Case 1
- Current through the resistor
- 2A
- Resistance
- 10Ω
40.0000W
Open with these valuesPower Dissipation Calculator
40.0000W
Result: 40.0000 WA resistor turns electrical energy into heat at the rate P = I² × R. The current is squared, so doubling it quadruples the heat: 2 A through 10 Ω is 40 W, but 4 A through the same resistor is 160 W. Pick a part whose wattage rating sits well above the answer.
The numbers at a glance
Held fixed: Current through the resistor 2.0000 A.
| Resistance (Ω) | Result (W) |
|---|---|
| 2.500 | 10.0000 |
| 5.000 | 20.0000 |
| 7.500 | 30.0000 |
| 10.000Your value | 40.0000 |
| 12.500 | 50.0000 |
| 15.000 | 60.0000 |
| 17.500 | 70.0000 |
| 20.000 | 80.0000 |
Worked examples
Case 2
- Current through the resistor
- 0.145A
- Resistance
- 220Ω
4.6255W
Open with these valuesCase 3
- Current through the resistor
- 10A
- Resistance
- 5Ω
500.0000W
Open with these valuesHow it's calculated
P = I² × R
- StepEnter the current in amperes — 20 mA is 0.02, not 20.
- StepEnter the resistance in ohms — 4.7 kΩ is 4700.
- ResultRead the heat in watts and choose a part rated above it.
Reference table
| Current, resistance | What it is | Power |
|---|---|---|
| 0.145, 220 | 31.9 V across a 220 Ω resistor | 4.6255 |
| 0.5, 100 | Half an amp through 100 Ω | 25 |
| 1, 1 | The unit case — one amp, one ohm | 1 |
| 2, 10 | The textbook example | 40 |
| 3, 4 | Three amps through 4 Ω | 36 |
| 10, 5 | A heating element, not a signal resistor | 500 |
Questions
How do I calculate power dissipation in a resistor?
Multiply the current squared by the resistance: P = I² × R. Use amperes for the current and ohms for the resistance and the answer comes out in watts. For example, 2 A through a 10 Ω resistor dissipates 40 W.
What is power dissipation?
It is the rate at which a resistor converts electrical energy into heat, measured in watts. Whenever current flows through a resistance the part warms up, and that wasted heat is the dissipated power.
Why does doubling the current quadruple the power?
Because the current is squared in the formula. Power scales with I², so twice the current means four times the heat and three times the current means nine times. A small rise in current can overheat a resistor far more than expected.
What is the voltage drop across the resistor?
That is the current times the resistance, I × R, without the square — 2 A through 10 Ω drops 20 V. The drop grows in proportion to the current while the heat grows with its square.
What units should I use?
Amperes for the current and ohms for the resistance, which gives watts. Convert first: 20 mA is 0.02 A and 4.7 kΩ is 4700 Ω, and entering the milliamp figure directly overstates the heat by a factor of a million.
Sources and last check
Information, not professional advice.