PocketCalcs

Ohm's Law Calculator

Enter any two values to calculate the other two. Leave unknown fields empty.

Ohm's Law Wheel Reference

Voltage (V)

  • V = I x R
  • V = P / I
  • V = sqrt(P x R)

Current (I)

  • I = V / R
  • I = P / V
  • I = sqrt(P / R)

Resistance (R)

  • R = V / I
  • R = P / I^2
  • R = V^2 / P

Power (P)

  • P = I x V
  • P = I^2 x R
  • P = V^2 / R

Frequently Asked Questions

What is Ohm's Law?

Ohm's Law is a fundamental principle in electrical engineering that describes the relationship between voltage, current, and resistance in an electrical circuit. It states that:

  • Voltage (V) equals current (I) multiplied by resistance (R): V = I x R
  • The law was named after German physicist Georg Simon Ohm
  • It applies to most conductive materials under constant temperature
  • It forms the foundation for understanding and designing electrical circuits
How do I use this calculator?

Using this Ohm's Law calculator is simple:

  • Enter any two known values (voltage, current, resistance, or power)
  • Select the appropriate unit for each value (V, mV, kV, A, mA, etc.)
  • Leave the unknown values empty
  • Click "Calculate" to find the missing values
  • The calculator will automatically determine which formulas to use
What is the relationship between power and Ohm's Law?

Power is closely related to Ohm's Law through several formulas:

  • P = I x V (Power equals current times voltage)
  • P = I^2 x R (Power equals current squared times resistance)
  • P = V^2 / R (Power equals voltage squared divided by resistance)
  • These formulas are derived by combining Ohm's Law (V = IR) with the basic power formula
What are common unit prefixes in electrical measurements?

Electrical measurements often use metric prefixes to handle very large or small values:

  • Micro (u): One millionth (10^-6) - e.g., microamps (uA)
  • Milli (m): One thousandth (10^-3) - e.g., millivolts (mV), milliamps (mA)
  • Kilo (k): One thousand (10^3) - e.g., kilovolts (kV), kilohms (kOhm)
  • Mega (M): One million (10^6) - e.g., megohms (MOhm)
Why do I need at least two values?

Ohm's Law equations have three variables, and you need two to solve for the third:

  • With one value alone, there are infinite possible solutions
  • Two values uniquely determine all other electrical properties
  • Some combinations work better than others (e.g., V and I, or V and R)
  • The calculator handles all valid two-value combinations automatically