CAS Latency (CL)
Also written as: CL timing, column address strobe latency
CAS Latency is how many clock cycles the memory waits between being asked for data and delivering it. A lower CL is only better if you compare it at the same data rate.
When your CPU asks a memory module for a specific column of data, the module doesn't answer instantly — it waits a fixed number of clock cycles first. That count is the CAS Latency, written as CL on the kit's label.
The catch is that a cycle is a unit of time, not a fixed duration. A cycle at DDR5-6000 is shorter than a cycle at DDR5-5600, so the same CL number means less waiting on the faster kit. This is why comparing CL alone across different speeds tells you almost nothing.
To compare fairly, convert both to nanoseconds using the standard formula: latency (ns) = CL ÷ (data rate ÷ 2) × 1000. A CL36 kit at DDR5-6000 and a CL30 kit at DDR5-5000 both work out to 12ns — identical real latency despite very different CL numbers.
Where this decision gets made
RAM / Memory buying guide →
Turn it into a real number
RAM True Latency Calculator →