Frequently Asked Questions (FAQ)

An online ruler calculates the number of screen pixels corresponding to one inch or centimeter based on your display's Pixels Per Inch (PPI). By calibrating your screen using a standard credit card (which is manufactured to an exact width of 85.60 mm / 3.370 inches), the ruler adjusts its scale to match your physical display down to the millimeter.

Every computer monitor and smartphone screen has a different physical size and resolution. For instance, a 1920 × 1080 resolution could exist on a 15-inch laptop or a 65-inch television. Because web browsers only report virtual pixels and cannot automatically know the physical size of your monitor, holding a standard credit card against the screen allows you to lock in your display's exact pixel pitch in seconds.

Yes. The online ruler is fully responsive and supports touch interactions. When using a phone, perform a quick credit card calibration to adjust for your mobile screen's high pixel density. You can then measure small items such as jewelry, coins, screws, and keys directly on your screen.

The bottom edge of our ruler is divided into standard US fractional graduations. The longest marks indicate full inches (1", 2", 3"), the second longest marks indicate half inches (1/2"), followed by quarter inches (1/4" and 3/4"), eighth inches, sixteenth inches, and thirty-second inches. When you click anywhere on the ruler, our tool automatically displays both the simplified fraction (e.g. 2 3/8") and the decimal equivalent (2.375").

In your printer dialog, ensure that the page scaling setting is set to "Actual Size" or "100% Scale". You must disable options like "Fit to Page", "Fit to Printable Area", or "Shrink to Fit", as these shrink the ruler by 4% to 7% and distort measurement accuracy.

We provide separate, dedicated vector PDF downloads for both US Letter (8.5 × 11 inches, standard in the United States and Canada) and ISO A4 (210 × 297 mm, standard internationally).

PPI (Pixels Per Inch) measures the digital resolution of an electronic screen, while DPI (Dots Per Inch) measures the physical print resolution of an inkjet or laser printer depositing ink droplets onto paper.

No. All measurements, calculations, and calibrations run 100% locally in your web browser. Calibrated PPI is saved solely in your local browser storage and is never uploaded or tracked.