Chapter 2: Locating information

2.7 Using call numbers to find books

You can think of the call number as the unique address for each item that helps you pinpoint where that item lives on the shelf. Here are the basic rules for reading a Library of Congress call number:

  • Most sections begin with letters and are followed by numbers. Letters in each section are sorted in alphabetical order before the numbers.
  • Numbers in the first section are sorted as whole numbers. (In the example above, the 419 in the first section represents the whole number 419, or four hundred nineteen.)
  • Numbers in later alphanumeric sections are sorted as decimal numbers. (In the example above, the 495 in the second section represents .495 or 0.495, and the same rules apply to the 313 in the third section: you read it as 0.313.)
  • The final section may consist of four numbers with no letters. This is the publication year.

Let’s say you found this book in Quick Search and want to locate it within the library:

One of the items from a search in Quick Search. Arrows point to the item’s call number and the Map it button
Figure 2.13 Call number of a book and Map it button

After you’ve verified that the book is available and in the general collection, you can use the Map it tool to figure out what floor it should be on. You can also use the call number together with the floor maps (located throughout the library) to find the floor where your book should be. The call numbers are arranged in alphabetical order throughout the library’s floors. For our example, books with call numbers starting with SB are on Tier 5.

The same map of floor 2, tiers 4 and 5; but with tier 5 emphasized this time.
Figure 2.14 Map of floor 2, tiers 4 and 5 and approximate location of your book

Once you’re on the right floor or tier, the next step is to find your item on the shelf by using the call numbers displayed at the end of each row of shelves. These numbers represent the first and last books in that row.

Shelves with call numbers. Rows range from SB192-SB21
Figure 2.15 Shelves with call numbers displayed at the end of each row

To figure out if your book is on a particular row of shelves, you first need to know if your book’s call number falls within this range. Usually, reading the first section of your call number will yield this information. You will need to understand this process even if you used the Map it tool, since that won’t show you exactly where your book is located on the shelf.

When reading the call number, start with the letters in the first section. A single letter comes before a two-letter combination starting with that same letter, so S comes before SA when you’re browsing the rows. For example, if a row is labeled with S1204 to SD504, a book with call number SB102 L36 2007 should be in the middle of those shelves, since SB falls between S and SD. In this case, you’ve found the right row and you need to find the book on the shelf.

What if multiple shelves are labeled with call numbers that all start with the same letter or letters? In these cases, you’ll need to compare the numbers in the first section of the call number to determine where among the rows your item should be. Your book’s call number is SB102 L36 2007 and its first section is SB102. In the example above, our rows have the following range: SB21 to SB123. You don’t need to worry about any of the other numbers or letters in the call number yet, just focus on the beginning to find the right row of shelves.

As we mentioned in the previous section, the number in the first segment of a call number is sorted as a whole number. This means that 15 (fifteen) comes before 100 (one hundred). In our example, the book with a call number starting with SB102 (SB one hundred two) should be on the row of shelves with the range SB21 (SB twenty-one) to SB123 (one hundred twenty-three).

Finding your book on the shelf

Now that you’ve found the specific row of shelves your book is on, you can locate your book on the shelf! You’ll need to skim through the call numbers of the books already on the shelf to figure out whether your book’s call number comes before or after them. This is similar to skimming door numbers when trying to locate a friend’s room in the dorms. You want to make sure you’re on the right floor and around the correct numbers to find them.

Tips for skimming books

When comparing call numbers, don’t worry about reading through the entire call number every time. Instead, start at the top, work your way right and down, and look for the first place where the call numbers of the books on the shelf differ from the one you want. Did you pass where your book should be, or is it farther down the shelf?

For example, let’s say you are looking for TL799 P59 S74 2018, and run across items with the following call numbers:

  • TK9 K37 1996
  • TK531 K56x 1978
  • TK5102 R79 2006
  • TK5103 B58 2011

TL799 P59 S74 2018 starts with TL, so you don’t need to read the rest of the call number to know that this book is farther down the shelf.

Once you’ve found items that match the first part of your call number, use the second part to locate your item. Similar to the first part, this section starts with a letter or set of letters. These are arranged alphabetically. In most cases, you’ll need to find the other items matching the first letter(s) in the second part before moving to the number that follows.

Unlike in the first part of the call number, the number in the second part should be treated as though it has a decimal point in front of it, although it may not display one. Our item, SB102 L36 2007, would come between SB102 L3 and SB102 L4 because 0.36 is between 0.30 and 0.40. One way to think about the differences between numbers in the first and the second segment of the call number is that the first is a whole number, like a dollar, and the second is a decimal, like cents or change.

The final part of a call number is often a four-digit number with no letter. This represents the year of publication. Not all call numbers include a publication year, but if it is present and all other parts of the call numbers are identical, you can sort the items by putting the publication dates in chronological order. When the library owns more than one edition of a book, the call numbers for each edition will often be identical up to the publication year. Our call number, SB102 L36 2007, does have the year displayed as the last segment, but we don’t have any other editions for you to sort through.

Once you find your book, it often pays to examine the other items shelved nearby. Those items are often about similar topics to the item you were originally seeking, and may be a valuable addition to your research project.

Common problems and how to solve them

  1. There are multiple rows of shelves that have the same first part as your call number: Do not despair! Compare the next part of the call number to the labels on the rows of shelves to check where your call number fits.
  2. Your call number is formatted differently from the examples we’ve shown: Some items don’t have typical Library of Congress call numbers. An example is TA1 Am35p. Even though it seems strange, you can still use alphanumeric order to narrow down where it should be on the shelf.
  3. Your book is not where you think it should be:
    • Check the surrounding area on the shelf or behind the books on the bottom shelf (it may have fallen).
    • Check the reshelving area on that floor, where books used within the library are placed before being put back on the shelves.
    • Verify in Quick Search that it’s in the General Collection and that it is not checked out.
  4. You still can’t find your item: Ask for help at the Main Desk.

Check your understanding

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Library 160: Introduction to College-Level Research by Iowa State University Library Instruction Services is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted.