In article ,
"John Grabowski" wrote:

24 watts divided by 1000 equals .024 KW times 1 hour equals .024 KWH times
10 cents per hour would cost you .0024 cents to operate for one hour. I
think.

Just a nit: You multiplied by 0.1 to get the final answer, which works
for dollars but not cents. So, .0024 dollars/hr, or .24 cents/hr.
Small change either way.

For general electric costs rule-of-thumb, I use the 100W lightbulb, at
$0.10/kWH (common rate in the U.S.), and 1 month (electric bill
frequency), to come up with:

0.1kW * 1 month * 30 days/month * 24 hrs/day * $0.10/kWh ~= $7/mo.

So, $7/mo. to run a 100W device all the time. Most appliances and duty
cycles can be scaled to this benchmark pretty easily.