What the RAM latency calculator does
Memory is advertised with two numbers — a speed in MT/s (often labelled MHz) and a CAS latency in clock cycles — and neither alone tells you which kit is faster. This calculator converts them into the true latency in nanoseconds, so DDR4-3200 CL16 and DDR5-6000 CL30 can be compared directly. Runs in your browser.
The formula
True latency (ns) = CAS latency × 2000 ÷ transfer rate (MT/s)
The factor of 2000: DDR transfers twice per clock, so the clock is half the MT/s figure,
and one cycle in ns = 1000 ÷ clock MHz = 2000 ÷ MT/s.
DDR4-3200 CL16: 16 × 2000 ÷ 3200 = 10.0 ns
DDR4-3600 CL18: 18 × 2000 ÷ 3600 = 10.0 ns (same latency, more bandwidth)
DDR5-6000 CL30: 30 × 2000 ÷ 6000 = 10.0 ns
DDR5-5600 CL40: 40 × 2000 ÷ 5600 = 14.3 ns (a typical JEDEC-spec kit — noticeably slower)The CL number has stayed at roughly 10 ns of real latency across generations while bandwidth has multiplied. A higher CL on a faster kit is not worse; it is the same time measured in shorter cycles.
Common kits compared
| Kit | Latency | Bandwidth (dual channel) | Notes |
|---|---|---|---|
| DDR4-2666 CL19 | 14.3 ns | 42.7 GB/s | Basic JEDEC |
| DDR4-3200 CL16 | 10.0 ns | 51.2 GB/s | The DDR4 sweet spot |
| DDR4-3600 CL16 | 8.9 ns | 57.6 GB/s | Good Ryzen 5000 pairing |
| DDR5-4800 CL40 | 16.7 ns | 76.8 GB/s | Basic JEDEC DDR5 |
| DDR5-5600 CL36 | 12.9 ns | 89.6 GB/s | |
| DDR5-6000 CL30 | 10.0 ns | 96 GB/s | The Ryzen 7000/9000 sweet spot |
| DDR5-6400 CL32 | 10.0 ns | 102.4 GB/s | |
| DDR5-7200 CL34 | 9.4 ns | 115.2 GB/s | Intel-oriented; may need tuning |
Latency vs bandwidth
- Latency (this calculator) is how long a single request waits. It matters most for games, compilers, databases and anything with unpredictable memory access.
- Bandwidth is how much data streams per second: MT/s × 8 bytes × channels. It matters for video encoding, large-array science, integrated graphics and memory-heavy rendering.
- A kit can win on one and lose on the other. DDR4-3600 CL16 has lower latency than DDR5-5600 CL36 but far less bandwidth; which is “faster” depends on the workload.
- CAS latency is only the first of several timings (tRCD, tRP, tRAS); kits with the same CL can differ in the others. CL is the headline because it dominates random access.
Platform notes
- AMD Ryzen: the memory controller clock is tied to the memory speed; DDR5-6000 (Zen 4/5) and DDR4-3600 (Zen 3) are the fastest speeds at which it runs 1:1. Faster kits force a 2:1 divider that adds latency and usually loses performance.
- Intel: scales with speed more freely; 7,000+ MT/s kits benefit some workloads, but latency in ns is still the number to compare.
- XMP / EXPO: the advertised speed and CL only apply after enabling the profile in BIOS; otherwise the kit runs at a slower JEDEC default.
- Four sticks often cannot reach the speed two can; check the motherboard's qualified list.
Frequently asked questions
Is lower CL always better?
Only at the same speed. Compare the latency in nanoseconds — that is what this calculator gives you. CL16 at 3200 equals CL18 at 3600.
How much does RAM latency affect gaming?
Typically a few percent between a good and a mediocre kit at the same capacity, more on CPU-bound titles and integrated graphics. Capacity (16 vs 32 GB) and dual-channel matter more than fine timings.
Is MHz the same as MT/s?
Marketing uses MHz, but DDR4-3200 runs a 1600 MHz clock with 3200 million transfers per second. Enter the advertised number; the calculator's formula already accounts for this.
What does the rest of the timing string (16-18-18-38) mean?
CL-tRCD-tRP-tRAS: column access, row-to-column delay, row precharge, and row active time, all in cycles. Convert each with the same 2000 ÷ MT/s factor.
Does DDR5 have higher latency than DDR4?
Entry-level DDR5 kits do; tuned DDR5 (6000 CL30) matches good DDR4 at about 10 ns while offering roughly double the bandwidth.
Are my values stored?
No. The calculation runs in your browser.