RAM CAS Latency Calculator

What Is CAS Latency?

CAS Latency (CL) is the number of clock cycles the memory controller must wait after issuing a read command before data starts arriving. It stands for Column Address Strobe — the signal used to select a specific column in a DRAM array, as defined in the JEDEC DDR5 standard (JESD79-5B). A lower CL value means fewer cycles of waiting, but whether that translates to faster real-world latency depends entirely on how fast each clock cycle is.

This is the source of the most common RAM confusion on r/buildapc: a higher MT/s kit does not automatically have lower latency. Because faster RAM has shorter clock cycles, a kit rated CL40 at 6400 MT/s can actually be slower in nanoseconds than a CL30 kit at 6000 MT/s. The only way to know for certain is to calculate the absolute latency using the formula below.

The Formula: MT/s + CL → Nanoseconds

DDR RAM transfers data on both the rising and falling edge of each clock cycle, doubling the effective data rate — hence "Double Data Rate." The actual clock frequency is half the MT/s figure. One clock cycle therefore lasts:

Applied to the classic debate:

The same formula applies to secondary timings (tRCD, tRP, tRAS) — convert any timing from cycles to nanoseconds using cycles × 2000 ÷ MT/s. CL dominates real-world latency for most reads, but tRCD and tRP affect random-access workloads like gaming and desktop responsiveness.

DDR4 vs DDR5 Absolute Latency Reference Table (2026)

Stock DDR5 ships with surprisingly loose timings. The sweet spot for DDR5 is 6000 MT/s with tight CL30 — this is why DDR5-6000 CL30 kits dominate r/buildapc recommendations in 2026 and top Tom's Hardware's best RAM picks. Enable Intel XMP or AMD EXPO in your BIOS to unlock these profiles on supported kits.

★ DDR5-6000 CL30 is the consensus best price-to-latency kit for Intel and AMD platforms in 2026.

Secondary Timings: tRCD, tRP, and tRAS

RAM sticks are internally structured as arrays of rows and columns. Accessing data requires opening a row, then selecting a column. The secondary timings govern how long each of these internal steps takes.

for gaming and desktop use, CL matters most. Content creators doing large sequential reads (video editing, texture baking) benefit from bandwidth, which is determined by MT/s × channel count. for extremely latency-sensitive workloads like real-time audio processing, tight secondary timings compound the improvement from a low CL.

Does RAM Latency Actually Matter for Gaming?

Yes — but only up to a point. Moving from stock DDR5 (≈16 ns) to DDR5-6000 CL30 (10 ns) typically yields 3–8% more FPS in CPU-bound games like CS2, Valorant, and Cities: Skylines, consistent with Tom's Hardware's DDR5 vs DDR4 latency benchmarks. The improvement is most visible at 1080p where the GPU is rarely the bottleneck — use our CPU & GPU Bottleneck Calculator to identify which component limits your frame rate. At 4K, the GPU dominates and RAM latency matters far less.

Within the same latency tier (e.g., comparing two kits both at 10 ns), differences are statistically imperceptible in gaming benchmarks. Spend the savings on a faster GPU instead — use our GPU Price-to-Performance Calculator to find the best value GPU for your remaining budget. RAM latency shows its biggest gains at the transition from Loose/Average to Excellent — particularly the jump from stock DDR5 to a 6000 CL30 or 6400 CL32 kit.

Frequently Asked Questions