Ohm's Law Calculator
This Ohm's Law Calculator helps you calculate voltage, current, resistance, and power in a DC circuit. Enter any two known values, choose the units, and calculate the missing electrical parameters.
It is useful for hardware engineers, electronics students, technicians, PCB designers, and makers who need quick circuit parameter checks during design or troubleshooting.
Use it when checking resistor current, estimating power dissipation, validating a bench measurement, or confirming that a component rating is suitable for the circuit.
Ohm's Law Calculator
Enter any two known positive values. The calculator solves the remaining voltage, current, resistance, and power values.
Circuit voltage or voltage across the component.
Use the current flowing through the resistor or load.
Resistance of the load or resistor.
Power dissipated by the circuit element.
Leave unknown values blank for the clearest result.
- Voltage
- 12V
- Current
- 0.02A
- Resistance
- 600Ω
- Power
- 0.24W
Formulas used: R = V / I, P = V x I
Ohm's Law Formulas
V = I × RP = V × IP = I² × RP = V² / R- V = Voltage in volts
- I = Current in amperes
- R = Resistance in ohms
- P = Power in watts
Parameter Explanation
Voltage
Voltage is the electric potential difference across a component or circuit section.
Current
Current is the flow of charge through the component. Use amperes as the base unit.
Resistance
Resistance limits current flow and is measured in ohms. Resistor tolerance can change the real value.
Power
Power is the heat energy dissipated by the component. It is measured in watts.
Worked Example
Example: a 12 V circuit drives current through a 600 ohm resistor.
I = V / R = 12 / 600 = 0.02 A
P = V × I = 12 × 0.02 = 0.24 W
A practical design would usually choose a resistor power rating above the calculated value, such as 0.5 W, depending on temperature and reliability margin.
Engineering Notes
- Choose a resistor with enough power rating and thermal margin.
- Account for resistor tolerance, temperature coefficient, and airflow.
- Use standard component values when selecting real resistors.
- Verify circuit assumptions with datasheets, simulation, and measurement.
Common Mistakes
- Mixing milliamps and amps without converting units.
- Ignoring power dissipation after calculating resistance.
- Using ideal calculated values without checking standard resistor values.
- Forgetting that AC circuits may require impedance calculations.
FAQ
What is Ohm's Law used for?
Ohm's Law is used to calculate the relationship between voltage, current, and resistance in a circuit.
How do I calculate resistor power?
Use P = V × I, P = I² × R, or P = V² / R depending on which values you know.
Can this calculator be used for AC circuits?
It is intended for DC and simple resistive calculations. AC circuits with reactance need impedance-based analysis.
Why should I check power dissipation?
A resistor or load must be rated above the expected power dissipation to avoid overheating and reliability problems.
Reference Links
Continue with the resistor calculators category or visit the engineering reference section as more reference tables are added.
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Disclaimer
This calculator provides theoretical results for reference. Always verify your design with datasheets, simulation, and real circuit testing before production use.