1. How to Cover Your Book

2. Step 1: Cut Open a Brown Paper Bag
Start by cutting down one corner of the bag, from top to bottom.
Cut around three sides of the bottom flap.
Open the bag up and flatten it out on the table.
You should have a large rectangle with the small rectangle of the bag bottom hanging off one end.

3. Step 2: Cut Off the Bottom Flap
Finish preparing the paper bag by cutting off the bottom flap. This should give you a large rectangular piece of brown paper. 

4. Step 3: Customize the Fit
It is now time to customize the paper to fit the book you need to cover. This requires two simple folds and will ensure that the entire book is protected, no matter its size.
Place the textbook in the center of the paper.
Wrap the paper up and across the bottom of the book and make a crease along the bottom of the cover.
Repeat for the top of the cover. 
Alternatively, you can trace the bottom and top of the book with a pencil.

5. Step 4: Fold Paper at the Top and Bottom
Once you have the outline of where the folds need to be, it's time to make those folds permanent.
Remove the book from the paper and put it aside.
Fold the paper up at the bottom crease (or pencil mark) and down at the top crease (or pencil mark).
You should now have a strip of paper that's just the right size to cover the book from top to bottom.

6. Step 5: Center the Book on the Paper
If you find that you've folded the paper a little too much, no worries -- unfold and start again from Step 3. It's important that the cover is equal to the height of the textbook, no smaller and no more than a tiny bit bigger. Fortunately, the folding and refolding you do won't show.
Place the book back in the center of the paper.
Wrap the paper across the front of the book from left to right and then adjust the book position until the two ends of the paper are even. 
Check for a proper fit.

7. Step 6: Wrap the Cover Around Front of the Book
Your book cover is almost done. To finish the wrapping, take it one side of the cover at a time so you can make final adjustments. We'll begin with the front.
Fold the overlap around the front cover of the book and make a crease.
If the flap is too long, trim it to reach two- thirds to three-quarters of the way across inside of the book cover. 

8. Step 7: Insert the Front Cover
For this step, you will simply insert the book's front cover into your paper folds. The paper cover should fit snugly on the hard textbook cover. It should not be too tight so the paper rips, but also not too loose, which can look a little messy.
Insert the front cover of the book into the slot created by the paper folded over at the top and the bottom of the book cover.
Slide the paper down over the book until you hit the crease.

9. Step 8: Complete the Front Cover
Close the front cover of the textbook, pulling the paper tight across the front of the book. The front cover is now complete.
If you're happy with how it looks, go on to Step 9. If the sizing still isn't quite right, you can go back to Step 3 and try again. Paper bags don't mind being folded and refolded.

10. Step 9: Insert the Back Cover
It's time to do the exact same thing to the back cover that you did on the front. This can be a little trickier because the back may be a little tighter since the front is already done. With a little careful cajoling, it should work out just fine.
Fold the remaining paper around the back cover of the textbook and make a crease. If the flap is too long again, trim it down.
Insert the back cover of the book into the slot created by the paper folded over at the top and the bottom, just as you did with the front cover. 
Slide the paper down over the book until you hit the crease. 
It may help to open the book up and lay it pages-down on a table. Pull the back cover up and toward the front cover and then slip the paper over. Be as careful as you can be so as not to break the spine of the textbook when doing this.

11. Step 10: Write Subject on Cover
If the cover fits snugly, you can stop at this point, sit back, and admire your handiwork.
If it seems a little loose or the top and bottom folds are not lying flat, you can use small pieces of tape to secure the front and the inside flap. Only tape the cover to itself, though. If you tape it to the textbook cover, the pulling and strain of opening and closing may rip the book.
Write the name of the book on the cover and on the spine (for easy finding in your locker).