Ohm's Law Calculator
Calculate voltage, current, resistance, and power for linear resistive circuits. Choose a direct calculation mode or enter any two known electrical values to solve the complete relationship with automatic engineering-unit conversion.
Engineering tool
Ohm's Law Calculator
Solve voltage, current, resistance, and power with engineering-unit conversion.
Result console
- Voltage
- 12V
- Current
- 2A
- Resistance
- 6Ω
- Power
- 24W
Electrical relationship summary
Formula: V = I × R
Voltage drives current through resistance; electrical power is P = V × I.
Formula reference
Ohm's Law Formulas
Use volts, amperes, ohms, and watts as base SI units.
Voltage: V = I × RCurrent: I = V / RResistance: R = V / IPower: P = V × IPower: P = I² × RPower: P = V² / RVariable definitions
- V
- voltage in volts
- I
- current in amperes
- R
- resistance in ohms
- P
- electrical power in watts
Worked Example
With I = 2 A and R = 6 Ω:
V = 2 × 6 = 12 V. Power = 12 × 2 = 24 W.
The electrical relationship summary is 12 V, 2 A, 6 Ω, and 24 W.
Engineering Notes
- Ohm's Law is valid for linear resistive circuits.
- Power dissipation should always be verified.
- Temperature changes may affect resistance.
- Measure voltage under load whenever possible.
- Verify resistor power ratings with suitable thermal margin.
Support reference
FAQ
What is Ohm's Law?
Ohm's Law describes the relationship between voltage, current, and resistance in a linear resistive circuit: V = I × R.
How do you calculate voltage?
Multiply current in amperes by resistance in ohms: V = I × R.
How do you calculate resistance?
Divide voltage in volts by current in amperes: R = V / I.
How do you calculate current?
Divide voltage in volts by resistance in ohms: I = V / R.
Can Ohm's Law calculate power?
Yes. Once voltage and current are known, calculate power with P = V × I. Equivalent resistive forms include P = I²R and P = V²/R.
Documentation
Related Engineering Guides
Design notes, guides, and engineering articles linked to this tool.
Engineering Guide
Understanding Electrical Power
Learn electrical power fundamentals, including voltage, current, resistance, watts, energy, Ohm's law, DC and AC power, efficiency, power dissipation, and practical calculations.
18 min · Beginner
Engineering Blog
10 Common Power Design Mistakes (and How to Avoid Them)
Avoid power design mistakes involving watts versus watt-hours, unit prefixes, RMS current, AC power factor, efficiency, derating, thermal design, startup current, voltage drop, batteries, PCB copper, and undersized components.
17 min · Intermediate
Engineering Guide
Engineering Unit Conversions for Electronics
Learn engineering unit conversions for electronics, including SI prefixes, powers of ten, engineering notation, resistance, capacitance, inductance, voltage, current, power, energy, frequency, time, PCB units, and common conversion mistakes.
22 min · Beginner
Related Calculators
Power Calculator
Calculate electrical power, current, or voltage.
AvailableEfficiency Calculator
Calculate conversion efficiency and power loss.
AvailableVoltage Drop Calculator
Estimate wire voltage drop and cable loss.
AvailablePower Supply Current Calculator
Estimate supply current and recommended rating.
AvailableBattery Runtime Calculator
Estimate battery runtime, capacity, or load current.