Megapixels are important because the greater the number of megapixels, the larger the photograph can be printed with good results.

Most ink jet printers can print good images at 200 or 300 ppi (pixels per inch) which is the rough equivalent of 100 to 150 dpi (dots per inch). There are more pixels per inch because there is no space between the pixels. (On a printed page, however, there is space between the dots, so the number of dots per inch is lower than the number of pixels per inch).

Many digital cameras today have at least six megapixels. That means that you can get close to perfect resolution when printing an 8" by 10" photograph at 300 ppi or 150 dpi. The same 6-megapixel photograph will give you excellent results when printed as large as 10” by 15” print at 200 ppi or 100 dpi.

Often perfect resolution is not even necessary because to the average eye a large 4-megapixel print will look as good as a similar-sized 6-megapixel print.

Most photographs are printed at 3” by 5” or 4” by 6” and most ink jet printers can only accept paper as large as 8 ½” by 11”. So a 6-megapixel camera will be more than adequate for most average computer users.

This chart will give you an idea of how many megapixels are needed for a good quality print, printing at 200 ppi. The pixel image size for the listed megapixels will differ slightly with different cameras.

If you print at 150 ppi, you will get a lesser quality, but often acceptable prints in larger sizes. True photo quality prints will be printed at 300 ppi.

To determine exactly the size prints that the megapixels will support, find the pixel resolution image size and divide each dimension by the number of pixels per inch for the print. For example, the 6-megapixel image size from the above table is listed at 3008 x 2000. To get the largest print size of good quality (200 ppi) divide each dimension by 200 which will give you 15.04” x 10”. If you will print at 150 ppi, divide each dimension by 150 which will give you a maximum print size of 20.05” x13.34”. If you want photo quality prints printed at 300 ppi, divide each dimension by 300 which results in 10.03” x 6.67”.

If you only want to print photographs up to 4” by 6”, a 3-megapixel camera would suffice. Yet, there may be times when you may want to blow up a portion of the photo to print it. In that case you will need a camera with a higher resolution so that when you blow up that area, it will still have enough resolution to print well.

If you want to get a detail from a picture, you need to get a picture in high resolution to be able to crop the detail out of the picture (I hope you get the idea by just reading this).

Also be aware that you don't need a high megapixel count to show pictures on a computer monitor. Most monitors have resolution of 1024 x 768" or 1280 x 900. As you can see from the chart above, a 3-megapixel image will look fine on a computer monitor with these resolutions. So you don't need a high-megapixel count for putting images on the Web or on a computer screen.

One more thing to be aware of, the higher the resolution of the picture, the larger the file and the more space it will take up on the media card. Most cameras allow you to take images of different quality. The adjustments usually say something like low, medium, or high quality. Some people use the lower quality to save space on the memory card. Then they find that when they decide to print a large photo, it is grainy or blurry. If you don't know how large you will want to print your pictures, it is best to get a media card with a large capacity and to take your photos at a high quality.