What this calculator does
The CAS latency (CL) printed on a memory kit is not a time, it is a count of clock cycles. Two kits with the same CL number can have very different real-world latency if their clock speeds differ, because a cycle takes less time on a faster module. This RAM latency calculator converts CAS latency and clock speed into an actual nanosecond figure, which is what you feel in practice.
The formula is true latency in nanoseconds equals CAS latency divided by the RAM clock speed in MHz, multiplied by 2000. The factor of 2000 accounts for double data rate memory transferring on both the rising and falling edge of the clock, so it takes half a clock cycle, not a full one, to complete a transfer step. Enter the CL number and the rated clock speed from the module label to get the true latency.
The formula
Divide the CAS latency (CL) by the RAM clock speed in megahertz, then multiply by 2,000. The clock cycle time itself is 2,000 divided by the clock speed, and multiplying that by CL gives the true latency directly.
| Term | Meaning |
|---|---|
| CL | CAS latency: the number of clock cycles between a memory read command and the data becoming available. |
| Clock speed | The rated speed printed on the module, in MHz, such as 3200 for DDR4-3200. |
| True latency | The CAS latency converted into an actual time in nanoseconds, allowing fair comparison across different clock speeds. |
The inputs explained
| Field | What to enter |
|---|---|
| CAS latency (CL) | The CAS latency number from the memory kit label or spec sheet, for example 16 or 18. |
| RAM clock speed (MHz) | The rated clock speed in MHz, for example 3200 for DDR4-3200 or 6000 for DDR5-6000. |
When to use it
Comparing two memory kits
A DDR4-3200 CL16 kit and a DDR4-3600 CL18 kit look close on paper, but converting both to nanoseconds shows which one actually responds faster in real time.
Deciding whether a higher CL is worth a higher clock speed
Overclocked kits often carry a higher CL to reach a higher clock speed. Converting to nanoseconds shows whether the extra clock speed actually offsets the looser timing.
Sanity-checking a manufacturer claim
A "low latency" marketing label is a marketing claim, not a number. Converting the actual CL and clock speed on the spec sheet checks it against a real nanosecond figure.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
True latency across common CAS latency values at DDR4-3200
The same clock speed with a range of CAS latency ratings, showing how much CL alone changes real access time.
| CAS latency (CL) | True latency | Time per clock cycle |
|---|---|---|
| CL14 | 8.75 ns | 0.6250 ns |
| CL15 | 9.38 ns | 0.6250 ns |
| CL16 | 10.00 ns | 0.6250 ns |
| CL18 | 11.25 ns | 0.6250 ns |
| CL20 | 12.50 ns | 0.6250 ns |
| CL22 | 13.75 ns | 0.6250 ns |
True latency across common clock speeds at CL16
The same CL16 rating carried across a range of clock speeds, from DDR4 up to faster DDR5 speeds.
| Clock speed | True latency | Time per clock cycle |
|---|---|---|
| 2400 MHz | 13.33 ns | 0.8333 ns |
| 3200 MHz | 10.00 ns | 0.6250 ns |
| 3600 MHz | 8.89 ns | 0.5556 ns |
| 4800 MHz | 6.67 ns | 0.4167 ns |
| 6000 MHz | 5.33 ns | 0.3333 ns |
| 7200 MHz | 4.44 ns | 0.2778 ns |
Questions
Why does a higher CL number sometimes mean lower latency?
Because CL is a cycle count, not a time. A CL18 kit running at a much higher clock speed can have a shorter cycle time overall than a CL14 kit running slower, giving it the lower true latency in nanoseconds.
What counts as a good true latency figure?
Mainstream DDR4 and DDR5 kits typically land somewhere around 8 to 11 nanoseconds. Lower is faster, but the difference between kits a nanosecond or two apart is rarely noticeable outside benchmarks.
Does this formula apply to DDR5 the same way as DDR4?
Yes, the CAS latency to nanosecond relationship is the same across DDR generations, since it depends only on the CL number and the rated clock speed, not the generation itself.
Is a lower CL always better?
Only at the same clock speed. Comparing CL numbers across different clock speeds without converting to nanoseconds first can be misleading, which is exactly what this calculator is for.
For the turning-force side of physics rather than computing hardware, see the torque calculator.