pixels without downloading an app or creating an account.
What can you measure?
Use the online ruler for crafts, school projects, packaging, sewing, jewellery, electronics, DIY, design checks, and everyday objects. The four-edge layout lets you place the scale where it is easiest to align an object, while calibration helps you get a more accurate real-size result.
OnlineRuler is built for convenience: it runs in your browser, works across screen sizes, and lets you change units instantly. It is a virtual ruler, digital ruler, and screen ruler online in one simple interface. Measurements are approximate until you calibrate your display, but the clear markings make quick comparisons easy.
A free online ruler is a convenient way to measure objects, designs, documents, and materials directly on your screen—without needing a physical ruler.
Who Uses a Free Online Ruler?
Graphic & web designers can check dimensions, spacing, margins, and on-screen layouts.
DIYers & makers can take quick measurements whenever a physical ruler isn't available.
Students & teachers can measure worksheets, diagrams, maps, and printed materials.
Photographers & videographers can compare dimensions such as prints, sensors, filters, and other equipment.
Tailors & crafters can measure fabric, paper templates, patterns, and small materials.
Architects & engineers can quickly reference measurements on drawings, plans, and diagrams.
Whether you need a quick measurement or a more precise on-screen measuring tool, our online ruler works directly in your browser on phones, tablets, laptops, and desktop computers. It's completely free, requires no download or account, and is designed for accurate measurements.
Calibrate your screen once, and the ruler can remember your calibration for future visits, making your next measurement even faster.
For longer objects, use the full width of the screen as a 12 inch online ruler or choose a shorter scale such as a 6 inch ruler online. Metric users can switch between a 10 cm, 15 cm, 20 cm, or 30 cm ruler online depending on the available space. These labels describe the visible measuring range; calibration determines how closely the screen matches real-world size.
- Free online ruler with no download or account
- Centimetres, millimetres, inches, and pixels
- Horizontal and vertical ruler placement
- Live hover readings and fullscreen mode
How to use the online ruler
- Choose cm, mm, inch, or px from the floating ruler controls.
- Place your object against the top, bottom, left, or right scale.
- Hover over the scale to see a live measurement in the selected unit.
- For an actual-size ruler result, select Calibrate and follow the screen or card guide.
- Use fullscreen when you need the longest available ruler on your screen.
Improve physical accuracy
How to calibrate your screen
The ruler starts with a screen-size estimate, which is useful for quick checks. For a closer real-world measurement, open Calibrate in the ruler toolbar and choose the method that is easiest for you.
Enter screen diagonal
Choose Screen diagonal and enter the size printed for your display, such as 6.1 or 15.6 inches. The tool uses your screen resolution and diagonal to calculate an estimated PPI.
Pick your device
Select your brand and model when it is listed. The saved display resolution and size provide a useful factory-based scale for supported phones and other devices.
Match a credit card
Choose Credit Card Calibration, place a real standard card over the guide, and adjust the slider until the outline matches the card edges. Save when the fit is exact.
Tip: Calibrate again after changing devices, browser zoom, display scaling, or orientation. A physical calibration is more reliable than an estimate when accuracy matters.
Helpful answers
Online ruler FAQ: how to use a ruler online
Find quick answers about using a free online ruler, measuring in inches or millimetres, and calibrating your screen for an actual-size result.
How to use an online ruler?
To use an online ruler, open OnlineRuler, choose cm, mm, inches, or pixels, and place your object against a screen edge. Read the live marker as you move across the scale, then calibrate the display when you need an actual-size result.
Is there a ruler online?
Yes. OnlineRuler is a free online ruler that works in a browser on desktops, laptops, tablets, Android devices, and phones. This ruler online needs no download, registration, or account.
Can I use my phone as a ruler?
Yes, you can use your phone as a ruler by opening OnlineRuler in a mobile browser. It works as a ruler for phone or iPhone measurements; place the object beside the scale and calibrate for better accuracy.
How to measure cm online?
Select cm in the ruler controls, align the object with the top, bottom, left, or right edge, and follow the centimetre markings. Calibrate the screen first if an online ruler cm measurement must match the physical size.
How to identify 1 inch?
Switch the tool to inches and use the numbered marks: the distance between consecutive whole-number marks is one inch. For an accurate online ruler inches measurement, calibrate your display before measuring a physical object.
How to read a ruler online?
Choose the unit you need, then read the numbered major marks and the smaller divisions between them. This online ruler shows inches, millimetres, centimetres, or pixels, including an online ruler inches vertical scale when the side edge is selected.
Can we measure online?
Yes, you can measure online using a screen ruler for layouts, crafts, schoolwork, and everyday objects. It is an accurate online ruler after calibration, while uncalibrated measurements are estimates based on your display.
Can a smartphone measure?
A smartphone can measure small objects with a ruler for phone screen, but screen size and pixel density affect the result. Use an Android ruler or ruler for iPhone in the browser, then calibrate it for a more accurate measurement.
Can I use my camera as a ruler?
This online ruler uses the visible screen scale rather than the camera, so no camera access is needed. For a reliable result, place the object beside the ruler and calibrate the screen instead of estimating size from a photo.
How to view or add a ruler in Word Online?
In Word Online, open the View tab and turn on Ruler when the option is available in your version. For a quick on-screen measurement outside the document, use this free online ruler and choose cm, mm, or inches.
How to show a ruler in PowerPoint Online?
Open the View tab in PowerPoint Online and enable Ruler if it is available in the web editor. When you need to check a physical size or screen distance, use the calibrated online ruler alongside your presentation.