I noticed that alot of people wonder if it is worth upgrading, for example, to an 8 mp camera froma 4 mp camera on megapixels alone. Now there are normally other factors involved too such as lens quality, sensor size, noise, speed, features, and such that also should be considered when deciding if one should upgrade his or her camera. But regarding MPs alone I have created a tool to help in this regard at http://mattspinelli.com/mpcalc.html
Lets say the 4mp camera someone might have is a 4:3 ratio but they were wondering how much more resolution the 8mp camera would have compared to it. But wait, the 8mp is a 3:2 aspect ratio. How much overall resolution gain would there be? What about vertical and horizontal gain? How much larger would it print?
If 8 mps has 2 times as many pixels as 4 mps would it print twice as large? Would it have twice the resoultion? These are things that I notice people thinking so I thought I would help them out. Here is the results from using the calculator with the above example (camera #1 is 4mp and camera #2 is 8mp):
Approximate Image Size:
Camera #1 ~ 2309 x 1732
Camera #2 ~ 3464 x 2309 (2x the pixels of camera #1)
Camera #2 has 41.4% more overall resolution than camera #1
Camera #2 has 50% more horizontal resolution than camera #1
Camera #2 has 33.3% more vertical resolution than camera #1
What does this mean?
At 300PPI the two cameras would make the following 3:2 and 4:3 sizes:
Camera #2 would print at 7.7" x 11.55" whereas Camera #1 at 5.13" x 7.7"
Camera #2 would print at 7.7" x 10.26" whereas Camera #1 at 5.77" x 7.7"
that this comparison assumes that image quality (lens quality, noise, etc) is comparable for both cameras.
Hope this is useful to you guys. Enjoy!