Every resistor turns electrical energy into heat. Knowing how much power each one dissipates tells you which resistor rating to choose and whether a circuit will overheat.
How to use the Power Dissipation Calculator
- Connection
- Source voltage
- Resistor R1
- Resistor R2
- Resistor R3
- Resistor R4
- Resistor R5
- Resistor R6
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Choose series or parallel, enter the source voltage and up to six resistances (leave unused ones at 0).
Inputs explained
| Field | What to enter |
|---|---|
| Connection | Choose one: Series, Parallel |
| Source voltage | Units: V, mV, kV, µV, MV |
| Resistor R1 | Units: Ω, kΩ, MΩ, mΩ |
| Resistor R2 | Units: Ω, kΩ, MΩ, mΩ |
| Resistor R3 | Units: Ω, kΩ, MΩ, mΩ |
| Resistor R4 | Units: Ω, kΩ, MΩ, mΩ |
| Resistor R5 | Units: Ω, kΩ, MΩ, mΩ |
| Resistor R6 | Units: Ω, kΩ, MΩ, mΩ |
Example values
How the main result changes when Source voltage changes and everything else stays at the example values above:
| Source voltage (V) | Total power (W) |
|---|---|
| 6 | 0.0554 |
| 9 | 0.1246 |
| 12 | 0.2215 |
| 15 | 0.3462 |
| 18 | 0.4985 |
| 24 | 0.8862 |
Formula
Series: I = V/ΣR, P_i = I²·R_i · Parallel: P_i = V²/R_i
Worked example
Inputs — Connection: Series; Source voltage: 12 V; Resistor R1: 100 Ω; Resistor R2: 220 Ω; Resistor R3: 330 Ω; Resistor R4: 0 Ω; Resistor R5: 0 Ω; Resistor R6: 0 Ω.
Results — Equivalent resistance = 650 Ω; Total current = 0.01846 A; Total power = 0.22154 W; Power in R1 = 0.03408 W; Power in R2 = 0.07498 W; Power in R3 = 0.11247 W; Power in R4 = 0 W; Power in R5 = 0 W; Power in R6 = 0 W.
Key terms
- Power rating
- Maximum safe dissipation of a component.
Frequently asked questions
In series, which resistor gets hottest?
The largest one.
In parallel, which resistor gets hottest?
The smallest one.
What rating should a resistor have?
At least twice the dissipated power for reliability.
Does total power depend on connection?
Yes – parallel circuits draw much more from the same voltage.