I'm new to wood working and have had and still have a ton to learn. Here are some charts I've found useful. May help someone else I learn everyday.
These are GREAT resources for a newbie
I have taught people to read a ruler in the past and usually that was for people who didn't do so well in math...especially fractions!
you can think about ruler sizes in decimal or in fractions.
(I usually think about them in decimal because I needed to know that for clearance holes for screws or tap diameters)
So for a 1/4-20 screw you would normally pick-up a 5/16 drill for a clearance hole, but since I know a 1/4"screw is .250 and a 5/16 is .3125, for a closer-fit, I knew I needed to move to a letter drill (an F which is 0.257) or larger depending upon the clearance fit desired.
another good trick is dividing fractions...
If you measure 5/8 of an inch and you need to divide it in half - you should know that number is 5/16 (doubling the denominator - the number below the line)
This works all the way up a ruler - if you have a measurement of 5 and 1/4 inches - half of 5 is 2 and 1/2 inches plus half of the 1/4" which is 1/8 so rather than do the math, I halve the big number (2 1/2) and halve the fraction (1/8") and then "count-up" 1/8 from the 2 1/2" to reach 2 and 5/8 of an inch...