Rulers are important ones not only for school and colleges but also for home use. Here are some of the list of rulers availble for printing. Also you can go to the website to find more information about these rulers.
One foot ruler
•1 ft long, 3 cm wide. One per page. (centimeters and inches) For US letter-size paper.
•One foot ruler (for A4 paper) 1 ft long, 3 cm wide. One per page.(centimeters and inches) For A4 size paper.
•Metric rulers 25 cm long, 3 cm wide. 6 per page.(centimeters and millimeters)
•Centimeter/Inch rulers : 25 cm long, 3 cm wide. 6 per page.
•Simpler Centimeter/Inch rulers : 25 cm long, 3 cm wide. 6 per page.Fewer ticks, bigger font.
•Decimal-Inch/Centimeter rulers : 25 cm long, 3 cm wide. 6 per page. Ten ticks per inch.
Tips & Warnings
For items longer than the ruler, mark where the ruler ends with a pencil, touch or other method, and begin measuring from the new starting point. Add the lengths together for the total length.

A ruler is a plastic, metal or wooden tool for measuring the distance between two points. Rulers are the common tools in our daily life and you can use the edge of a ruler as a guide in drawing straight lines. Here will introduce you one type of printable paper rulers---narrow rulers.
Narrow Rulers
•Metric rulers (narrow)  25 cm long, 2 cm wide. 9 per page.
•Centimeter/Inch rulers (narrow, parallel) : 25 cm long, 2 cm wide. 9 per page. Both units go in the same direction.
Yardsticks / Meter-sticks
•Meterstick (cm and mm)  : 100 cm long, 2 cm wide. 2 per page.Pieces (4) can be taped or glued together.
•Meterstick (cm and inches) :  A meter is a bit longer than a yard (39+ in).
•Two-meter-stick (cm and inches) : 200 cm long, 2.4 cm wide. One per page.
•Large-print meterstick : 100 cm long, ~5 cm wide. One per page. There are big numbers every 10 cm.
•Large-print meterstick (with 1/4 meter labels) : 100 cm long, ~5 cm wide. One per page.Says “0″, “1/4″, “1/2″, “3/4″, and “1″. But the 10 cm numbers are smaller.
So just go ahead and find out if you have requirement like this. Download the rulers from here

Rulers are the common tools in our daily life and you can use the edge of a ruler as a guide in drawing straight lines. Since there are two main types of rulers in our life, compared with the metric ruler, the interpretation of an English Ruler is different. Here will introduce you the way to read an English Ruler. 
English Ruler
1), Count the number of marks between each number, remembering that the numbers represent inches and the smaller marks are fractions of those inches. Note that English rulers may have eight marks or 16 marks between each inch, but the latter is more common.
2), Look for the three longest marks between two inches. These represent the measurements of fourths: 1/4, 2/4 (or 1/2) and 3/4. Look for the next smallest marks, which represent measurements of eighths: 1/8, 3/8, 5/8 and 7/8. Look for the smallest eight marks, which represent measurements of sixteenths: 1/16, 3/16, 5/16, 7/16, 9/16, 11/16, 13/16 and 15/16.
3), Read an English ruler by looking for the whole number preceding the measurement, and then counting the fractional tick marks, identifying what that measurement is by the sizes specified in Step 2. Leave the answer in fractional form or use a calculator to convert the number to decimal form. For example, a measurement past the 3-inch line and on the third smallest line would be 3 and 5/16 inches, which also equals 3.3125.