Ohm's Law Calculations With Power

In the four tables below, you may enter two of the four factors in Ohm's Law. They are Power (P) or (W), measured in Watts, Voltage (V) or (E), measured in Volts, Current or Amperage (I), measured in Amps (Amperes), and Resistance (R) measured in Ohms. The needed factor will be calculated for you when you click on the Calculate button for that table.

Though not part of the original theory, in later years, we have also attributed the Power factor to Ohm as well. Power is usually abbreviated by (W) and measured in Watts. The formula generally given for Power is:
W = V x I or W = I2 x R or W = V2 / R. Other basic formulae involving Power are:
I = W / V or I = (W / R)2
V = (W x R)2 or V = W / I
R = V2 / W or R = W / I2
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Ohm's Law Factors With Power

Calculate Watts


To calculate the circuit power...
The formula is W = V x I or,
W = I2 x R or,
W = V2 / R

Enter any two factors of V, I, and R


Voltage      Current      Resistance








Calculated Power

Calculate Amperes


To calculate the circuit amperage...
The formula is I = V / R or,
I = W / V or,
I = (W / R)2

Enter any two factors of V, W, and R


Voltage      Power        Resistance

Is it 3-Phase? (Do not enter R if circuit is 3-Phase.)




Calculated Amperage


Calculate Volts


To calculate the circuit voltage...
The formula is V = I x R or,
V = (W x R)2 or,
V = W / I

Enter any two factors of W, I, and R


Power         Current      Resistance




Calculated Voltage


Calculate Ohms


To calculate the circuit resistance...
The formula is R = V / A
R = V2 / W or,
R = W / I2

Enter any two factors of V, I, and W


Voltage      Current       Power       




Calculated Resistance


Resistivity (W-cm) for Common Metals at Room Temperature
Aluminum 2.828 x 10-6
Copper 1.676 x 10-6
Silver 1.586 x 10-6
Gold 2.214 x 10-6
Tungsten 5.510 x 10-6

For example, a 10 Gauge wire is 2.588mm in diameter.
The resistance per cm of copper wire that thick is
3.186 x 10-5W/cm. A mile of this wire has a resistance of 5.13 W.