How to calculate how much energy a circuit wiill use, to find the appropriate battery

I am designing a circuit, which use a micro controller (teensy 3.1), and various sensor.

I am aware of the sensor consumption, since it is in the specs, same for the MC; but these are theoretical values; which does not give you a real figure about how much your circuit will use.

Since I need to power the circuit with a battery, I want to know how to find out the actual consumption when the circuit is working.

Can I just grab the multimeter and measure somehow the energy used? I know the mA that each device takes; but beyond that; I am not sure about how to go for the calculation. Someone suggested me to have the ciruit to run, with a fully charged battery; measure the operation time and then calculate the value based on the capacity of the battery

Example: 1200mAH last for 1h, the circuit use 1200mA; if it last 10h the circuit use 120mA.

This makes sense but I can't believe that this is how professionals actually measure consumption.

• Take the worst case values from datasheets. use them for calculating required time with battery.. – user19579 Nov 12 '15 at 6:24