Re: How can I tell how much heat a microwave gives off?

Microwave does not give off the heat.  The energy is transmitted from the
Magnetron located usually on the side or top of the MW, in the form of
microwaves which make the water molecules in food oscillate very fast and
produce heat by friction.  There are ways to measure MW enery transfer,
loss and absorption but they not easy.

-MVK

[Moderator Note:  One simple minded approach you might try is to boil a measured 
quantity of water in the microwave in a measured amount of time.  To boil a gram 
of water takes a definite amount of energy, so you can convert the amount of 
water lost to boiling into energy absorbed by the water.  Divide the energy by 
the time to get a estimate of the power output of the microwave.  There are many 
variables that would affect the accuracy of your result which I am not 
mentioning.  It might be interesting to see how consistent this method is with 
one oven, or to compare two different