Tool 518 · Resistive-circuit intelligence
Ohm’s Law Calculator
Solve voltage, current, resistance and power, check resistor loading, analyze a loaded voltage divider, or design an LED series resistor with preferred-value recommendations — entirely in-browser.
Smart 4-variable solverAny two of V, I, R, P — extra inputs are consistency-checked.
Rating awarenessPower utilization, derating target and common wattage recommendation.
Loaded dividerIncludes Thevenin output resistance and load-induced sag.
LED resistor designE12/E24 choices and actual current from the selected preferred value.
Enter any two electrical quantities
The tool solves the other values. If you enter three or four, it checks whether they agree within the selected tolerance instead of silently ignoring conflicts.
Ohm’s law + resistive power
This mode models a positive, purely resistive DC load. Zero-value short/open-circuit edge cases are intentionally not inferred from ambiguous input pairs.
Resistor dissipation and rating headroom
This is an electrical dissipation check, not a thermal guarantee. Real component derating depends on resistor technology, ambient temperature, PCB layout, enclosure and manufacturer data.
Voltage divider with optional load
Leave RL blank for an unloaded divider. The loaded calculation uses R2 ∥ RL and also reports the Thevenin voltage and output resistance seen by the load.
LED series resistor
Forward voltage varies with device, current and temperature. The recommended preferred resistor is chosen at or above the ideal resistance so calculated current does not exceed the target under the entered nominal Vf.