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Watts to Temperature Rise Formula (Thermal Resistance)
The following formula is used to estimate steadyโstate temperature rise above ambient when a device/material dissipates power through a thermal path with thermal resistance.
Variables:
- ฮT is the temperature rise (K or ยฐC)
- P is the power dissipated as heat (W)
- Rฮธ is the thermal resistance from the heat source to ambient (K/W or ยฐC/W)
To calculate the temperature rise, multiply the power by the thermal resistance. (A temperature difference in kelvins has the same numeric value as a temperature difference in degrees Celsius.)
| Power (W) | Temperature Rise (K) | Temperature Rise (ยฐC) |
|---|---|---|
| 0.1 | 0.4 | 0.4 |
| 0.25 | 1.0 | 1.0 |
| 0.5 | 2.0 | 2.0 |
| 0.75 | 3.0 | 3.0 |
| 1 | 4.0 | 4.0 |
| 1.5 | 6.0 | 6.0 |
| 2 | 8.0 | 8.0 |
| 2.5 | 10.0 | 10.0 |
| 3 | 12.0 | 12.0 |
| 4 | 16.0 | 16.0 |
| 5 | 20.0 | 20.0 |
| 7.5 | 30.0 | 30.0 |
| 10 | 40.0 | 40.0 |
| 12 | 48.0 | 48.0 |
| 15 | 60.0 | 60.0 |
| 18 | 72.0 | 72.0 |
| 20 | 80.0 | 80.0 |
| 22 | 88.0 | 88.0 |
| 24 | 96.0 | 96.0 |
| 25 | 100.0 | 100.0 |
| * Rounded to 1 decimal. Uses ฮT = P ร Rฮธ with Rฮธ = 4.0 K/W. Note: a temperature difference in K equals the same value in ยฐC. | ||
What is Temperature Rise (ฮT)?
Temperature rise (ฮT) is the difference between a heat source temperature and a reference temperature (commonly ambient). In the context of this calculator, ฮT is the steadyโstate temperature increase caused by power dissipation flowing through a thermal resistance (for example, junctionโtoโambient thermal resistance of an electronic component, or conduction through a material layer). This model does not calculate how temperature changes over time based on mass and specific heat.
How to Calculate Temperature Rise?
The following steps outline how to calculate the temperature rise using thermal resistance.
- Determine the power being dissipated as heat (P) in watts (W).
- Determine the thermal resistance (Rฮธ) between the heat source and ambient (K/W or ยฐC/W). This is often provided in datasheets (e.g., RฮธJA) or can be estimated for a simple material layer.
- Use the formula from above: ฮT = P ร Rฮธ.
- If you want absolute temperature, add ambient temperature: Tj = Ta + ฮT.
- Check your result with the calculator above.
Example Problem :
Use the following variables as an example problem to test your knowledge.
Power (P) = 5 W
Thermal Resistance (Rฮธ) = 4.0 ยฐC/W
Ambient Temperature (Ta) = 25 ยฐC
Temperature Rise (ฮT) = P ร Rฮธ = 5 ร 4.0 = 20 ยฐC (same numeric rise as 20 K)
Junction / Component Temperature (Tj) = Ta + ฮT = 25 + 20 = 45 ยฐC
