Enter any two values to solve the rest. Visual circuit sketch updates with your inputs. Use tabs for series/parallel and resistor color codes.
What is Ohm’s Law?
Ohm’s Law states that the voltage (V) across a conductor equals the current (I) through it times its resistance (R): V = I·R. It’s the core relationship used to size resistors, estimate current draw, and determine power dissipation.
How do I calculate power?
Power is the rate of energy use. Using Ohm’s Law, you can compute it as any of P = V·I, P = I²·R, or P = V²/R depending on the known quantities. Always verify a resistor’s wattage rating is above its calculated P.
What’s the difference between series and parallel?
In series, resistances add (Req = R₁+R₂+…), so current is the same everywhere and voltages divide. In parallel, conductances add (1/Req = 1/R₁+1/R₂+…), so voltage is the same across branches and currents divide.
This Ohm’s Law calculator supports voltage/current/resistance/power, series/parallel equivalent resistance, divider visualizations, and a resistor color code helper — all computed locally in your browser.
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This calculator applies standard physics equations using SI units and well‑known constants where applicable. Results derive directly from the input variables and show how changing one parameter affects the others.