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Ohm's Law Calculator

What this calculator does

The Ohm's Law Calculator provides fast estimates using standard electrical relationships. Enter Voltage (V) - Volts, Current (I) - Amps, Resistance (R) - Ohms to compute results for real-world electrical scenarios. Use it for quick checks, comparisons, and documentation while planning.

Inputs explained

  • Voltage (V) - Volts: Electrical potential difference in volts (V).
  • Current (I) - Amps: Electrical current in amperes (A).
  • Resistance (R) - Ohms: Resistance in ohms (ohm).
  • Power (P) - Watts: Power value as labeled (W, kW, VA, or kVA).

How it works / Method

The calculator applies the listed formulas to the values you enter and then formats the result in standard units.

Formulas used

  • V = I x R
  • I = V / R
  • R = V / I
  • P = V x I
  • Volts x Amps
  • Amps² x Ohms
  • Volts² / Ohms

Units: V in volts (V) I in amperes (A) R in ohms (ohm) P in watts (W)

Ω

Calculator Tool

Calculate V, I, R, and P - Enter any two values

V
A
Ω
W

Enter at least 2 values to calculate the others

Results
Enter 2+ values

Ohm's Law Formulas

Voltage V = I × R
Current I = V ÷ R
Resistance R = V ÷ I
Power P = V × I

Power Formulas

P = V×I Volts × Amps
P = I²R Amps² × Ohms
P = V²/R Volts² ÷ Ohms

Related Calculators

Watts to Amps Volts to Amps Voltage Divider

Step-by-step example

Scenario: Find current through a 100Ω resistor with 12V applied.

Formula: I = V / R

  1. I = 12 / 100
  2. I = 0.12 Amps (120 mA)

Result: 0.12 Amps (120 mA)

Use cases

  • Solve for voltage, current, resistance, or power quickly.
  • Check resistor sizing and expected drops.
  • Validate lab measurements against theory.
  • Create quick references for basic circuit work.

Assumptions & limitations

  • Results are estimates and may be rounded; small differences are expected.
  • Inputs assume steady-state values; transient and surge effects are not modeled.
  • Voltage can vary by supply, load, and location; use measured values when possible.
  • Power factor varies by load type; use a realistic value for inductive equipment.
  • Wiring rules and safety codes vary by jurisdiction; consult a licensed electrician for installation decisions.

Sources & references

Related calculators

Frequently Asked Questions

The Ohm's Law Calculator solves for voltage, current, resistance, or power. Provide any two values and it returns the remaining result. It is useful for quick checks in labs and troubleshooting. Use it for basic circuit estimates. Assumes ideal resistive conditions unless otherwise noted. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

Ohm's law uses V = I x R. Power relationships include P = V x I, P = I^2 x R, and P = V^2 / R. These equations apply to resistive circuits. Use consistent units for accurate results. Convert milli or kilo units before calculating. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

The equations are exact for DC and resistive AC circuits. AC circuits with reactance use impedance instead of resistance. Phase angle changes real power. Use AC analysis for inductive or capacitive loads. This tool is best for basic estimates. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

Accuracy depends on your inputs and component tolerances. Temperature and measurement error can affect results. The calculator assumes ideal conditions. Use measurement to verify critical values. Add safety margin for power ratings. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

You can estimate power dissipation and choose a wattage. Always add margin for heat and tolerance. Check datasheets for voltage and temperature limits. Use appropriate safety practices for high power. Consult a professional for safety-critical designs. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

Use volts for V, amperes for I, ohms for R, and watts for P. Convert milliamps and kilovolts to base units. Keep units consistent across all inputs. The calculator expects base units unless labeled otherwise. Check units on the input fields before calculating. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.