Practical tools for measured work
How to read a ruler
Select ruler ticks and see reduced inch fractions, decimal inches and millimetres in an interactive reading guide.
Calculate the layout, check the diagram, then print the result for the shop or jobsite.
Choose a tick with the number field or click the diagram. Inch ticks are sixteenths; metric ticks are millimetres. This teaching diagram scales to the page and is not a physically calibrated ruler.
How it works
Count from zero, not from the physical edge of a ruler. Four sixteenth-inch ticks are 4/16 = 1/4 inch = 6.35 mm. Tick 60 is 3 3/4 inches; tick 68 is 4 1/4 inches. One inch is exactly 25.4 mm.
For metric readings, ten millimetres make one centimetre. Check the ruler divisions: not every ruler uses sixteenths, and some start away from the edge.
Related tools
Calibrated screen ruler
Measure screen-plane lengths after physical calibration, with millimetre or sixteenth-inch ticks and zoom/resize invalidation.
Printable Ruler
Prepare a full-size metric, imperial or combination ruler and verify the printed calibration square before use.
Printable Protractor
Prepare a full-size 180° protractor and verify its printed calibration mark before use.
Graph Paper
Create calibrated square or dot-grid paper, draw on it locally, and export a single-sheet PDF or SVG image.