I have a 100 amp switchbox.The left side has 6 slots ( 1 double switch 20amp, 1 double bar 30amp and 2 single 20amp. The right side has 3 double switch midgets at 20amps and 2 single 20amps. My question is how much can my box take and how do I calculate the usage?

The amount and size breakers in a panel means nothing.

Need to know the square footage of all livable space, including basement if it can be finished, no garage, porch. And list of all major stationary electric appliances, size of any electric heat, AC, and we can do the calcs for you.

Or you can review Article 220 of the National Electric Code, see sticky at beginning of this forum. Read that a few times you will understand why electricians are like they are.

I(E)=P
100(240)=24000W
-A 100A service will supply=24,000 watts

how do I calculate the usage?
If you are trying to calculate the "total work" done. Then you would Multiply watts by total time during which the work (watts) is done.

Example: if a 60w bulb burns for two hours, then: 60w(2)=120 watt-hours. If trying to get total power consumed, then larger numbers will result. Example: Kilowatt-hours

Note: Check with your POCO for calculation methods. You can get the amount of power used per month off your utility bill.

Let me confuse you a bit. 100 A means you have 100 A of 240 V available or 200 A of 120 V available if they were exclusive. I'm probably going to get in trouble for saying it this way.

The breakers have a distribution like every other one is on a different leg, so the way breakers are distributed could cause the main to pop.

Not sure why your asking the question.

A "load calculation" basically determines the service you need for a house.

With a 100 A service a hot tub is not recommended to be installed for example.

Panels are rated by the number of poles that they can accept. A pole can be thought of as the number of wires. This also can exceed the number of slots.

100 A means you have 100 A of 240 V available or 200 A of 120 V available I'll pass on making a big deal out of how you said it, and simply show this to clear "some" smoke for the reader:
100A(240v)=24000w
200A(120v)=24000w

Watt

Watt - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Watt)

I really am not following this line of answers. Seem to be off topic.

I am zoning in on the original question:

My question is how much can my box take and how do I calculate the usage?

Which means a Service Load Calculation will answer the question, once Derrick provides the information I requested.

I really am not following this line of answers. Seem to be off topic.

I am zoning in on the original question:

My question is how much can my box take and how do I calculate the usage?

Which means a Service Load Calculation will answer the question, once Derrick provides the information I requested.
The op said: how do I calculate usage, so I take this as: How much power do I consume in a given period. Yet, the OP titled his question: Load Calculation
:confused::confused:

Watt

Watt - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Watt)
Thank you! Unfortunately I'm well aware of James. :D :)