# Distribution of E-Book Sales on Amazon

For e-books on Amazon the relationship between the daily sales rate s and the rank r is approximately given by:

s = 100,000 / r

Such an inverse proportional relationship between a ranked quantity and the rank is called a Zipf distribution. So a book on rank r = 10,000 can be expected to sell s = 100,000 / 10,000 = 10 copies per day. As of November 2013, there are about 2.4 million e-books available on Amazon’s US store (talk about a tough competition). In this post we’ll answer two questions. The first one is: how many e-books are sold on Amazon each day? To answer that, we need to add the daily sales rate from r = 1 to r = 2,400,000.

s = 100,000 · ( 1/1 + 1/2 + … + 1/2,400,000 )

We can evaluate that using the approximation formula for harmonic sums:

1/1 + 1/2 + 1/3 + … + 1/r ≈ ln(r) + 0.58

Thus we get:

s ≈ 100,000 · ( ln(2,400,000) + 0.58 ) ≈ 1.5 million

That’s a lot of e-books! And a lot of saved trees for that matter. The second question: What percentage of the e-book sales come from the top 100 books? Have a guess before reading on. Let’s calculate the total daily sales for the top 100 e-books:

s ≈ 100,000 · ( ln(100) + 0.58 ) ≈ 0.5 million

So the top 100 e-books already make up one-third of all sales while the other 2,399,900 e-books have to share the remaining two-thirds. The cake is very unevenly distributed.

This was a slightly altered excerpt from More Great Formulas Explained, available on Amazon for Kindle. For more posts on the ebook market go to my E-Book Market and Sales Analysis Pool.

# Five Biggest Mistakes In E-Book Publishing

Are you thinking about publishing an e-book? If yes, then know that you are entering a highly competetive market. Publishing a book has never been easier and accordingly, many new authors have joined in. To have a chance at being read, you need to make sure to avoid common mistakes.

1. Lack of Writing Experience

Almost everybody can read and write, it’s a skill we learn from an early age on. But writing is not the same as writing well. It takes a lot of practice to write articles or books that make a good read. So before you start that novel, grow a blog and gain experience. This provides a chance to see what works and what doesn’t. And the improvement will become noticeable after just a few weeks and months. As a plus, the blog you grew can serve as a marketing platform once your e-book is finished. In such a competitive market, this can be a big advantage.

2. Writing for Quick Cash

Writing for quick and easy cash is a really bad idea. This might have worked for a short while when the e-books were new and fresh, but this time is long gone. Just browse any indie author forum for proof. The market is saturated. If your first e-book brings in 30 \$ a month or so, you can call yourself lucky. If it’s more, even better, but don’t expect it. Writing and selling e-book is not a get-rich-quick scheme. It’s tough work with a very low ROI. If you do it for the money, you’re in for a disappointment. Do it out of passion.

3. Lack of Editing

If you spend three weeks writing a book, expect to spend another three weeks on fine-tuning and proof-reading. To find the mistakes in the text, you have to go over it again and again until you can’t stand your book anymore. You’ll be amazed that seemingly obvious mistakes (the same words twice, for for example) can be overlooked several times. And no spell checker will find that. Tedious editing is just part of writing and if you try to skip that, you will end up with many deserved one-star reviews.

4. No or Ineffective Marketing

With 2.5 million e-books on Amazon, many of high quality, getting noticed is tough. Without any marketing, your sales will most likely just disappear in an exponential fashion over time. The common marketing means for indie authors are: growing a blog, establishing a facebook fan page, joining facebook groups and interacting, becoming active on twitter, joining goodreads and doing giveaways, free promos via KDP Select, banner and other paid ads (notably on BookBub – as expensive as it is effective), and and and … So you’re far from done with just writing, editing and publishing. You should set aside half an hour a day or so for marketing. And always make sure to market to the right people.

