How much does it cost to keep my 13" macbook pro plugged in in sleep mode

It is nowhere near a few cents.

I measured the actual power consumption of an 85 W charger for a 17" MacBook Pro. After the MBP is fully charged the charger consumes 1.2 W in standby.

At a cost of 15¢ / kWh this is 0.018¢ / hour * eight hours (overnight) = 0.144¢. It would take a week to spend one cent even at 15¢ / kWh, which is a high estimate.

I did not measure the power while it is charging the MBP; it was already fully charged.

About a dollar 3 eighty.

What are the kilowatt rates in your area? How long is overnight?

Have you tried shutting down overnight for 1 month and then letting it sleep overnight for 1 month and comparing the difference in usage? If you have nothing else to do with your time try it.

Not more than a few cents. If that's a concern to you, I would suggest selling your Mac and purchasing a much cheaper computer.

John Galt wrote:

. . .

I measured the actual power consumption of an 85 W charger for a 17" MacBook Pro. After the MBP is fully charged the charger consumes 1.2 W in standby.

Yup, that agrees with Apple's specs: http://images.apple.com/environment/reports/docs/13inch_macbookpro_per_june2012. pdf