How many watts does a motherboard use?

Answer 1

It varies from motherboard to motherboard. Motherboards with higher clocked RAM will tend to need higher watts and motherboards will older cpus or some of the newer quad cores will take even more watts.

Answer 2

with a CPU consuming around 100 watt, and 1333mhz memory @ 1.5-1.6 volt, I would at least estimate 200 watt on the mobo.

It depends if you have fans connected to the motherboard or not as well.

also, if you overclock you can quickly bypass 200watt only on the cpu (often with AMD processors bypassing 4.4 ghz and core voltages above 1.5