Smart device detection
Start instantly with a sensible estimate, or choose your exact device from built-in presets.
Free · Private · Works offline
Online Ruler.
Actual size, on your screen.
A precise screen ruler in centimeters, inches, and pixels. Calibrate once, then measure with confidence.
Place an object against the ruler edge
96 px/in · estimated
Tip: browser zoom should be set to 100% for the most accurate result.
Precision, without the fuss
A real ruler, minus the drawer.
Physical size varies between screens. Our calibration tools translate screen pixels into measurements you can trust.
Screen diagonal
Enter the advertised diagonal size of your display for a mathematically precise scale.
Credit card match
Match a standard bank card on screen. No specs, model number, or guesswork required.
Your screen, accurately scaled
A free online ruler for everyday measurements
Measure in inches, centimeters, and millimeters
Actual Online Ruler turns your phone, tablet, laptop, or desktop display into an easy measuring surface. Choose the online ruler in cm for metric work, switch to inches for imperial measurements, or use pixels for digital design. Every centimeter is divided into ten marks, so the same scale works as an online ruler in mm. Place a small object against the selected edge and read its length directly without installing an app. The controls can move the ruler to the top, bottom, left, right, or all four edges, making the tool practical for objects of different shapes and screen positions.
Why screen calibration matters
An online ruler actual size depends on the physical density of your display. Two screens can show the same number of pixels while having very different dimensions. Our calibration options correct that difference. Select a known device, enter your screen diagonal, or resize the credit-card outline until it matches a standard bank card. Once calibrated, the ruler is drawn to scale using the calculated pixels per inch. Your setting is saved only in your browser, so the next visit starts with the same accurate scale and no personal measurement data is uploaded.
How to use the online ruler tool
First, confirm that browser zoom is set to 100 percent. Open Calibrate and choose the method that is easiest for you. Then select cm, in, or px and choose a ruler edge. Align one end of the object with the zero mark and read the mark reached by the other end. For an online ruler inches actual size result, use the inch view after calibration. The eighth-inch divisions make common fractional readings simple. For metric work, use the centimeter view and count the smaller millimeter ticks. You can switch units instantly without losing your saved calibration.
Use a 12-inch ruler when space allows
On a sufficiently wide calibrated monitor, the inch scale functions as a 12 inch online ruler and continues beyond twelve inches when more display space is available. Smaller phones naturally show a shorter section because a true online ruler 12 inch cannot fit on a screen narrower than one foot. Unlike tools that shrink a ruler merely to fit the viewport, this page keeps the online ruler to scale. Scroll-free edge placement and clear numbered marks make it useful for stationery, jewelry, screws, craft materials, printed references, and other compact items.
Private, fast, and available anywhere
This free online ruler runs entirely in the browser. It does not require an account, camera permission, file upload, or measurement history. That makes it a convenient alternative to an online ruler camera app when you simply want to place an object on the screen and compare it with a fixed scale. The page is lightweight, responsive, and usable in light or dark mode. Calibration preferences, unit choice, ruler position, and theme remain on your device through local browser storage and can be changed whenever needed.
Getting the most accurate result
For the most accurate online ruler, use the credit-card method or enter the correct diagonal size for the active display. Recalibrate after moving the browser to another monitor, changing display scaling, or adjusting zoom. Keep the object flat against the screen and view the markings straight on to reduce parallax. This tool is intended for convenient everyday estimates rather than safety-critical engineering or medical work. With those simple checks, Actual Online Ruler provides a practical real online ruler in inches, centimeters, millimeters, and pixels whenever a physical ruler is not nearby.
Questions, measured answers
Online ruler FAQ
Quick answers about measuring on a screen and finding ruler controls in common online tools.
Can I use my phone as a ruler?
Yes. Open Actual Online Ruler on your phone, calibrate it with your device model or a credit card, choose centimeters or inches, and place the object along the selected screen edge. Small objects work best because the usable ruler length is limited by your screen size.
Is there a ruler online?
Yes. Actual Online Ruler is a free browser-based ruler that displays centimeters, millimeters, inches, and pixels. It works without an account or installation and can be placed on any screen edge.
How to identify 1 inch?
One inch equals exactly 2.54 centimeters or 25.4 millimeters. Select the inch mode, calibrate your display, then measure from the zero mark to the tick labeled 1. The smaller ticks divide the inch into eighths.
How to measure cm online?
Set browser zoom to 100%, calibrate the ruler, select cm, and align one end of the object with zero. Read the numbered centimeter reached by the other end. Each small division represents one millimeter.
Can a smart phone measure?
A smartphone can measure small objects with a calibrated on-screen ruler. Some phones also support camera-based augmented-reality measurement, but results vary with camera quality, distance, lighting, and sensor support.
Can I use my camera as a ruler?
Camera and augmented-reality apps can estimate dimensions, but this website does not request camera access. It uses a calibrated actual-size scale on your display, which is more suitable for small objects that can be placed against the screen.
Can we measure online?
Yes. An online ruler can measure objects that fit against your screen. Calibrate the display first, keep browser zoom at 100%, choose a unit, and compare the object with the ruler marks.
How to read a ruler online?
Start at zero rather than at the outer border. Read the last full numbered unit, then count the smaller divisions. In centimeter mode each small tick is 1 mm; in inch mode the small ticks show eighths of an inch.
How to view ruler in Word Online?
In Word for the web, open the View tab and enable Ruler when that option is available. The Word ruler controls document margins and indents; it is different from an actual-size measuring ruler.
How to add a ruler in Word Online?
Open your document in Word for the web, choose View, and select Ruler. If the option is unavailable in your browser or layout, open the document in the desktop Word application and enable View > Ruler there.
How to show ruler in PowerPoint Online?
In PowerPoint for the web, look under the Draw tab for the on-slide Ruler tool. Availability can depend on your account, browser, and input device. This drawing aid helps align ink and objects rather than measure physical size.
How to use online ruler?
Set zoom to 100%, calibrate using a known device, screen diagonal, or credit card, choose cm, in, or px, select an edge, and align your object with zero. Read the tick at the object’s opposite end.
How to add ruler in Word online?
Use View > Ruler in Word for the web. This displays Word’s layout ruler above the document. To measure a real object instead, keep Word in another window and use this calibrated online ruler.
How to use a ruler online?
Calibrate once, choose your preferred measurement unit and ruler position, then place the item flat against the corresponding screen edge. Avoid browser zoom or display-scaling changes after calibration for the most accurate reading.