How to Calculate Milliamps

By Christopher Donahue; Updated April 24, 2017
Calculate Shunt Resistors

Ohm's Law is the basic formula for electronics. With it, we may calculate Resistance (Ohms), Voltage (Volts) or Current (Amps) by knowing any two of the three values.

How to Calculate Milliamps

A milliamp is one one-thousandth of an amp. By calculating the value in amps and dividing by one thousand, you will have a value of current in milliamps.

Ohm's Law is Voltage = Resistance X Current. The derivations are: Resistance = Voltage / Current Current = Voltage / Resistance

Calculate Current using your known Voltage and Resistance as shown in Step 2. Current (I) = Voltage (V) divided by Resistance (R) I = V/R Ex: if your voltage is 12V and resistance is 200 Ohms I = V/R = 12 / 200 = 0.06 Amps

Knowing your Current in Amps, multiply by 1000 to see the value in milliamps Ex: 0.06 Amps x 1000 = 60 milliamps

Given a known Voltage and Current, you may also derive Power (Watts). Power = Voltage times Current ( P = V x I ) Ex: 12V x 0.06A = 0.72W or 720 milliwatts

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.