Calculating resistance (Ohm’s Law)

Ohms law is an important and fundamental rule to remember when working with resistors and electronics in general. It defines the relationship between the components’ current I in amps (A), voltage V in volts (V) and resistance R in ohms (Ω). Ohm’s law consists of three mathematical equations that explain the relationship between current, voltage and resistance. If you know two of these values, you can calculate the third using Ohm’s Law. The three equations are:

I x R = V (current multiplied by resistance = voltage)
V ÷ R = I (voltage Divided by resistance = current)
V ÷ I = R (voltage divided by current = resistance)

Electrical power, measured in watts, can be calculated using Ohm’s law. The power formula is P = V * I. If given voltage and current, this is easy to calculate by plugging in numbers. By substituting Ohm’s formula, power can be calculated with resistance as well.

We have produced a handy online calculator to help with calculating the above formulas as well as other engineering calculators. These are just some of the options: