So, your 100-post blog brings in $2 per day. Will it bring in $4 a day once you write another 100 posts? In many cases, especially for medium-sized blogs that have reached a certain degree of stability, probably not. This is often true even if your traffic does double when you double the number of pages you churn out.

An excellent thread over at Webmaster World discusses why this normally happens:

1. 80/20 principle
   Often, 20% of your pages make you 80% of your earnings. When you double the number of pages you write, are you doubling your money-making pages, or the 80% that make you only 20% of your earnings?
2. Traffic has limits
   I can’t say this better than the forum member that raised the point: “Hey, look at me making $1/day off my Miami Musings. Hey, look at me making $2/day after I double my Miami Musings page count. Hey, how come I’m still only making $2/day even after I wrote 10 times as many Miami Musings pages? Ooops, guess there was a limit on how many people wanted to read about that.”
3. Ad inventory has limits
   Again, don’t let me spoil what he said: “Hey, look at me making $1/day off my Miami Musings. Hey, look at me making $2/day after I double my Miami Musings page count. Hey, how come I’m still only making $2/day even after I wrote 10 times as many Miami Musings pages? Ooops, turns out most of my money was coming from one advertiser, and his AdWords budget was set to $2/day.”
4. You can’t predict
   This point is a subset of the very first point. While all of us take pride in our bid price research, there’s no way you can actually predict how much each keyword is going to bring in. You might end up doubling the number of pages bringing in only $0.20 a click, even though you thought it would bring you 3x that amount.
5. Things change
   How many times have we heard about evil unfair weird Google updates? One day you might rank 3rd for your money-making keyword, the next day, you might end up on page 2. And don’t forget about competition. There’s now so many publishers around, so many blogs around, and more and more full-time bloggers coming up, that someone is bound to smell the cash in your niche.
6. Self-competition
   This threat is even greater in smaller niches where there’s only so much to write about. As you double the number of pages you write, you inevitably create pages with content so similar that they compete with your currently money-making pages. Ever had a product blog where there are 5 or 6 reviews on the same product?
7. High velocity means lousy control
   High post frequency usually implies a sacrifice of control, if not quality. Although you churn out posts on a particular topic by the day, you won’t know how welll they perform until a couple of weeks down the road. Again, this point could be interpreted as one reason why the 80/20 principle holds.

Let me add a couple more:

8. Full scope of traffic not used
   Most bloggers rarely use the full scope of traffic available to them. We often depend on several key sources of traffic, i.e. organic search engine traffic, word-of-mouth traffic, trackbacking, and etc., but ignore paid advertising, directory links, forums, and etc. As a result, you never fulfill the full traffic and thus, earnings potential of your posts. You also reach traffic limits (Point 2) faster than you should.
9. Variation in quality of traffic
   It’s a common phenomenon that traffic from MSN converts better than traffic from Google on certain topics. It’s also common knowledge that repeat visitors don’t click ads as much as new visitors. On a more specific note, we all would love getting Dugg, Boing Boing-ed, and etc., but will that influx in traffic actually raise earnings? Many say: Not by as much as it should.

All this goes to show that a blog double the size, with double the traffic not necessarily brings in double the cash. From the points above, you could summarise that doubling your blog size usually brings in less than double the earnings.

But then, I would have said that in the title if that was the full truth. It happens that it is also true that doubling your blog size could more than double the earnings, because of:

1. Rising authority
   Looking at Point 1 and 6 for example, you may be doubling your lesser performing pages and competing with pages you already have, but you might be tripling your authority in the subject - bringing in more word-of-mouth traffic, getting more backlinks, getting a higher PageRank, and getting a bucket load of traffic from search engines.
2. Complementary pages
   Your 80% of pages that make you crap can, if written well, be complementary pages. They may be the entry pages where visitors first see before navigating to a money-making page. If your $$$ page is on a specific ultra-light notebook model, a complementary but $$$ page might be on the benefits of ultra-light notebooks.
3. Time factor
   The posts that made you zilch half a month ago, might end up making the bulk of your earnings today. Writing about explosive lipstick on a plane a month ago might have been worthless. Two weeks ago on the other hand…

I’m sure you can point out a few more, but the main point is clear. AdSense earnings, or really, earnings from any contextual advertising network (or perhaps even any form of income stream you could leverage through your blog, e.g. affliate marketing), isn’t a linear product of your blog size, the amount of traffic you get, or even the amount of work you put in.

Depressing if you look at this in a negative perspective, isn’t it? I guess that’s why you have probloggers telling you that blogging isn’t easy money. But then, look at it in a positive light, and something like this becomes a possiblity.

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