5. Stopping After The First Book

Publishing the first e-book can be a quite sobering experience. You just slaved for weeks or even months over your book and your stats hardly move. Was it all worth it? If you did it out of passion, then yes, certainly. But of course you want to be read and so you feel the frustration coming in. The worst thing you could do is to stop there. Usually sales will pick up after the third or fourth book. So keep publishing and results will come in.

# How E-Book Sales Vary at the End / Beginning of a Month

After getting satisfying data and results on ebook sales over the course of a week, I was also interested in finding out what impact the end or beginning of a month has on sales. For that I looked up the sales of 20 ebooks, all taken from the current top 100 Kindle ebooks list, for November and beginning of December on novelrank. Here’s how they performed at the end of November:

• Strong Increase: 0%
• Slight Increase: 0 %
• Unchanged: 20%
• Slight Decrease: 35 %
• Strong Decrease: 45 %

80 % showed either a slight or strong decrease, none showed any increase. So there’s a very pronounced downwards trend in ebook sales at the end of the month. It usually begins around the 20th. Onto the performance at the beginning of December:

• Strong Increase: 50%
• Slight Increase: 35 %
• Unchanged: 10%
• Slight Decrease: 5 %
• Strong Decrease: 0 %

Here 85 % showed either a slight or strong increase, while only 5 % showed any decrease. This of course doesn’t leave much room for interpretation, there’s a clear upwards trend at the beginning of the month. It usually lasts only a few days (shorter than the decline period) and after that the elevated level is more or less maintained.

# The Ebook Market in Numbers

Over the years the ebook market has grown from a relatively obscure niche to a thrilling billion-dollar mass market. The total ebook revenues went from 64 million \$ in 2008 to about 3 billion \$ in 2012. That’s a increase by a factor of close to 50 in just a few years.

The number of units sold also increased by the same factor (from 10 million units in 2008 to 457 million in 2012).

(Source)

However, many experts believe that the ebook market has reached a plateau and the numbers for the first half of 2013 seem to confirm that.

From the revenues and units sold we can also extract the development of the average price for sold ebooks. It strongly increased from 6.4 \$ in 2008 to about 8 \$ in 2009. After that, it quickly went back down to 7 \$ in 2010 and 6.7 \$ in 2012. So ebooks have gotten cheaper in the last few years, but are still more expensive than in 2008.

As of 2012, ebooks make up 20 % of the general book market.

21 % of American adults have read an ebook / magazine / newspaper on an e-reader in 2012. This is up from 17 % in the previous year.

A survey, again from 2012, shows that most e-book consumers prefer Amazon’s Kindle Fire (17 %, up from no use) , followed by Apple’s iPad (10 %, same as previous year) and Barnes & Noble’s Nook (7 %, up from 2 %).

# Typical Per-Page-Prices for Ebooks

I did a little analysis of ebook prices per 100 pages for different categories in the Amazon Kindle store. In each category I looked at the top 12 paid books. This data can help readers to judge prices and authors to set them. Here are the results in increasing order:

Erotica: 1.7 \$ per 100 pages (ranging from 1.0 – 3.1 \$ per 100 pages)
Sci-Fi and Fantasy: 1.8 \$ per 100 pages (ranging from 0.8 – 4.4 \$ per 100 pages)
Short Stories: 2.0 \$ per 100 pages (ranging from 0.5 – 4.2 \$ per 100 pages)
Self-Help: 3.6 \$ per 100 pages (ranging from 1.3 – 6.7 \$ per 100 pages)
Applied Math: 4.0 \$ per 100 pages (ranging from 0.9 – 7.9 \$ per 100 pages)
Economy / Business: 7.2 \$ per 100 pages (ranging from 3.3 – 17.2 \$ per 100 pages)

Typical (and in my opinion fair) prices seem to be 2 \$ per 100 pages for fiction and 4 \$ per 100 pages for non-fiction. In the special case of business books, prices of 7 \$ per 100 pages seem common.