RAM Latency Calculator
Enter your memory data rate and CAS latency to see the true access delay in nanoseconds, which is far more useful for comparing kits than the raw CL number alone. You can also add the secondary timings (tRCD, tRP, tRAS) to convert each one to nanoseconds and see the total row cycle time. The bandwidth output shows peak throughput per channel. Results update as you type.
Why CAS latency in nanoseconds matters more than the CL number
Memory manufacturers advertise RAM using a cycle count such as CL16 or CL30. That number means nothing on its own because a clock cycle gets shorter as the data rate increases. A DDR4-3200 CL16 kit and a DDR5-6000 CL30 kit both have a true latency of exactly 10 ns, even though the cycle counts are very different. The only meaningful comparison is the nanosecond figure, which this calculator gives you. Faster RAM that carries a higher CL can easily beat slower RAM with a lower CL once you look at nanoseconds.
How to read a full timing string
Most kits are sold with a four-number timing string such as 16-18-18-38. The numbers refer to tCL (CAS latency), tRCD (RAS-to-CAS delay), tRP (row precharge), and tRAS (active-to-precharge). tCL is the latency that matters most for random reads. tRCD is the delay before the column can be addressed after a row is opened. tRP is the time to close a row before opening another. tRAS sets the minimum time a row stays active. Enable the "Include secondary timings" toggle to convert all four values to nanoseconds. tRC (row cycle time) = tRP + tRAS and determines how quickly the memory controller can cycle through rows.
DDR4 vs DDR5 latency in practice
Early DDR5 kits shipped with high CL40 timings that produced latencies above 16 ns, noticeably worse than a well-tuned DDR4-3600 CL16 kit at 8.89 ns. By the time DDR5-6000 CL30 kits became mainstream, the two generations reached the same ~10 ns level. DDR5-7200 CL34 and faster kits now beat typical DDR4 on true latency while also offering much higher bandwidth (roughly 51 GB/s at DDR5-6400 versus 25.6 GB/s at DDR4-3200). For most users upgrading platforms, the bandwidth gain matters more than the marginal latency difference.
Latency targets by workload
Competitive esports games (CS2, Valorant, Apex) are the most latency-sensitive consumer workload because game engines poll input and physics many hundreds of times per second. A true latency below 9 ns is the enthusiast target for these titles. General 1080p and 1440p gaming gets the most from latency below 11 ns. Productivity workloads such as video editing and compiling are dominated by bandwidth rather than latency, so a dual-channel setup at a high data rate matters more than shaving nanoseconds. Server and workstation ECC kits typically run at higher latencies, but error correction and capacity take priority over raw access speed in those environments.
Common RAM configurations and true latency
| Generation | Data rate (MT/s) | CAS latency | True latency (ns) | Use case |
|---|---|---|---|---|
| DDR4 | 2133 | CL15 | 14.08 | Entry level |
| DDR4 | 3200 | CL14 | 8.75 | Gaming - excellent |
| DDR4 | 3200 | CL16 | 10.00 | Gaming - mainstream |
| DDR4 | 3600 | CL16 | 8.89 | Gaming - excellent |
| DDR4 | 3600 | CL18 | 10.00 | Gaming - good value |
| DDR4 | 4000 | CL18 | 9.00 | Enthusiast |
| DDR5 | 4800 | CL40 | 16.67 | DDR5 entry (avoid) |
| DDR5 | 5600 | CL36 | 12.86 | DDR5 mainstream |
| DDR5 | 6000 | CL30 | 10.00 | DDR5 sweet spot |
| DDR5 | 6400 | CL32 | 10.00 | DDR5 performance |
| DDR5 | 7200 | CL34 | 9.44 | DDR5 high-end |
| DDR5 | 8000 | CL38 | 9.50 | DDR5 enthusiast |
Reference values for popular kits across DDR4 and DDR5 generations. True latency (ns) = CL x 2000 / data rate.
Frequently asked questions
What is CAS latency and why does it matter?
CAS (Column Address Strobe) latency is the delay in clock cycles between the memory controller issuing a READ command and the memory module returning the first bit of data. It is measured in clock cycles, so its real-world meaning depends on the clock speed. A shorter true latency (nanoseconds) means the CPU waits less time for data from RAM, which benefits any workload that makes many small, random reads.
What is the formula for true RAM latency?
True latency (ns) = CAS latency (cycles) x 2000 / data rate (MT/s). The 2000 factor comes from the fact that DDR memory transfers data on both the rising and falling edges of the clock, so the actual clock frequency is half the data rate, and 1 / (data_rate / 2) expressed in nanoseconds simplifies to 2000 / data_rate.
Is DDR5 always slower than DDR4 on latency?
No. Early DDR5 kits (DDR5-4800 CL40) had much higher true latency than contemporary DDR4, but newer DDR5 kits achieve comparable or better latency. DDR5-6000 CL30 and DDR5-7200 CL34 both deliver around 9-10 ns, matching or beating a typical DDR4-3200 CL16 kit at 10 ns. The advantage of DDR5 is bandwidth: it is roughly double that of DDR4 at similar data rates, which benefits workloads that move large blocks of data.
Should I prioritize CAS latency or data rate when buying RAM?
For gaming, look at the nanosecond figure rather than either number alone. A DDR4-3600 CL16 kit (8.89 ns) is better than DDR4-3200 CL16 (10 ns) despite having a higher CL. For creative work, video rendering, or AI, bandwidth matters more: buy the fastest data rate you can afford with reasonably tight timings. Always compute the nanosecond latency before comparing prices.
What do tRCD, tRP, and tRAS mean?
tRCD (RAS-to-CAS Delay) is the number of cycles between activating a row and being able to issue the column read command. tRP (Row Precharge) is the cycles required to close an active row before the next one can open. tRAS (Active-to-Precharge) is the minimum time a row must remain active. Together with tCL, these four timings form the primary timing string printed on kit labels and shown in the BIOS. Lower values mean faster operation, but stability depends on the specific memory chips and controller.
What is peak bandwidth and how is it calculated?
Peak bandwidth (GB/s) = data rate (MT/s) x 8 bytes / 1000. The 8 bytes comes from the 64-bit memory bus width (8 bytes per transfer). For example, DDR5-6400 delivers 6400 x 8 / 1000 = 51.2 GB/s per channel. A dual-channel setup doubles this to 102.4 GB/s. Note that real-world bandwidth is typically 80-90% of this theoretical peak due to command overhead and refresh cycles.