Ohm's Law Calculator

Electromagnetism & Circuit Theory

Formulated by German physicist Georg Simon Ohm in 1827, Ohm's Law states that the current flowing through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance.

The 12 Ohm's Law Wheel Equations

• Solving for Voltage (V):

• V = I × R

• V = (P) / (I)

• V = √(P × R)

• Solving for Current (I):

• I = (V) / (R)

• I = (P) / (V)

• I = √((P) / (R))

• Solving for Resistance (R):

• R = (V) / (I)

• R = (V^2) / (P)

• R = (P) / (I^2)

• Solving for Power (P):

• P = V × I

• P = I^2 × R

• P = (V^2) / (R)

Practical Electrical System Sizing

Electricians and HVAC technicians utilize Ohm's Law wheel calculations when sizing wire cross-sectional gauge area and branch circuit breakers, preventing electrical overheating and fire hazards in residential and industrial installations.

Alternating Current (AC) Impedance Extension

In AC circuits, Ohm's Law expands to vector phasor form, replacing pure resistance with complex impedance to account for inductive reactance and capacitive phase shifts.

How to Use This Calculator

Enter your Known Values Pair — choose from Voltage (V) & Current (I), Voltage (V) & Resistance (R), Current (I) & Resistance (R), First Input Value (e.g. 120), and Second Input Value (e.g. 10). Verify your units match the formula standard (SI vs imperial) before entering values.

The Formula

Formula Reference: Ohm's Law Calculator

Input variables:

knownPairMode — Known Values Pair

val1 — First Input Value

val2 — Second Input Value

Computed outputs:

voltageVoltsV — Voltage (V)

currentAmpsI — Current (I)

resistanceOhmsR — Resistance (R)

powerWattsP — Power (P)

Mathematical relationships extracted from calculation logic:

P = safeDiv(V * V, R)

R = safeDiv(V * V, P)

V = Math.sqrt(P * R)

Standard: NIST CODATA physical constants and SI unit conventions

Worked Example

Calculating circuit parameters for a 120.0 V appliance drawing 10.0 A of current: Yields 12.000 Ω circuit resistance and 1,200.00 Watts of electrical power.

Understanding Your Result

Scientific calculations require careful attention to significant figures and units. Your result is only as precise as your least precise input — expressing the result with more significant figures than the inputs implies false precision. For laboratory or regulatory work, verify which measurement standard applies (SI, ASTM, ISO) and whether temperature, pressure, or concentration conditions affect the formula. Cross-reference results against published reference values for your specific material or compound.