How do I find out how many physical-qubits I'm using when I run my program in an IBM Q backend quantum computing system?
When you wrote your Qiskit program you had to specify how large your quantum register was or you put qubits in your quantum register as you wrote the program in your code. That's how many qubits you are using. You can also use the len function on the Quantum Register to check it's size. Another way is to print the quantum circuit or call the
draw() function and you will get a picture of the quantum circuit, this will show you how many qubits you are using.