Close this search box.


 How to Check RAM CAS Latency

What is CAS Latency (CL) Ratio?

We often judge a RAM’s performance based on the clock frequency. So, if we have two different RAM sticks that have clock frequencies of 2133Mhz and 2400Mhz respectively, then we think of the 2400MHz RAM to be faster.

However, the clock frequency is only the theoretical limit of a RAM’s performance. There are several other factors like CAS latency, for instance, that affects a RAM’s performance.

CAS Latency is the time delay between a data request and data delivery by the RAM. In short, it is a measure of how quickly the RAM serves up the requested data. CAS Latency is measured in clock cycles.

How to Check RAM CAS Latency?

So, how will you determine your RAM stick’s CAS Latency? It may not be written directly on your RAM. Instead, it might be mentioned within a series of numbers that are printed on your RAM. Each number in the series signifies some timing value and things might start to get confusing at this point.

You can try any of the 4 methods listed below to find the CAS Latency of your RAM without any hassles or potential mistakes.

Method 1: via CPU-Z

By far the easiest method is to install a freeware called CPU-Z. It is a very popular tool that provides all kinds of useful information about your computer’s hardware including the CAS Latency speed of the RAM. You can go through the following steps to know the CAS Latency of your RAM:

Step 1: Get the installer for CPU-Z and install it once the download completes. You can refer to the official CPU-Z site for installation.

Step 2: Once installation is over, launch CPU-Z and navigate to the memory tab.

Step 3: CAS Latency should be mentioned in the Timing box along with other timing information. The number that you read here should be in clock cycles.

Step 4: Next, you can head over to the SPD or Special Presence Detect tab to switch between installed memories on your computer. You can view timing information by selecting a particular memory from the drop-down list.

How to Find the Clock Speed of RAM?

You can also get the clock frequency of the RAM from the memory tab. If you want to know the clock frequencies of all your installed modules, then head over to the SPD tab and go through each and every module. The timing area will have information about clock speed.

Method 2: via Piriform Speccy

Piriform Speccy is another great freeware tool that serves details about your computer’s hardware. To know the CAS Latency of the memory modules on your computer, follow the below-mentioned steps:

Step 1: Download Piriform Speccy from its official site. You can download the free version for this purpose.

Step 2: Launch the application.

Step 3: Go to the RAM section on the UI of the app.

Step 4: You should find the CAS latency of your RAM in this section. It is usually shown in clocks.

Step 5: Piriform Speccy has an SPD or Special Presence Detect functionality using which you can browse through the specs of all your installed memory modules. Simply expand the subsection named SPD.

Step 6: The JEDEC#7 in the Timing table is what indicates the maximum CAS Latency.

Method 3: via Command Prompt

If you don’t want to install third-party apps to know the CAS Latency, then you can also use Windows’ inbuilt tools. You can find out about the part number of your memory module and then use it to search for its specs online or on the manufacturer’s website. Follow the steps given below to check the part number using the command prompt:

Step 1: Start command prompt from the start menu and select run as Administrator.

Step 2: In the command prompt, you can type the following command: wmic memorychip get devicelocator, partnumber and press Enter.

Step 3: You will be provided with a list of all the memory modules that are installed along with their part numbers. Use the required part number and search it on google to reveal the CAS Latency spec.

Method 4: via Physically Examine RAM Modules

The part number of a memory module is usually printed on its body. You can search for this part number to know more about the CAS Latency of this RAM. Alternatively, sometimes, RAM timings may also be printed. It can look somewhat like this – CL15-18-18-36. The numbers that follow the letters ‘CL’ is the CAS Latency measured in clocks.

This method may not be possible in some cases like for Laptops or AIO computers.

Is a Higher or Lower CAS Latency Better?

CAS Latency definitely affects performance. The lower the number, the lower the latency and, hence, the better the performance. The RAM having a lower CAS Latency number will perform better. Of course, this is assuming that all other parameters remain the same including clock frequencies.

The CAS Latency number of your RAM is merely the number of clock cycles it takes for it to serve data after a request is made. This number needs to be multiplied with the duration of one clock cycle to get the delay in units of seconds.

Obviously, the lower the CAS Latency (CL) Ratio, the faster the RAM. But, it also depends on the duration of the clock cycle for the RAM.

Can you Mix CAS Latency RAM?

Sure. You can mix RAMs having different CAS Latencies. However, the motherboard will force the RAM with the lower CL to match the CL of the slower counterpart. Hence, you will only get the performance of the slower memory.

What is a Good CAS Latency for RAM?

CAS Latency provides incomplete data. The clock frequency is what determines the duration of one clock cycle and hence it is required to actually calculate the latency time in seconds (nano seconds to be precise). Therefore, judging a RAM on CAS Frequency alone is incorrect.

Why CAS Latency Matters for RAM?

When comparing two RAM sticks having the same capacity and clock speed, you should consider the CAS Latency to determine which one is superior. The one with the lower CL will outperform the other one due to lower latency.


CAS frequency only holds partial information. Therefore, it should always be considered along with the clock frequency. This is because it entirely depends on the duration of one clock cycle. Also, while mixing two or more RAM modules, you should consider the CL ratio along with other factors. This is because installing a RAM with a higher CL can slow down your system.

One Response

Leave a Reply

Your email address will not be published. Required fields are marked *