How many watts can be in use on a 15 amp circuit?

15 X .8 = 12 Amps 15 Amps X 80% = 12 Amps(Can't use Full 15 amps)

Volts X Amps = Watts 120 X 12 = 1440 watts

1440/60 = 24 24- 60 Watt Bulbs consume 1440 watts and draws 12
amps

Yes, very helpful... thank you

I see I was lacking some commas, The Formulas will help you forever.
Just remember "Volts Times Amps Equals Watts". Repeat it a couple of times.
Then you can multiply or divide which ever you need to.