Dropping Resistor Calculator
Calculate the resistor value required to reduce voltage in a circuit. Features automatic matching to standard E12/E24 resistor series.
Recommended Standard Value (E24)
Closest standard value. Always verify tolerance.
About
In electronics design, a "dropping resistor" is used to reduce the supply voltage to a lower level required by a specific component (the load). This is a fundamental application of Ohm's Law. However, calculating the theoretical resistance is only half the battle; real-world engineering requires selecting a standard resistor value that exists in the market.
This tool calculates the exact resistance and power dissipation required, then intelligently suggests the closest standard values from the E12, E24, E48, and E96 series. This ensures your design is not only theoretically correct but also manufacturable.
Formulas
The calculation is based on Ohm's Law and the Power formula.
Power dissipation in the resistor is calculated to ensure the component does not burn out:
Reference Data
| Series | Tolerance | Values per Decade (10-100) | Common Use Case |
|---|---|---|---|
| E12 | ±10% | 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 | General Purpose, Hobbyist |
| E24 | ±5% | Adds: 11, 13, 16, 20, 24, 30, 36, 43, 51, 62, 75, 91 | Standard Commercial |
| E48 | ±2% | 48 values per decade | Precision Analog |
| E96 | ±1% | 96 values per decade | High Precision / Medical |