Enter resistor values to calculate total resistance
Note: The circuit diagram updates automatically as you add or remove resistors.
Note: The circuit diagram updates automatically as you add or remove resistors.
P = V × I (Power = Voltage × Current)
P = V² / R (Power = Voltage² ÷ Resistance)
P = I² × R (Power = Current² × Resistance)
Series Connection:
Rtotal = R1 + R2 + ... + Rn
Parallel Connection:
1/Rtotal = 1/R1 + 1/R2 + ... + 1/Rn
For two resistors in parallel: Rtotal = (R1 × R2) / (R1 + R2)
| Value (Ω) | Value (kΩ) | Value (MΩ) |
|---|---|---|
| 1.0 | 1.0 | 1.0 |
| 1.2 | 1.2 | 1.2 |
| 1.5 | 1.5 | 1.5 |
| 1.8 | 1.8 | 1.8 |
| 2.2 | 2.2 | 2.2 |
| 2.7 | 2.7 | 2.7 |
| 3.3 | 3.3 | 3.3 |
| 3.9 | 3.9 | 3.9 |
| 4.7 | 4.7 | 4.7 |
| 5.6 | 5.6 | 5.6 |
| 6.8 | 6.8 | 6.8 |
| 8.2 | 8.2 | 8.2 |
| Characteristic | Description |
|---|---|
| Resistance | Opposition to current flow (measured in ohms) |
| Tolerance | Allowable deviation from nominal value (e.g., ±1%, ±5%) |
| Power Rating | Maximum power dissipation (e.g., 1/4W, 1/2W, 1W) |
| Temperature Coefficient | Change in resistance with temperature (ppm/°C) |
Given: 5Ω, 10Ω, 20Ω in series
Note: Series connection results in a total resistance greater than any individual resistor.
Given: 5Ω, 10Ω, 20Ω in parallel
Note: Parallel connection results in a total resistance less than the smallest individual resistor.
Resistors combine in two fundamental ways, and knowing the difference is essential for reading any schematic. In series, resistors sit end-to-end so the same current flows through each, and their resistances simply add: Rtotal = R1 + R2 + …. The total is always larger than any single resistor. In parallel, resistors share the same two nodes so they see the same voltage, and the reciprocals add: 1/Rtotal = 1/R1 + 1/R2 + …. The total is always smaller than the smallest resistor, because you are giving current more paths to flow through.
Series is like adding lengths of a narrow pipe — more restriction, higher resistance. Parallel is like opening extra pipes side by side — more total flow, less restriction. For just two resistors in parallel there is a handy shortcut: Rtotal = (R1 × R2) / (R1 + R2). Two equal resistors in parallel give exactly half their value.
Combining resistors lets you hit values that are not sold as standard parts (E12/E24 series), share power dissipation across several resistors so none overheats, and set precise gains and thresholds. Recognising series and parallel groups is also the first step in simplifying and analysing any resistor network before applying Ohm's law or Kirchhoff's laws.
Building non-standard resistance values, current sharing in high-power loads, ladder networks and attenuators, pull-up/pull-down arrangements, and reducing a complex network down to a single equivalent resistance for analysis.
Do parallel resistors always lower the total? Yes — the equivalent is always below the smallest branch, because current has more routes.
How do series/parallel affect power rating? Splitting a load into several resistors (series or parallel) spreads the heat, so each part dissipates less and can use a smaller wattage rating.