Print Size vs Resolution

I should probably inject some clarity into my comments below about D7000/D7100 choice, and why you might actually need more resolution.

The accepted rule of thumb for printing for display is 300 points-per-inch, so to determine the 'native' print size from your camera, simply divide it's horizontal and vertical resolution by 300 to give your print size in inches.

Thus the D7100 should be easily good enough for 18"x12" prints. But here's the rub: you can get to this size from a D7000 file by only slightly reducing the resolution to around 250ppi.

Such a reduction will be practically unnoticeable at normal viewing distances - chances are a carefully shot and post-processed D7000 RAW file will compare very well to a D7100 jpeg.

So, if you never print beyond A3, and if you're not already routinely shooting RAW, with good shot discipline and are completely competent in your RAW conversion and processing, then the D7100 is probably more camera than you need.

Which camera?

This is something I get asked all the time, and the single parameter that most people seem to measure digital cameras by is the number of megapixels.

The question to ask is: how big do you want to print? Wassat, you NEVER print? OK, then you need no more than a 2MP image, which will easily fill the average computer screen. Oh, hang on although your images are mainly posted on the web, you occasionally wanted to print A4?

The rule of thumb for commercial printing (magazines, books, etc) is that you need no more than 300 dots per inch (dpi) on the printed page. So for your A4 print, you need around 6 to 8MP, based on a 6MP image being about 3000 pixels wide (3000 pixels divided by 300dpi = 10 inches). That's it, job done!

For detailed comparisons of digital cameras, see here.