Four ways to calibrate.
Use automatic detection, select a known device, enter your display diagonal, or match a standard bank card.
Place a ruler on any edge.
Choose an edge from the toolbar, or select a shortcut below.
⌾ Your calibration stays on this device. Nothing is uploaded.
Built for real measurements
Accurate by design.
Browser pixels are not physical units. OG Ruler accounts for your display so the scale on screen matches the object in your hand.
Every edge is useful.
Place rulers on the top, right, bottom, or left independently—ideal for objects, layouts, and two-axis checks.
More than a ruler.
Pin guides, track live X/Y coordinates, measure a two-point area, save results, and enter fullscreen.
Measure directly on your screen
Online Ruler for Actual-Size Measurements
OG Online Ruler is a free online ruler that turns the edge of your screen into a practical measuring tool. Choose centimeters, millimeters, inches, or pixels, calibrate your display, and compare an object against a scale shown at actual size.
Measure in cm, mm, inches, and pixels
Use the unit selector to switch between an online ruler in cm, an online ruler in mm, an inch scale, and pixels. The centimeter scale includes smaller millimeter marks, so the same view works as an online ruler cm tool and a precise mm online ruler. If you prefer imperial measurements, select inches to measure everyday objects or check dimensions against an online ruler inches display.
The scale can appear on the top, bottom, left, or right edge. Turn on more than one edge when you need horizontal and vertical references together. Numbering follows the measuring direction, while clear major and minor marks help you read values quickly. You can also pin a guide anywhere on the canvas, drag it to a new position, use arrow keys for fine adjustment, or remove it when the measurement is complete.
Calibrate the ruler to actual size
An accurate online ruler must account for differences between screens. Browser pixels do not always match physical pixels, and two displays with the same resolution can have different dimensions. OG Online Ruler offers several calibration choices: automatic device detection, a known device profile, screen diagonal entry, and credit card calibration. Matching the on-screen card outline to a standard bank card is usually the most dependable option.
After calibration, the online ruler actual size scale is calculated using your screen’s pixel density. This makes the tool more reliable than assuming every display uses the browser default. For the best result, set browser zoom to 100 percent, keep the browser maximized, and recalibrate after moving the window to another monitor. Your calibration is stored only in your browser and is not uploaded.
Use an actual-size ruler for everyday tasks
A real online ruler is useful when a physical ruler is unavailable. Measure a button, screw, coin, cable, craft component, jewelry item, printed detail, or small package. Designers and developers can switch to pixels to inspect spacing and screen elements. Students can compare metric and imperial units, while makers can place an object against two active edges to estimate width and height.
Need a 12 inch online ruler? Select inches and use fullscreen mode to display as much scale as your monitor allows. Whether a complete online ruler 12 inch span fits depends on the physical width of your screen. A phone cannot show twelve physical inches at once, while many desktop monitors can. Calibration ensures every visible inch remains correctly sized even when the entire twelve-inch length is not available.
Fast, private, and easy to control
The ruler runs directly in the browser with no account, download, or upload. Unlike an online ruler camera experience, it does not need camera permission or analyze images. Place the item gently against the screen without pressing, choose the nearest ruler edge, and read the endpoint. The crosshair displays live horizontal and vertical coordinates, while Measure Box lets you drag between two points and see both dimensions together.
Keyboard shortcuts make repeated measurements faster: press 1 for centimeters, 2 for inches, 3 for pixels, G for guides, C for the crosshair, F for fullscreen, and D for dark or light mode. These controls make OG Online Ruler a flexible online ruler tool for quick checks as well as careful comparisons. Start with calibration whenever physical accuracy matters, then choose a unit and measure directly against the scale.
Work faster
Keyboard fluent.
1 Centimeters2 Inches3 PixelsG GuidesC CrosshairF FullscreenD ThemeH Quick guide
Online ruler questions
Frequently asked questions.
Can I use my phone as a ruler?+
Yes. Open OG Online Ruler on your phone, calibrate the display, select centimeters or inches, and place a small object along an active ruler edge. A phone screen can only measure objects that fit within its physical width or height.
Is there a ruler online?+
Yes. An online ruler displays a measurement scale directly in your browser. OG Online Ruler works without an installation and supports centimeters, millimeters, inches, pixels, movable guides, and rulers on any screen edge.
How can I identify 1 inch?+
One inch equals exactly 2.54 centimeters or 25.4 millimeters. Select inches, calibrate your screen, and measure from the zero mark to the first numbered inch mark. Keep browser zoom at 100 percent for the most reliable result.
How do I measure centimeters online?+
Select cm in the Units control, calibrate the ruler using your device, screen diagonal, or a bank card, then align the object with the zero edge. Read the numbered centimeter mark at the object’s endpoint; the smaller divisions represent millimeters.
Can a smartphone measure objects?+
A smartphone can estimate dimensions with an on-screen ruler or a dedicated sensor-based measuring app. An on-screen ruler is best for small, flat objects. Accuracy depends on correct screen calibration and careful alignment.
Can I use my camera as a ruler?+
Some augmented-reality apps estimate dimensions through a phone camera, but OG Online Ruler does not request camera access. It measures small objects against a calibrated scale displayed directly on your screen.
Can we measure objects online?+
Yes. A calibrated browser ruler can measure objects that fit against the screen, while image-based tools can estimate dimensions when a known reference object is included. For physical on-screen measurements, calibrate first and keep browser zoom at 100 percent.
How do I read a ruler online?+
Start at zero, align the object with the ruler edge, and note where its other end stops. Large numbered marks show the selected main unit. In centimeter mode, ten smaller divisions equal one centimeter; each small division is one millimeter.
How do I view the ruler in Word Online?+
In Word for the web, open the View tab and look for the Ruler option. Availability can vary by document mode and Microsoft’s current interface. If it is unavailable, open the document in the desktop Word app to use the full ruler controls.
How do I add a ruler in Word Online?+
Open the document, choose View, and enable Ruler when that option is available. The Word ruler controls paragraph indents, tab stops, and margins; it is a document-layout aid rather than a physical measuring ruler.
How do I show the ruler in PowerPoint Online?+
Open the presentation and check the View tab for Ruler. Microsoft may expose different controls in the web and desktop editions. If the option is missing in PowerPoint for the web, open the file in the desktop application.
How do I use an online ruler?+
Set browser zoom to 100 percent, calibrate the screen, select cm, inches, or pixels, and choose the ruler edge nearest your object. Align one end at zero and read the endpoint. Use movable guides, the crosshair, or Measure Box for easier comparison.