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Ohms Law Calculator and Tutorial

Enter any two known values, select units and press Submit to solve for the others.
Ohm's Law Formula Chart. Showing the formulas for Resistance, Power, Voltage and Current.

Ohm's Law Explained

Ohm's Law is the relationship of any DC circuit between Voltage, Current and Resistance first discovered by German physicist Georg Ohm. It states that if current is applied across a conductor between two points is directly proportional to the voltage across the two points. Knowing any two values, you will be able to solve for the missing value. A great way to remember the formula is to use Ohms triangle where Voltage is on top and Current and Resistance are on the lower left and right sections.

Ohms Triangle


To Find Voltage
V = I x R

Finding the voltage using the triangle you will need to know the Current (I) and the Resistance (R). Multiple the I X R to find the voltage

Formula: V = I x R
Example: 2A x 20Ω = 40V

To Find Current
I = V / R

Finding the current using the triangle you will need to know the Voltage (V) and the Resistance (R). Divide the V by R to find the current

Formula: I = V / R
Example: 40V / 20Ω = 2A

To Find Resistance
R = V / I

Finding the resistance using the triangle you will need to know the Voltage (V) and the Current (I). Divide the V by I to find the resistance

Formula: R = V / I
Example: 40V / 2A = 20Ω

Commonly the letter (V) is used to represent Voltage, (I) is used to represent Current and (R) is used to represent Resistance.

Electrical Power Explained

Electrical Power (P) or watts is the rate at which energy is absorbed or produced within a circuit. Power is prdouced by many sources such as generators, batteries, solar, wind and other sources. The power is then supplied to homes and businesses. The same principals apply as before. If you know two values you can solve for the others.

Power Triangle


To Find Power
P = I x V

Finding the power using the triangle you will need to know the Current (I) and the Voltage (V). Multiple the I X V to find the power

Formula: P = I x V
Example: 2A x 40V = 80W

To Find Current
I = P / V

Finding the current using the triangle you will need to know the Power (P) and the Voltage (V). Divide the P by V to find the current

Formula: I = P / V
Example: 80W / 40V = 2A

To Find Voltage
V = P / I

Finding the voltage using the triangle you will need to know the Power (V) and the Current (I). Divide the P by I to find the voltage

Formula: V = P / I
Example: 80W / 2A = 40V

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