Peter Davis' Paper Pixel Ruler

Ever wanted to compute your monitor's DPI?
Or measure something?
…but the closest thing you've got to a ruler is that paper on your desk?

Paper Pixel Ruler to the rescue!

Objects must be smaller than monitor.

Requires Firefox 1.5, Safari 2.0, or Internet Explorer 6.
Flat-screen LCD recommended.


  1. Uncrumple paper
  2. Choose paper size – width, height, or diagonal
  3. Hold paper's edge against screen
  4. Click-and-drag ruler to resize – until paper fits yellow line
Short × Long
US US Letter US Legal US Executive
8.5in × 11in 8.5in × 14in 10.55in × 7.25in
Metric A3 A4 A5 A6
297mm × 420mm 210mm × 297mm 148mm × 210mm 105mm × 148mm
Stuff Index Card CD/DVD 3.5" Floppy
3in × 5in 120mm 3.5in
Photos "4R" "5R" "8R" "12R"
4in × 6in 5in × 7in 8in × 10in 8in × 12in

Click to Resize

Click to Resize
??? pixels ??? DPI
— 8.5in —
Measure the yellow box.

Finished calibrating?

  1. Change mode:
  2. Measure other things on your desk! Hurray!