Ohm’s Law Calculator
Find two unknown electrical quantities from any two measured values. Explore how resistance changes current and power with fixed voltage or current.
Know two values? Find the other two. Calculate voltage, current, resistance and power for one ohmic resistor in a steady DC circuit.
Resistance6 Ω
Power24 W
Show calculation steps
R = V ÷ I = 12 ÷ 2 = 6 Ω. P = V × I = 12 × 2 = 24 W.
Answers are rounded to 7 significant digits. Calculations and unit changes use unrounded values.
What happens when resistance changes?
Choose what stays constant. The same resistance change has opposite effects on power with a fixed voltage and a fixed current.
Preview only; your two measurements stay unchanged.
- Voltage
- 12 V
- Current
- 2 A
- Resistance
- 6 Ω
- Power
- 24 W
Use voltage across the resistor
V = I × R and P = V × I. Voltage is the drop across the component; current is the current through it. Power is electrical dissipation, not its temperature or a safe component rating. Check the component's datasheet and operating conditions when choosing hardware.
Zero values and missing information
A known positive resistance at zero voltage has zero current and power. The same is true for zero current or zero power with known resistance. Two zero measurements without resistance cannot determine resistance. A zero and a nonzero measurement without resistance has no solution in this model of a finite, positive ohmic resistor.
Where this model applies
This tool uses nonnegative magnitudes and constant, positive resistance in steady DC. It does not model a short circuit, open circuit, negative resistance, changing temperature, inductance, capacitance, AC phase angle, or a nonlinear component such as an LED. The exploration assumes an ideal voltage or current source; it does not predict real-source limits or transient behaviour.
For several resistors, use the series and parallel resistor calculator. For an LED circuit, use the LED resistor calculator to account for the LED's forward voltage.
Numbers and units
Use a decimal point, with optional scientific notation such as 1.5e-2. No thousands separators or decimal comma. Up to 24 coefficient digits and an exponent from −24 to 24; nonzero inputs and results in base V, A, Ω and W must lie between 1e-24 and 1e24. Resistance must be greater than zero. Precision of displayed answers does not imply measurement accuracy.
The graph shows V, I and P divided by their original values against the resistance multiplier on a logarithmic horizontal scale. The vertical scale is linear. It describes the equations, not time or temperature. At a zero operating point, voltage, current and power remain zero and their normalized ratios are undefined; absolute preview values remain available.
Formula reference: Fluke: electrical measurements and formulas.
