RAM Latency Calculator
Turn a memory kit’s data rate (MT/s) and CAS latency (CL) into real access latency in nanoseconds so you can compare kits fairly.
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Kit A
Kit B
First-word latency = CL × 2000 ÷ data rate. Lower is better. A higher data rate can offset a higher CL, so compare the nanosecond figure rather than the CL number alone.
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What is the RAM Latency Calculator?
This tool converts a memory kit’s advertised data rate and CAS latency into true first-word latency in nanoseconds — the fair way to compare kits with different speeds.
How to use it
- 1Enter the memory data rate in MT/s (e.g. 6000).
- 2Enter the CAS latency (CL) value (e.g. 30).
- 3Read the true latency in nanoseconds.
How it works
The bus clock is half the data rate (DDR transfers twice per cycle). True latency (ns) = CL / (data rate / 2) × 1000 = CL × 2000 / data rate.
DDR5-6000 CL30
Latency = 30 × 2000 / 6000 = 10.0 ns, slightly better than DDR5-6400 CL34 (~10.6 ns).
Limitations & notes
- Only first-word CAS latency is modeled; sub-timings also matter.
- Real workload performance depends on bandwidth, not just latency.
Frequently asked questions
Is DDR5-6000 CL30 better than DDR4-3200 CL16?
Both have the same first-word latency: 30 x 2000 / 6000 = 10 ns, and 16 x 2000 / 3200 = 10 ns. The DDR5 kit moves data almost twice as fast, so it wins in bandwidth-heavy work while matching the DDR4 kit on latency. This is why a higher CL number on newer memory does not automatically mean slower memory.
Is lower CAS latency or higher speed more important?
Compare the nanosecond result first, then bandwidth. If two kits have the same latency, the faster data rate is better. DDR5-7200 CL36 and DDR5-6000 CL30 both come to 10 ns, but the 7200 kit has 20% more bandwidth, although it may need a motherboard and CPU memory controller that can run it stably. Games tend to benefit from low latency; video encoding and large data sets from bandwidth.
Why do some tools show 3000 MHz for DDR5-6000?
DDR memory transfers data twice per clock cycle, so a 6000 MT/s kit has an actual clock of 3000 MHz. Marketing often labels the transfer rate as MHz, which is technically wrong but widespread. This calculator shows both: enter 6000 as the data rate and it reports a 3000 MHz true clock and a cycle time of 0.333 ns.
Do I need to enable XMP or EXPO to get the advertised latency?
Yes. Without a memory profile, most systems boot at a conservative JEDEC default, such as DDR5-4800 CL40, which works out to about 16.7 ns instead of 10 ns for a DDR5-6000 CL30 kit. Enable XMP (Intel) or EXPO (AMD) in the BIOS to run the rated speed and timings, then check stability.
What does this calculator leave out?
It models only CAS latency, the delay before the first word of an already-open row arrives. Real access time also depends on sub-timings such as tRCD and tRP, the memory controller and the CPU's fabric. It also takes whole numbers as you enter them and does not look up kits by part number, so copy the rated speed and CL from the product label.
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