Help me calculate the total voltage loss of circuit - DC
You have five circuits so you want to calculate the voltage loss in each individual circuit not "the total voltage loss in my circuit".

2.5 mm² copper has a resistance of 7.50 mΩ/m. You have your lengths (but don't forget to double the lengths to include the return leg). Now you can work out R for each circuit.

You already have I so V = IR will get you the voltage drop.