I know that most graphic design tools have a million rulers built in; but I don’t like the time commitment they take to open and import into. Usually, I first want to know if something is really the size I think it is; or if it needs to be resized.
Most of us do this with guess and check methodology; but JR Screen Ruler is a free and easy on-screen ruler for Windows. So it’s time to return to the old adage: Measure twice, resize once.
Enjoy! - Edward