Calculation sequence
Step-by-step method
- Select the unknown quantity.
- Enter the two required known quantities.
- Rearrange V = IR, then calculate resistive power from P = VI.
ElectricalBeginnerElectrical Fundamentals
Ohm’s Law Calculator
Solve the basic resistive relationship among voltage, current, resistance, and power.
Why it matters: Ohm’s law is the foundation for checking DC and simple resistive circuits, sensors, heaters, and control wiring.
Calculated result
Engineering evaluation
Calculated current (I)10 A
- Voltage (V)
- 120 V
- Current (I)
- 10 A
- Resistance (R)
- 12 Ω
- DC/resistive power (P)
- 1,200 W
Engineering interpretation
The calculated current is 10 A. For AC circuits with reactance or non-unity power factor, use the appropriate impedance and AC power relationships instead.
Engineering knowledge center
Understand the calculation—not just the answer
Governing relationships
V = I × R
P = V × I
Current substitution
V = 10 A × 12 Ω = 120 V; P = 120 × 10 = 1200 W.
Equation legend
Inputs and calculated quantities
- V
- Voltage — V
- I
- Current — A
- R
- Resistance — Ω
- I
- Calculated current — A
- V
- Voltage — V
- I
- Current — A
- R
- Resistance — Ω
- P
- DC/resistive power — W
Applications
How this calculation is used
Building design
Perform basic circuit and component checks.
Construction
Evaluate measured voltage, current, and resistance for simple resistive loads.
Commissioning
Check sensor circuits, electric heaters, and control components while respecting isolation and safety requirements.
Quality controls
Assumptions and limitations
Assumptions
- DC or purely resistive steady-state circuit.
- Entered measurements are RMS-equivalent where applicable.
Limitations
- Does not model reactance, phase angle, harmonics, inrush, or temperature-dependent resistance.
- Does not establish conductor size, protective-device rating, safe work condition, or code compliance.
Field use
Verification procedure
- Follow the approved electrical-safety procedure.
- De-energize and verify absence of voltage before resistance measurement.
- Use correctly rated calibrated instruments.
- Compare with nameplate and manufacturer data.
Common engineering mistakes
- Measuring resistance on an energized circuit.
- Applying the result directly to reactive AC loads.
- Ignoring meter burden and lead resistance.
Technical basis
References and source standards
- NIST Reference on Constants, Units, and UncertaintySI electrical units and quantity conventions.
Engineering calculation disclaimer
These engineering tools are provided for educational, preliminary evaluation, field verification, and commissioning support. Results depend on the accuracy of user-entered information and the assumptions stated for each calculation. Every colored status and comparison is a screening indicator only; project criteria, contract requirements, applicable codes, manufacturer instructions, measurement uncertainty, and authorized engineering judgment govern. The tools do not replace project-specific engineering analysis or the judgment of a licensed professional engineer.
Read the full use and limitation statement