In the most simplest terms, Thermal Design Power (TDP) is the measure of the amount of HEAT the processor generates.
This rating is used to choose the Cooling System of your computer (NOT THE POWER SUPPLY)
Below we will read a bit in depth into various elements of TDP and try to answer What is TDP in CPU.
As mentioned earlier, thermal design power is a specification found on all processors. It basically tells us how much heat a processor is expected to produce during relatively heavy use.
Note that heavy use is not the same as peak heat production. The peak heat that a processor producers can go way beyond the rated TDP heat.
This can happen in instances when you are affected by a power virus or if you overclock your CPU.
What Factors affect the Heat Generation of the Processor?
There are plenty of factors that can affect how much heat a processor generates.
1. Clock Speed
The higher the clock speed of the processor, the more heat it will produce.
This point is very important to note if you are going to overclock your CPU.
The rated TDP specifies the heat generated by the NON-overclocked/Vanilla processor. It DOES NOT specify the heat generated once you overclock it!
Once you clock your processor, you will need to compensate/dissipate the heat it with a much better cooling system like Water Cooling, or else overclocking can reduce the lifespan of the CPU.
2. Use-Case / Platform
Basically, depending on which platform the processor will be installed on, the TDP changes.
Desktop processor have the highest TDP. Laptop and Tablet processor have lower TDPs.
Here is an example of how Use-Case would affect the choice of the Core i7 processor from the 8th generation, and hence the TDP.
As you can see, the smaller the chassis or the less demanding the use case, the lower would be the TDP.
The latest processors from both AMD and Intel use the mechanism of Configurable TDP. With this, the processor’s TDP can be adjusted depending upon the platform it will be used on.
For Instance, the Core i7-8665U has a nominal TDP of 15W but a configurable TDP of Maximum 25W and Minimum 10W. So if this processor was featured in mainstream laptop, the TDP can be upped to the maximum level.
However, if it was featured in a compact tablet, then the TDP would be brought down to 10W.
Of course, this affects the overall clock speed. Lower TDP means you are lowering the clock speed of the processor and hence its performance. So it's important to keep in mind depending on how much processor speed you need.
3. Physical Size
The larger the processor physically, the more heat it would naturally produce.
For instance, Core i7-8850H has a size of 42mm x 28mm and a TDP of 45W.
On the other hand, Intel Celeron N4000 has of 25mm x 24mm and a TDP of mere 6W. Yet, they are both processors for laptops.
Is TDP the Same as Rated Power?
TDP is NOT the same as rated power!
There is often a misconception that the TDP of a processor is the rated power of the processor too.
This misconception probably arises from the fact that Heat Transfer and Power Consumption are both measured in Watts.
While they are not the same, they both ARE related! A high performance i7 processor with multiple cores is going to consume more Power and thus have a higher TDP than, say, a low performance Intel Atom processor which draws a fraction of the power from the wall.
So the key point to remember here is that TDP and Power Consumption are two different aspects of a processor but they are related.
Take the latest extreme performance Core i9-9900K processor.
According to the specifications, this processor has a TDP of 95W:
Intel Core i9-9900K TDP is 95W [Courtesy: Intel.com]
Yet in the tests conducted by Tom’s Hardware, this processor reached as high as 249.7 watts power draw as shown below.
This proves the fact that TDP is not the same as power rating.
Intel Core i9-9900K Power Benchmark [Courtesy: TomsHardware.com]
They had the processor water cooled to compensate for the corresponding heat generated by a processor consuming 249.7 Watts.
This obviously raises some questions
If you were to design the cooling of your system keeping the rated TDP in mind, what would happen if the processor somehow exceeds that cooling capacity?
This CAN happen in certain situation for instance if you get attacked by a Power Virus. It can also happen if you plan to overclock but you have no idea what you are getting into.
The good news is that there is a fail safe feature in every processor: Maximum Junction Temperature. we discuss this below.
The key take away in this section is that if anyone asks what is TDP in CPU, it is imperative to know that it is NOT the rated power, instead, it is the amount of heat generated.
Maximum Junction Temperature (TJ max)
All processors have a fail safe mechanism in case the Junction Temperature (operating temperature) reaches a maximum point.
Most CPUs have a TJ Max of 100°C (212°F). You can find this on the specs-sheet of all processors.
When the CPU cores approach the TJ Max value (at around 90°C or so), they will either start to throttle (reduce the clock speed) or the system will shut down the computer to protect itself from thermal damage if it exceeds the TJ max.
Therefore, coming back to the earlier concern: if you have poor cooling design or if you were attacked by a power virus, there IS a fail safe mechanism in all processors.
However, there most certainly are viruses that can bypass the fail safe programming and kill your processor i.e MPrime, BPUburn-in, FurMark etc.
One way to check your CPU’s Operating Temperature and TJmax is to install a very handy little software called Real Temp. This is the most famous small utility for temperature monitoring. You can also look into undervolting the CPU to prevent it from reaching the TJ max value.
People Also Ask (FAQs)
Why is the TDP an Ambiguous/Misleading Number?
Unfortunately, the specified TDP value is based on the manufacturer’s discretion. There is no hard and fast rule as to how the TDP is defined.
Some brands use the most strenuous scenarios in mind to specify the TDP for their processors, while others define their TDP based on TYPICAL/AVERAGE use.
How CPU TDP Rating Helps with Cooling Design?
All active cooling system including Airflow Cooler and Water Cooled Systems also have a TDP rating that defines the heat they are designed to dissipate.
Check out the product table below by CoolerMaster. It shows how much TDP each model is designed to dissipate.
CoolerMaster Model and TDP Specification [Courtesy: CoolerMaster.com]
You should note however that if you planning on overclocking your CPU, you must get a Cooler that has a higher TDP rating than your CPU.
What is Peak Power Consumption of a CPU?
So if the TDP rating is not the same as Power Draw rating, then how do you find out the peak power that your processor CAN consume?
Well, unfortunately, the processor spec sheets do not mention the peak power consumption.
To figure this out yourself, you will need to provide enough cooling and then overclock your processor to the limit and then measure its peak power consumption at that point.
Andrew White is the founder of TechGearoid, a leading technology review & information website that is designed to help consumers make better decisions when it comes to their IT purchases. As a specialist tech writer (nerd) with over 10 years of experience, he enjoys writing about everything there is to do with modern technology & the newest market innovations. When he isn’t providing value for his readers, he’s usually drinking coffee or at the beach. Andrew lives in Sydney, Australia with his wife and family.