Here's a confusion that trips up upgraders: DDR5 memory often shows higher CAS latency (CL) numbers than DDR4 — a DDR5 kit might be CL30 or CL40, while DDR4 was CL16. At a glance, that makes DDR5 look slower. But it isn't, and the reason is a simple piece of nanosecond math. CAS latency in cycles only tells half the story; what matters is the actual time that delay represents, which depends on the speed. Once you see the math, the "DDR5 is slower" myth disappears.
It's the DDR-generation companion to our latency vs frequency guide and DDR4 vs DDR5.
CAS Latency Is Cycles, Not Time
The key insight: CAS latency (CL) is measured in clock cycles, not in time. A higher CL number isn't automatically slower, because each cycle is shorter at higher speeds. DDR5 runs much faster than DDR4, so even though it takes more cycles to respond, each cycle is briefer — and the actual delay in nanoseconds can be the same or better. Comparing CL numbers across DDR4 and DDR5 directly is meaningless; you have to convert to time.
The Nanosecond Math
The actual latency in nanoseconds is the CL (cycles) divided by the speed (and scaled). Run it on common kits:
- DDR4-3600 CL16 works out to a real latency of roughly ~9 nanoseconds.
- DDR5-6000 CL30 works out to roughly the same ~9–10 nanoseconds — despite its much higher CL number.
- So they're effectively equal in latency — and DDR5 adds far more bandwidth on top. The higher CL number is offset entirely by the higher speed.
This is why a DDR5-6000 CL30 kit isn't "slower" than DDR4-3600 CL16 — it's equal in latency and ahead in bandwidth.
What This Means for You
- Don't fear DDR5's high CL numbers: they're not a sign of slowness — convert to nanoseconds and DDR5 holds its own while adding bandwidth.
- Compare across generations in nanoseconds, not raw CL — that's the only fair comparison.
- For new builds, DDR5 is the standard and the right choice on current platforms; see DDR4 vs DDR5.
- Within DDR5, the same nanosecond logic guides kit choice — see the DDR5 sweet-spot guide.
The Nigeria Tax
This matters practically because some buyers, seeing DDR5's higher CL numbers, wrongly cling to DDR4 thinking it's faster — or overpay for a low-CL DDR5 kit they don't need. The nanosecond math frees you from both errors: DDR5-6000 CL30 is the sensible standard, equal in latency to good DDR4 and far higher in bandwidth, at a sensible price. Compare in nanoseconds, buy the sweet-spot kit, and ignore the misleading raw CL comparison.
Frequently Asked Questions
Is DDR5 slower than DDR4 because of higher CL numbers? No — CAS latency is measured in cycles, not time, and DDR5's much higher speed makes each cycle shorter. Converted to nanoseconds, DDR5-6000 CL30 matches DDR4-3600 CL16 in real latency while adding far more bandwidth.
How do I compare RAM latency across DDR4 and DDR5? Convert CL (cycles) to nanoseconds — divide CL by the speed and scale. Raw CL numbers aren't comparable across generations; only the actual time (nanoseconds) gives a fair comparison.
Should I stick with DDR4 because of latency? No — DDR5-6000 CL30 has effectively the same latency as good DDR4 plus much more bandwidth. For new builds on current platforms, DDR5 is the right standard; don't cling to DDR4 over a misread CL number.
The One Thing to Remember
DDR5's higher CAS latency numbers don't mean it's slower — CL is measured in cycles, and DDR5's higher speed makes each cycle shorter, so DDR5-6000 CL30 matches DDR4-3600 CL16 in real nanosecond latency while adding far more bandwidth. Compare memory across generations in nanoseconds, not raw CL, and DDR5 is clearly the right standard for new builds. Don't be fooled by the bigger number.
Choosing memory for an upgrade? Configure a build online → or talk to our team → and we'll pick the right DDR5 kit — judged on real latency, not misleading CL numbers.