20 / Print & Measure
Actual Size Online Ruler
Calibrate your screen with a bank card, move two measurement guides, and read actual millimeters, centimeters, or inches.
Calibrate this display
96 PPI estimatePlace a bank card over the outline. Move the slider until both widths match, then save. Standard card width: 85.60 mm.
Drag either colored guide on the ruler, or use these sliders for fine adjustment.
Calibrate before relying on the physical scale.
Guide-to-guide distance
85.6 mm
Field note
Measure a small object on your screen after one real-world check
A browser knows pixel counts, but it usually does not know the physical size of your display. Matching the blue card outline to a standard bank card gives the ruler a physical reference. The saved value stays on this device.
Actual-size centimeters, millimeters, and inches
The metric scale marks every millimeter and labels centimeters. The inch scale marks sixteenths. Place the object against zero, or move the red and blue guides to its two edges for a live reading in all three units.
Use the ruler on iPhone or Android
Calibrate in the same orientation you plan to use. The ruler is scrollable when 30 cm is wider than the phone. Save / share exports the marked measurement as a PNG to Files, Photos, Drive, Messages, or another supported app.
Printable 12-inch and 30-cm ruler
The PDF uses US Legal landscape so a full 12-inch ruler fits on one page. Print at 100% or Actual Size and verify the included credit-card box before measuring. Use a certified physical instrument when an error could affect safety, fit, health, or money.