RAM Latency Calculator
Enter your RAM’s speed and CAS latency to get its true latency in nanoseconds — the real time the module takes to answer — alongside its bandwidth and memory clock. Or switch to Compare to see whether an upgrade is actually faster.
True latency = CL × 2000 ÷ speed (MT/s)
The real wait for a column access — CAS cycles converted to time.
Great — right in the sweet spot where the best-value kits land.
The box counts transfers per second, and DDR moves two per clock tick — a “6000 MHz” kit really runs a 3000 MHz clock.
CAS numbers only compare within a generation: DDR5 CL30 sounds worse than DDR4 CL16, yet both take 10 ns.
Rated timings are a profile, not a default — most boards boot to slower JEDEC timings. Enable XMP or EXPO in the BIOS to get what you paid for.
The two numbers on a RAM box pull in opposite directions: the speed counts transfers, while the CAS latency counts clock cycles — and a cycle lasts a different amount of time at every speed. That is how DDR5-6000 CL30 and DDR4-3200 CL16, specs that look nothing alike, both answer in exactly 10 nanoseconds — and why judging a kit by its CAS number alone makes new RAM look worse than old. Converting to nanoseconds puts every kit, DDR4 or DDR5, on one honest scale.
How the calculation works
CAS latency (CL) is how many memory-clock cycles pass between the controller asking for a column of data and the module starting to deliver it. Turning cycles into time needs the length of one cycle, and this is where the marketing gets in the way: DDR means double data rate, two transfers per clock tick, so a kit sold as “6000 MHz” really runs a 3000 MHz clock and is properly written 6000 MT/s (megatransfers per second). One cycle therefore lasts 2000 ÷ speed nanoseconds, giving the formula: true latency (ns) = CL × 2000 ÷ speed (MT/s). Bandwidth comes from the same sheet — each transfer moves 64 bits, so peak throughput per channel is speed × 8 bytes: 25.6 GB/s for DDR4-3200, 48 GB/s for DDR5-6000.
Popular kits by true latency
A few common configurations run through the formula. Note how the stock JEDEC speeds memory defaults to before XMP/EXPO — DDR4-2666 CL19, DDR5-4800 CL40 — sit at the bottom despite respectable-looking numbers on the box:
| Kit | True latency | Peak bandwidth |
|---|---|---|
| DDR4-3600 CL16 | 8.9 ns | 28.8 GB/s |
| DDR5-7200 CL34 | 9.4 ns | 57.6 GB/s |
| DDR5-8000 CL38 | 9.5 ns | 64.0 GB/s |
| DDR4-3200 CL16 | 10.0 ns | 25.6 GB/s |
| DDR5-6000 CL30 | 10.0 ns | 48.0 GB/s |
| DDR5-6400 CL32 | 10.0 ns | 51.2 GB/s |
| DDR5-5600 CL36 | 12.9 ns | 44.8 GB/s |
| DDR4-2666 CL19 | 14.3 ns | 21.3 GB/s |
| DDR5-4800 CL40 | 16.7 ns | 38.4 GB/s |
What counts as a good latency?
Under 10 ns is the enthusiast tier, 10–11 ns is where the best-value kits of both generations land, and anything over 13 ns usually means the memory is running its fallback JEDEC profile rather than its rated timings. Two caveats: a nanosecond or two is measurable more than it is feelable, and this is only the CAS portion of a longer trip — the full journey from a CPU cache miss to data arriving takes 50–100 ns once the memory controller and row activation are counted. But CAS-in-nanoseconds is the part you choose when buying, and the fairest single-number comparison between kits.
| True latency | Rating | What it means |
|---|---|---|
| Under 9.5 ns | Excellent | Tuned enthusiast kits — as quick as desktop memory gets |
| 9.5–11 ns | Great | The sweet spot: where well-priced DDR4 and DDR5 kits cluster |
| 11–13 ns | Good | Fine for everyday use; a tuned kit would shave a little off |
| Over 13 ns | Slow | Typical of stock JEDEC timings — check that XMP/EXPO is enabled |