Series & parallel resistor calculator
Enter any number of resistor values to get the series and parallel totals. Below, find the two standard resistors that come closest to a value you do not have.
Make a value from two standard resistors
Formulas
Series: R = R1 + R2 + R3 + … — the same current flows through every resistor and the total is always larger than the largest.
Parallel: 1/R = 1/R1 + 1/R2 + …, or for two resistors R = R1 × R2 ÷ (R1 + R2). The total is always smaller than the smallest. Two equal resistors in parallel give half the value: two 10 kΩ = 5 kΩ.
Examples
| Resistors | Series | Parallel |
|---|---|---|
| 100 Ω, 100 Ω | 200 Ω | 50 Ω |
| 220 Ω, 330 Ω | 550 Ω | 132 Ω |
| 1 kΩ, 1 kΩ, 1 kΩ | 3 kΩ | 333.3 Ω |
| 10 kΩ, 4.7 kΩ | 14.7 kΩ | 3.197 kΩ |
| 1 MΩ, 1 MΩ | 2 MΩ | 500 kΩ |
Combining resistors is also how you spread power: two 1/4 W resistors in series or parallel share the heat, so together they handle 1/2 W. Learn why odd values are missing from the shelf in E-series standard values explained.
FAQ
How do I calculate resistors in parallel?
Add the reciprocals and invert: 1 ÷ (1/R1 + 1/R2 + …). For two resistors, R1 × R2 ÷ (R1 + R2).
How do I make a 5 kΩ resistor?
Two 10 kΩ resistors in parallel give exactly 5 kΩ, or use 4.7 kΩ + 300 Ω in series.