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Forget about r=e/i. A simple formula that will work for you is the power equation. Power = current x voltage. If you want to figure current draw, you can transpose the equation to current ( the amperage drwn through your ckt breaker ) by using:
amps drawn through circuit = total (sum) of all the bulbs wattage in your display divided by 120 volts (you household voltage). P.S. Hate to pay your electric bill if you are tripping a 30 amp breaker on Christmas lights! Try splitting them up on separate extension cords plugged into different outlets (breakers). Check wiring of lights for frayed insulation/shorts.
amps drawn through circuit = total (sum) of all the bulbs wattage in your display divided by 120 volts (you household voltage). P.S. Hate to pay your electric bill if you are tripping a 30 amp breaker on Christmas lights! Try splitting them up on separate extension cords plugged into different outlets (breakers). Check wiring of lights for frayed insulation/shorts.
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They are not the same thing. Your outlets are 120 volt. They are protected by a fuse or a circuit breaker that will let 15, 20, or 30 amps of current flow from that outlet before it shuts down (depends on what is really in your house  look at the fusebox or breaker panel for the number).
If there are two places to put a plug into and they are both on the same circuit you can not just add up the current and think you can do twice as much. If that is a 15 amp circuit you don't get two times 15 if you use both sockets.
As far as watts they are power and are arithmetically the answer you get if you multiply the voltage (=120 volts) times the current (up to maybe 15 amps).
For example if you used a 15 amp circuit the arithmetic says 1800 watts. But what else is on the circuit using up some power. If you have a 1000 watt broiler on it there is only 800 left for decorations for example. 
Screw volts. If you are talking about house wiring, then use 120 volts.
Watts roughly equals volts times amps. I say roughly because it gets more complicated for things like motors. But for lamps it is OK. If you have a 1 amp lamp, then it is using 120 watts. Roughly.
Since lamps usually aren't rated in amps, you have to go the other way. Amps equals watts divided by volts. Roughly. So, if you have a 100 watt light bulb on a 120 volt circuit, you are pulling a little over .8 amps. Roughly.
Two 100 watt bulbs? Then it would be roughly twice that amount. And so on.
I keep saying roughly because of other factors. Lamps draw a lot more current (amps) at turnon than they do while running. 

V = W/A
voltage is like water pressure
amperage is like water flow
ohms is resistance
current equals voltage divided by resistance 
watt = volt x ampere p.s. Meglio che consulti Wikipedia

USE OHM;s Law to figure it out.
or one of these other fomulasSource(s):

4 answers hidden
HOw many Volts are in 1 AMP?
I don't know anything about Volts, Watts, or Amps. Which i should because i put up a HUGE Christmas Display every year. I started Decorating this year and i already blew one curcuit >spelling<. I moved the source to my deck outlets which are 30 AMPS combined (there are two outlets on the deck). so basically i can do the math if i have the numbers.
So whats order does it go in
Ex. How many watts are in a volt,
How many volts are in an amp?
Thank you so much for whom ever helps me out with this. I'll be sure to give you your ten points.
So whats order does it go in
Ex. How many watts are in a volt,
How many volts are in an amp?
Thank you so much for whom ever helps me out with this. I'll be sure to give you your ten points.
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