16mp p&s vs 12mp DSLR?

I currently have a 16mp P&s camera, and am planning on upgrade to a 12Mp DSLR… I know Mp doesn't make a big difference, but how much could I blow up a 12mp DSLR photo before seeing a lot of Blur/noise? What print size? Also Advantages and disadvantages of both cameras?

The thing about pixels is that more is in theory, better. In practice, however, more is not always better. The more pixels any sensor has the higher the resolution. However the more pixels a sensor has, the smaller those pixels must be in order for all of them to fit. The smaller the pixels the lower the image quality. I define image quality as color accuracy, dynamic and tonal range, and sharpness due to diffraction (or the lack of).
It's like baking cookies. You can fit 12 cookies onto a baking sheet. If you want to fit 24 cookies onto the same cookie sheet, you have to make the cookies smaller and closer together. So it is with sensors with higher pixel counts. Sure higher pixel counts provides higher resolution, but the smaller pixels can't capture the same amount of light as larger ones can. Therefore you get more noise at any give ISO setting. That's why Sony put out the A7S at only 12MP, the A7R at 36MP. They're designed to produce either images with the lowest possible noise at high ISOs, or the highest resolution at 36MP on the A7R. The only way to get both is to use an even larger sensor with enough room to use big pixels and a lot of them - that's where the medium format Pentax 645D or 645Z, or the Hasselblad H5D come into play. They've got a sensor that's 70% larger than a full frame camera allowing for big pixels and a lot of them too.
So to make a short answer long, don't put any weight into pixels when comparing two different sensors. You may actually see an increase in details with the DSLR at a lower pixel count because of the lens quality found on DSLRs vs those on p&s. But you're sure to get better image quality and versatility with any DSLR over any P&S.

To double the linear resolution you need to quadruple the megapixel count. So in real world usage you're not going to notice the difference in resolution between a 12mp DSLR and a 16mp example, assuming the lenses are of similar quality.

I used to make perfectly good A4 prints from my old 2mp Nikon point & shoot, when I moved to a 5mp Sony I was able to make slight selective enlargements but it was only when I upgraded to an 8mp Konica-Minolta model that I could make useful crops. But to be able to double the enlargement possible on my 2mp model, I'd need a 16mp camera.

Megapixel counts are driven by marketing and not be necessity.

Picture quality deterioration will approximately start beyond 10x15" (300DPI).

Since even a 6 mp sensored digital SLR will out perform a 16 mp P&S camera, you will find that the 12 mp dSLR will be able to produce far superior images.

How far can you enlarge a full resolution image from a 12 mp dSLR? I have made some 3x4 foot images with no problem, however when enlarging image files to such sizes, you have to increase the depth of field of the image when you shoot it, since the larger the image becomes, the more the out of focus areas of the print start to show up.

Noise has more to do with the ISO you are using and how well the cameras sensor performs at those ISO settings. For instance the 12 mp Nikon D3s can produce nearly noiseless images at 6400 ISO (or even 12,800 if the image is used on a website) while my Nikon D300 starts to show noise once it gets beyond 3200 ISO.

The advantage of a dSLR should be obvious. It uses interchangeable lenses and is fully adjustable. Size is the only consideration some people think is important, but since a camera is just a tool, you tend to buy the tool you need for your specific job.

If you mean the Canon T3, well the fact that it is 12 MP means little compared to competing models that have more megapixels. It is shy on features that you might miss. The T3i, besides 18 MP which is least important, has dust reduction, more autofocus sensors and better ones, video autofocus, articulating LCD, and outlet for an external microphone.

There are printing methods and then there are printing methods. Without using interpolation, 12MP will easily blow up to 15"x12". With interpolation, how does billboard size work for you?
http://digitalphotographylive.com/megapixels-vs-print-size/

They still make 12mp DSLR? Must be an old one or something, all the new ones have atleast 20mp