Circuit relationship
What is Ohm's law?
Ohm's law describes the relationship between voltage, electric current, and resistance in an ohmic circuit. Increasing voltage increases current when resistance remains constant.
Increasing resistance reduces current when the applied voltage remains constant. The law is widely used to analyze basic direct-current circuits and electrical components.
Main equation
Ohm's law formula
VoltageV = I × R
- V is voltage in volts.
- I is current in amperes.
- R is resistance in ohms.
Rearranged equations
Solve for current or resistance
Current
I = V ÷ R
Divide voltage by resistance.
Resistance
R = V ÷ I
Divide voltage by current.
Electrical power
Ohm's law power formulas
Electrical power can be combined with Ohm's law to calculate all four circuit quantities.
Voltage and current
P = V × I
Current and resistance
P = I² × R
Voltage and resistance
P = V² ÷ R
Worked example
Find voltage from 2 A and 6 Ω
- Write the equation: V = I × R.
- Substitute the known values: V = 2 × 6.
- Calculate the voltage: V = 12 V.
- Calculate electrical power: P = V × I = 12 × 2 = 24 W.
Standard units
Volts, amperes, ohms, and watts
- Voltage is measured in volts (V).
- Current is measured in amperes (A).
- Resistance is measured in ohms (Ω).
- Electrical power is measured in watts (W).
Convert millivolts, milliamperes, kilo-ohms, or other prefixes to consistent base units before entering values.
Model limitations
Assumptions and limitations
The calculation assumes an ohmic component with effectively constant resistance. Real resistance may change with temperature, current, voltage, material properties, or operating conditions.
Semiconductor devices, lamps, electrolytes, and other non-ohmic components may not follow a constant linear voltage-current relationship. Complex alternating-current circuits may also require impedance and phase calculations.
Questions and answers
Ohm's law calculator FAQ
What formula does the Ohm's law calculator use?
The primary formula is V = I × R, where V is voltage, I is current, and R is resistance. It also uses P = V × I and equivalent electrical power formulas.
Can this calculator find electrical power?
Yes. It can calculate power from voltage and current, current and resistance, or voltage and resistance.
What units should I use for Ohm's law?
Use volts for voltage, amperes for current, ohms for resistance, and watts for power.
Can voltage, current, or resistance be zero?
This calculator requires positive, non-zero inputs because several rearranged formulas divide by these quantities.
Does Ohm's law apply to every electrical component?
No. The simple relationship V = I × R is most appropriate for ohmic components whose resistance remains effectively constant under the stated conditions.