While your word processor measures your text in points, in the printing world, text is measured by units called picas. One pica is the equivalent of 12 points. If you were using a ruler, a pica would be the equivalent of 4.217 millimeters. If you use a pica ruler to measure your text, figuring out your point size is straightforward. If you are using a ruler, you can convert your measurement to picas and determine point size.
Using a Pica Ruler
Print the text you would like to measure if it is not already on paper. Even when your word processing program is set to match the exact specifications of printed paper, you are still not seeing the text as accurately as you would on paper.
Lay the pica ruler over your text and measure the picas.
Multiply by 12 for each pica. For instance, if a pica equals 12 points and your text measured out to 2 picas, your text is 24 points.
Using a Standard Ruler
Measure the size of your text in millimeters.
Divide the total number of millimeters by 4.217 -- the equivalent of a pica. For instance, if you measured 21.085 millimeters, divide by 4.217 to get 5.
Multiply the answer you got by 12 to get your point size. For instance, if your answer was 5, multiplying by 12 would give you an answer and point size of 60.
Check your pica ruler to see if there are point size guides. Use the guides to measure your text.