When you are out to buy a Digital Camera (point and shoot or a SLR: Single Lens Reflex) you would consider the cameras resolution in Megapixel right? Well this decision is mainly driven by one factor i.e. the max photo quality image you can print.
So how do I determine the highest quality image that I can print with my megapixel camera?
It’s very simple first get the resolution in pixels of your megapixel camera for e.g. if you own a 4mp camera then your pixel resolution typically will be : 2464 x 1632
For print size divide the resolution (height and width) by 300 (300 is the pixel per inch or ppi resolution required for photo quality - prints, magazines and books).
So you can print a good 8“ x 5“ with your 4mp camera.
There you go if you know your pixel resolution then you can calculate your print sizes.
Does a higher megapixel camera offer better resolution pictures? The answer is obviously “Yes”.
How better? If you purchase a 8 Megapixel camera against a 4 Mepapixel camera can you get photo quality prints of double the print size of a 4mp camera? The answer is “No”
Why?
It's plain and simple: to double the resolution of your print size you need to double the pixel dimensions on both the horizontal and vertical side thus multiplying the existing resolution by a factor of 4 rather than 2.
So if your 4.0 Megapixel camera can print pictures of max size of 8 x 5 then to print 16 x 10 size you need a 16.0 Megapixel camera but NOT a 8.0 Megapixel camera.
Be clear of this “Megapixel Multiplier rule” when buying digital cameras.