How many #12 wires in 1/2and3/4 metal tubing emt.allowed.

It would be different for different conduit types because each different material has it's own ID
Size. Remember to check with your local codes as well.
Here's a link that might help you for this question and more. Designing Conduit Runs -- calculating fill factor, sizing conduits, fill factor, designing conduit runs, electrical metallic tubing, 569 compliance, conduit bends. (http://www.lanshack.com/DesigningConduitRuns.aspx)

You are specific with the conduit type being EMT. Before knowing how many wires can fit in any conduit, the type of insulation must be known, as each insulation has different outside diameters.

The most popular wire now is THHN/THWN, and according to the NEC 2008 Edition Annex C Table C1, 1/2" EMT can take 12-#14 and 9-#12, 3/4" can handle 22-#14 and 16-#12.

While this gives the max wires allowed, this brings up another issue to be concerned with, derating of the ampacity of the current carrying conductors. This can be accomplised by increasing the size of the conductors, which will affect the wire fill of conduit and may require a larger conduit, or using a smaller size fuse or circuit breaker.

As there are many variables and calculations to consider, all the details are needed to be able to size a conduit run. Just because a 3/4" EMT can handle 22 #14 THHN wires, does not mean that all 22 #14 wires can be current carrying and protected with 15 amp breakers.