Physics
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Ohm's Law Calculator.
Calculate voltage, current, resistance, and power
Set your values
Results update as you type.
Results update automatically after you enter values.
How to Use
V = I × R · P = V × I
Enter any two of voltage, current, and resistance. Supplying all three checks their consistency.
Ideal DC relationship only; real circuits can include frequency, temperature, and component tolerances.
How to Use Ohm's Law Calculator
Ohm's Law is fundamental to electrical engineering and describes the relationship between voltage, current, resistance, and power. This calculator solves Ohm's Law and power equations instantly.
- Calculate voltage from current and resistance.
- Find current given voltage and resistance.
- Determine resistance from voltage and current.
- Calculate electrical power consumption.
- Analyze circuit behavior and efficiency.
Ohm's Law & Power Formulas
Understanding electrical relationships helps you design circuits, troubleshoot problems, and ensure safe operation.
Ohm's Law
Voltage equals current multiplied by resistance.
Example:
Input: Current: 2 Amps, Resistance: 10 Ohms
Calculation: 2 × 10
Result: 20 Volts
Current
Current equals voltage divided by resistance.
Example:
Input: Voltage: 120V, Resistance: 12Ω
Calculation: 120 ÷ 12
Result: 10 Amps
Resistance
Resistance equals voltage divided by current.
Example:
Input: Voltage: 48V, Current: 4A
Calculation: 48 ÷ 4
Result: 12 Ohms
Power
Power is the rate of energy consumption in watts.
Example:
Input: Using P = V × I: Voltage 120V, Current 10A
Calculation: 120 × 10
Result: 1200 Watts
Real-World Use Cases
Ohm's Law is used daily by electricians, engineers, and hobbyists working with electrical circuits and systems.
Home Electrical Safety
Check if your circuit breakers are properly sized and prevent overloads that could cause fires.
LED and Resistor Selection
Calculate the correct resistor values to limit current and protect LEDs in electronic projects.
Power Consumption Calculation
Determine how much electricity appliances use to estimate monthly electric bills.
Circuit Design & Troubleshooting
Verify circuit calculations during design phase and diagnose problems in existing circuits.
Industrial Motor Analysis
Calculate motor specifications, efficiency, and power requirements for industrial applications.
Tips & Best Practices
Tips
- Remember: V = IR (Voltage equals current times resistance).
- Resistance increases with wire length and decreases with larger wire diameter.
- Power dissipation as heat increases with resistance and current.
- Use appropriate wire gauge to handle current without dangerous heat generation.
- Insulators have very high resistance; conductors have very low resistance.
Common Mistakes to Avoid
- Forgetting that resistance changes with temperature in many materials.
- Not accounting for voltage drop across long wire runs.
- Confusing AC and DC calculations - Ohm's Law applies to DC and AC RMS values.
- Ignoring power ratings and causing component overheating or failure.
Related Calculators
Cite this calculator
Canonical URL: https://mathify.one/en/physics/ohms-law
Cite as: Mathify. (2026). Ohm's Law Calculator. https://mathify.one/en/physics/ohms-law
Use Cases
Circuit Design and Troubleshooting
Quickly determine the required resistance or voltage for a given current in electronic circuits, or verify component values during troubleshooting.
Example: Find the resistance needed to limit current to 20 mA with a 9V supply.
Educational Learning and Homework
Check your answers for physics or electronics homework problems involving voltage, current, resistance, and power.
Example: Verify that a 12V battery with a 4Ω resistor produces 3A of current.
Frequently Asked Questions
- What is Ohm's Law?
- Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points, and inversely proportional to the resistance. It is expressed as V = I × R.
- How do I use this calculator?
- Enter any two known values among voltage, current, resistance, and power. The calculator will compute the remaining two using Ohm's Law and the power formula (P = V × I).
- Can I calculate power with this calculator?
- Yes, the calculator includes power calculation. If you provide voltage and current, it will compute power. Alternatively, you can enter resistance and current to find power.
Tips & Common Mistakes
Tips
- Ensure you enter values in consistent units (volts, amps, ohms, watts) to get accurate results.
- Use the calculator to cross-check your manual calculations for circuit problems.
- Remember that Ohm's Law applies to linear resistive circuits; for non-linear components, results may vary.
- If you know power and one other value, you can still find the missing parameters using the power formula.
Common Mistakes to Avoid
- Mixing units, such as using milliamps with ohms without converting to amps.
- Entering only one known value when two are required for calculation.
- Assuming the calculator works for AC circuits with reactive components; it is designed for DC or purely resistive circuits.
Last updated: August 13, 2026