How to Calculate DC Voltage

By Christopher Donahue; Updated April 24, 2017
Calculating resistances

Through Ohm's law, you can calculate the voltage (V), current (I) and resistance (R) of a DC circuit. From that you can also calculate the power at any point in the circuit.

Follow Ohm's law: Voltage (V) = Current (I) times Resistance (R).

V = I * R

Use this example to calculate DC voltage. If I is 0.5 amps-DC (500 milliamps DC or 500 mADC), and R is 100 ohms:

V = I * R = 0.5 * 100 = 50 volts, or 50 VDC

Calculate power if you know both current and voltage:

Power (watts) = Voltage (volts) * Current (amps) P = V * I

From Step 2:

P = 50 V * 0.5 A = 25 W

Divide DC voltage by 1,000 to express in kilovolts, or KVDC:

17,250 VDC / 1,000 = 17.25 KVDC

Calculate small voltages. It may be more convenient to express the DC voltage in millivolts by multiplying by 1,000:

0.03215 VDC * 1,000 = 32.15 mVDC

About the Author

Chris Donahue is an electrical engineer living in the Dallas area. He has worked on defense projects, semiconductor process equipment, instrumentation and is currently in water utilities. He earned his Registered Massage Therapist (RMT) standing in Texas in 1999.