Hello, I have bought a house that was gutted do to a fire, the house was built in 1967 (Texas) all of the wiring in the house is aluminum, since 1/3 of the wiring was damaged in the fire I won't to replace all the wiring with copper wire. I will run #15 wire for all lights, #20 wire for outlets (living, hall,4-bedrooms). How do I calculate how many lights to a #15 and how many outlets to #20. I have been told 7 to 8 outlets on #20 and 10 to 12 lights on #15. In the kitchen I was planning on running #20 to refrigerator and one outlet, #20 to stove (gas) and microwave, #20 to dishwasher, garbage disposer and 3-counter top outlets.
Thank you in advance for all your insight.

I take it you mean 12 gauge wire which handles 20 amps, and 14 gauge wire which will handle 15 amps.
The Kitchen recepticles are 2 to a circuit and need to be GFI protected. If money is not real tight, I wouldn't use #14 gauge wire. #12 for everything, except for the large loads, A/C Range Dryer Etc.

Tks
For living room and bedrooms what is a good rule of thumb for how many recepticles to one circuit?

In residential wiring, there is no limit on the allowable receptacles.

However common sense does limit what you install.

For example, a 15 amp / 120 VAC circuit will allow up to 1800 Watts.

If for example you wanted to supply power for a 1700 Watt device you would be fine using this circuit as a independent or dedicated circuit.

However, if you are planning on supplying more than one outlet you are limited to 80% of the 1800 Watts or 1800 X .8 = 1440 Watts.

So you would figure out how many outlets you want to use and the number of watts used per outlet to get a circuit total.

For example, 1400 / 60 (sixty watt lamps) = 24. If however you wanted to use 150 watt lamps, then it would be 10.

The math applies to a 20 amp circuit.

With respect to the kitchen, there must be two 20 amp branch circuits to supply the kitchen counter top receptacles and both must have GFCI protection.

There is a very good book on Residential Wiring by Ray Mullin that shows you how to do the worked based on the 2008 NEC. I do not know if he has released a 2011 book yet.