Calculator KB-11
Resistor connection calculator
When you don’t have the value you need on hand, combine several resistors to make it.
Result
In brief: Calculate series and parallel resistor combinations: total resistance, current, and power dissipated by each resistor. You can enter values like 10k and 4k7. Example: Total resistance: 761.8 Ω.
Calculation example
| Resistors separated by spaces | 10k 4k7 1k |
|---|---|
| Connection | Parallel |
| Voltage across the combination | 12 V |
| Total resistance | 761.8 Ω |
|---|---|
| In series | 15.7 kΩ |
| In parallel | 761.8 Ω |
| Total current | 15.75 mA |
| Total power | 189 mW |
| Highest power in one resistor | 144 mW |
How it is calculated
Parallel: 1/R = 1/R₁ + 1/R₂ + …
In series, resistances add up and the same current flows through every resistor. In parallel, conductances add up and the voltage is the same across every resistor, so the total resistance is always lower than the smallest resistor’s value.
What to look for
- In a parallel combination, the smallest resistor dissipates the most heat; in series, it’s the largest. Use that resistor to check the power rating.
- Several identical resistors in parallel share the power equally—a common way to build high-power shunts and loads.
Frequently asked questions
How do I calculate the resistance of two resistors in parallel?
R = R1 · R2 / (R1 + R2). The result is always less than the smaller resistor: 10 kΩ and 4.7 kΩ give about 3.2 kΩ.
How can I get a non-standard value using two resistors?
Connecting resistors in series adds their values: 8.2 kΩ and 1.8 kΩ give 10 kΩ. A parallel connection brings the value down: 10 kΩ in parallel with 100 kΩ gives 9.09 kΩ.
Which resistor in a circuit gets hotter?
In a series circuit, the higher-value resistor gets hotter; in a parallel circuit, the lower-value one does. Choose the power rating for each resistor separately, with roughly a twofold margin.
