how to measure an inch without a ruler

Home » Software » 8 Tools to Measure Length, Width and Height on Your Computer Screen

If you want to know the dimensions of a physical object, you wouldn't necessarily think of turning to your computer first to get some measurements. Of course, there are tools around that can easily tell you how many pixels on the screen it is from one point to another, but actually measuring something in inches or centimeters is a little more tricky.

Whether you want to find out if a button is placed correctly on a webpage or an object is in the correct position in your graphic work, or even if you want the dimensions of a real object but don't have a ruler or tape measure to hand, there are utilities available to help you out.

Here are 8 free options to help you find out a variety of different measurements either in the real world or virtually on the screen.

Before You Start:

To use one of these rulers for more accurate measurements or to measure a physical object, the ruler needs to be calibrated so the inch/centimeter scaling is correct. This differs from screen to screen because of different resolutions and physical screen sizes. Some options offer an ability to calibrate against a real world object of known dimensions, but if they don't, try the following.

You need to know the resolution of the current display (e.g. 1920×1080) and its exact visible display size in inches. (e.g. 21.5). Using a value of 22 inches when your monitor is actually 21.5 inches will produce an inaccurate measurement and needs to be as close as possible.

Once you have this information, visit the PPICalc or DPI / PPI Calculator webpage and enter the horizontal and vertical resolutions, and the diagonal screen size.

Calculate and show PPI

This will output a Pixels Per Inch (PPI) number which you can then enter into the ruler utility if it allows you to for better measurements. Most tools that allow this will let you enter only a whole number without decimal places, so just round up or down. Although it's not 100%, it's still very close.

1. JS Screen Ruler

JS Screen Ruler can display pixels, inches, pica's, or centimeters, and the size of the ruler can simply be extended by dragging the small slider. The right click menu gives you the options to flip the ruler from horizontal to vertical, mark the exact center of the ruler, snap it to the left edge of your desktop screen, and set the pixels per inch for a more accurate measurement as mentioned above.

Jr screen ruler

There is also the shareware Pro version in the zip archive which has a 15 day trial although it only offers functions like color changing and ruler rotation which you probably won't need. JS Screen Ruler is portable and works on Windows 95 up to 7 64-bit.

Download JR Screen Ruler

2. iRuler.net

iRuler is a plain and simple webpage with a static wood effect ruler which you can measure real world objects against, or resize the browser window and drag it to where you want. Make sure to check your monitor dimensions are correct under the ruler.

Iruler net

If they aren't, click the link to select from a small list, or select "even more" to enter your own and input the diagonal size of the monitor and its pixel resolution. For some reason, it asks for aspect ratio even though it really wants the vertical and horizontal screen resolution.

Visit iRuler.net

3. A Ruler for Windows

This measurement utility is more of a web or graphic design tool because it only measures in screen pixels and not centimeters or inches. That makes it no use for measuring real objects but it's useful for any sort of graphics or visual work you do on your PC. As there are no centimeter or inch measurements, A Ruler for Windows doesn't need calibrating.

A ruler for windows

The ruler itself comes with 4 different skins to choose from and a reading guide mode which turns off the numbers and markers so you can use it to read documents or books. The ruler can be flipped into vertical mode and resized or locked into position. There is also a zoom mode that can zoom into your desktop up to 4x to get more accurate measurements, keyboard shortcuts, and various measuring markers.

Download A Ruler for Windows

4. Online Ruler

We found two websites that host this online ruler. The original developer is ginifab.com and another website ursupplier.com hosts a slightly scaled back version. Besides centimeters and millimeters, the ruler can scale down to 1/32 of an inch with optional 1/8 inch markings. The original version is multi language and has a command box so you can tell it to mark certain dimensions (e.g. "show 8 3/4 inches").

Online ruler

Online Ruler is very good for enabling calibration because in addition to using the standard pixels per inch method, it also has options to measure against a real world object. You can use A4 paper, a $1 bill, a €50 note, a £10 note, a CD, or a standard credit/bank card. Hold the item up to the screen and drag the ruler markings to match the object, then press Save to keep the setting for next time. Note the PPI value for future use with this or other rulers.

Visit Online Ruler | Alternate Version

5. Free Online Ruler

This online ruler is pretty simple to use and has measurements for millimeters, centimeters, and inches down to 1/16 of an inch. You can also click and drag the ruler around the browser window as well as holding Ctrl and rotating it through 360°. There are checkboxes to enable/disable centimeter and inch markers and an option to flip the ruler horizontally.

Free online ruler

Click Calibrate and you have options to calibrate the ruler against a real object. You can use a credit/bank card, a US Dollar, a sheet of A4 or Letter size paper, or use another object where its exact size is known. Drag the ruler so the markings match the object you hold up to the screen, then click the calibrate link again when that's done.

Visit Free Online Ruler

6. MB-Ruler

There are quite a lot of advanced options available in MB-Ruler. In addition to measuring distances from one point to another using 6 different scales of measurement, it can also calculate angles with a protractor and includes its own sophisticated coordinates measuring system. A standalone portable version can be created from the options menu.

MB-Ruler

The interface is a semi transparent set square in which the center acts as the starting point for measuring and is simply grabbed and dragged around the screen to change the start point. Other notable features include a color picker, screen capture, a grid system with snapping, screen loupe function, and overlayed shapes and lines or points can be placed around the screen.

Download MB-Ruler

7. Screen Ruler

Besides the fact that it's still actively in development, Screen Ruler has a number of useful functions that should cover most use cases. One of the more interesting is "measure window" that clamps itself to an open window on the desktop giving its width and height. Screen Ruler can display measurements as pixels, points, centimeters, inches, and percent (of screen width), and is available as portable and installer versions.

Screen ruler

The ruler can be shown as vertical, horizontal, or both at once while you can also set its exact size or use a slim scale which makes the ruler thinner. Visual marker aids can be added to the ruler such as center, thirds, custom marker, or golden ratio. if you don't like the color, it can be changed from the settings along with opacity. Calibration could be useful for high resolution monitors because you can adjust the scaling along with entering your own DPI value.

Download Screen Ruler

8. PickPick

PickPick is different to the other options here because it's a free and fully featured screen capture and image editing tool. It includes a number of graphic accessory tools and one of those is a screen ruler. You probably won't want PickPick just for the ruler but if you would like editing or screen capture functions as well, it's a good choice. Just start the program and Pixel Ruler is listed on the right.

Pickpick pixel ruler

You can choose from a vertical or horizontal layout, measure with pixels, inches, or centimeters, choose from four colored skins, and have transparency. The ruler can be finely moved with the arrow keyboard keys. For calibration, you can select from a choice of four DPI (or PPI) settings or enter your own. There is no decimal place PPI value but rounding to the nearest whole number should be close enough.

Download PickPick