There seems to be an endless race to produce consumer cameras with more and more megapixels. In the complicated world of digital photography, it is easier to explain that a camera with 7mp must be worth more than a camera with 5 mp. But, the question is does a camera with more MP produce better pictures? Isn’t 7 better than 5? Certainly 5 is better than 3. True? Well, not always. 

There are many factors that go in to making a digital camera. The amount of pixels is just one of the factors and it is a significant contributor to overall quality of the camera but it is not the only one. There are amateur cameras available with more pixels than some professional cameras selling at 5 times their price yet when the results from the two cameras are compared it becomes obvious that the professional image, taken with fewer pixels, is far superior. The reason for the disparity in quality is not caused by the amount of pixels, but the quality of the pixels. In order to make a consumer digital camera small and inexpensive enough, the sensor that is used to gather the light, to produce the image, is very small. As a result, the ultra-small pixels 

Decide what you want to do with the photos you take. If you hardly ever make large prints, save your money and buy something smaller. If you need to make large prints then go for the larger size. If you always email images you can do fine with a small size… 

3 - 4 megapixels
This size is great for 4 x 6 inch photos and the occasional 8 x 10 inch print. It is a good balance between file size and quality. 

5 - 8 megapixels
Once you reach the 5-8 mp range you are looking at larger file sizes and usually superior quality images when enlarged to. 11 x 14 inch and bigger. 

The lingo:The photo-sensitive sensor that receives the image from the lens comes in different types. They are either: either charge-coupled device (CCD) or complementary metal–oxide–semiconductor (CMOS). 

A Pixel is a small element that makes up your sensor. It comes from the words PICture ELment.

A megapixel is 1 million pixels. To calculate the amount of pixels or megapixels take the two measurements of pixels and multiply them.

Resources:

Megapixel calculator