CAS Latency Calculator

Convert CAS Latency (CL) and memory speed in MT/s into true first-word access time in nanoseconds using ns = CL x 2000 / MT/s, then pit two RAM kits against each other to see which one is genuinely faster and by how many nanoseconds and percent, because a lower CL number means nothing until you factor in the clock speed behind it.

🕑Choose a Mode

🎯Head-to-Head Kit Presets

📝Memory Kit Inputs

Memory generation

Labels the kits only; the ns math is the same across generations.

Decimal places on ns

Controls rounding on every latency result.

Kit A memory speed (MT/s)

Rated data rate, for example 6000 for DDR5-6000.

Kit A CAS Latency (CL)

First number in the timing set, e.g. 30 in 30-38-38.

Kit B memory speed (MT/s)

Data rate of the rival kit you are comparing.

Kit B CAS Latency (CL)

CAS Latency of the rival kit, its first timing number.

Overclock target (MT/s)

A speed you plan to tune Kit A to, at the same CL.

Kit A latency 0 ns first-word access time

Kit B latency 0 ns first-word access time

Difference 0 ns gap between the two kits

Kit A memory clock 0 MHz real clock = MT/s / 2

🔢Formula Snapshot

nsCL x 2000 / MT

MHzMT/s / 2

tCK2000 / MT/s

Winlower ns

📊Kit Comparison Grid

Kit	Speed MT/s	CAS CL	Cycle tCK	Latency ns	Relative Rank
DDR4-3200 C14	3200	14	0.625 ns	8.75 ns	Fast
DDR4-3600 C16	3600	16	0.556 ns	8.89 ns	Fast
DDR5-7200 C34	7200	34	0.278 ns	9.44 ns	Quick
DDR5-8000 C38	8000	38	0.250 ns	9.50 ns	Quick
DDR4-3200 C16	3200	16	0.625 ns	10.00 ns	Baseline
DDR5-6000 C30	6000	30	0.333 ns	10.00 ns	Baseline
DDR5-6400 C32	6400	32	0.313 ns	10.00 ns	Baseline
DDR4-3600 C18	3600	18	0.556 ns	10.00 ns	Baseline
DDR5-5600 C36	5600	36	0.357 ns	12.86 ns	Slow
DDR5-4800 C40	4800	40	0.417 ns	16.67 ns	Slow

🧩Same-Speed CL Ladder

Speed MT/s	CL Value	Latency ns	vs Its CL16 or CL30
3600	CL14	7.78 ns	Faster
3600	CL16	8.89 ns	Reference
3600	CL18	10.00 ns	Slower
6000	CL28	9.33 ns	Faster
6000	CL30	10.00 ns	Reference
6000	CL36	12.00 ns	Slower
6400	CL30	9.38 ns	Faster
6400	CL32	10.00 ns	Reference

🔗Speed to Clock and Cycle Time

Data Rate MT/s	Real Clock MHz	Cycle tCK ns	Common Label
3200	1600 MHz	0.625 ns	DDR4-3200
3600	1800 MHz	0.556 ns	DDR4-3600
4800	2400 MHz	0.417 ns	DDR5-4800
5600	2800 MHz	0.357 ns	DDR5-5600
6000	3000 MHz	0.333 ns	DDR5-6000
6400	3200 MHz	0.313 ns	DDR5-6400
8000	4000 MHz	0.250 ns	DDR5-8000

⚙Formula Breakdown

Latency ns = CL x 2000 / MT/sCAS Latency in nanoseconds is the number of clock cycles (CL) multiplied by the length of one cycle. So DDR5-6000 CL30 gives 30 x 2000 / 6000 = 10.00 ns of first-word access time.

Cycle time tCK = 2000 / MT/sEach memory transfer takes 2000 divided by the data rate. At 6000 MT/s one cycle is 2000 / 6000 = 0.333 ns, and CL counts how many of these cycles CAS access needs.

Real clock MHz = MT/s / 2DDR moves data on both clock edges, so the true clock is half the data rate. A 6000 MT/s kit runs at 3000 MHz, which is why cycle time uses 2000 rather than 1000.

Compare by ns, not CL3200 CL16 = 10.00 ns and 3600 CL18 = 10.00 ns are identical despite different CL numbers. The higher CL18 kit is not slower because its faster clock cancels the extra cycle.

Difference and percentThe gap is the two ns values subtracted; the percent is that gap divided by the slower kit. An 8.89 ns kit versus a 10.00 ns kit is 1.11 ns, or about 11 percent, quicker to first word.

Overclock at fixed CLPush a 6000 CL30 kit to 6400 MT/s while holding CL30 and latency drops to 30 x 2000 / 6400 = 9.38 ns, since more speed at the same cycle count means less time.

💡CAS Latency Buying Tips

CL alone is meaningless: A kit advertised as CL16 is not automatically faster than a CL18 kit. DDR4-3200 CL16 and DDR4-3600 CL18 both land at exactly 10.00 ns because the extra cycle on the 3600 kit is shorter. Only compare CL numbers directly when the two kits share the same MT/s; otherwise convert both to nanoseconds first.

Lower ns wins, but by how much: Between DDR5-6000 CL30 at 10.00 ns and DDR5-6400 CL30 at 9.38 ns, the faster kit saves 0.62 ns, roughly 6 percent on first-word access. That gap is real but small, and in most games a 1 to 2 ns edge shifts average FPS by low single digits, so weigh the price premium against the tiny latency payoff.

The spec sheet lies by omission “DDR5-6000 CL30 vs DDR4-3200 CL16, which one is better?” And then it shows those labels, and you’re confused. Low latency looks good on paper, and higher speeds sound great by themselves. What they won’t tell you is how they work together in practice, because manufacturers don’t care about that. That’s where our calculator does all of the math for you. So you don’t need to figure out fractions staring down an online shopping cart. It also converts all of those cycle counts into something real: nanoseconds. Because if CPU is waiting on memory, nanoseconds are the only measurement that matters.

The CAS refers to Column Address Strobe. This means it’s requesting certain columns of data from a currently open row of the memory, and the latency number indicate how long that takes in terms of clock cycles. So yeah sixteen sounds nicer than thirty, but it depends on what your clock speed is. Clock speed dictates how long each tick lasts. If you have a higher frequency then your clock speed runs quicker, so each individual cycle will be shorter. It’s possible a system running with a higher CL number and much higher frequency can still have less total wait time compared to another system with lower CL number and slower frequency. That’s where a lot of folks gets confused when upgrading their systems.

What RAM Speed Is Better?

Once you understand how this works, the formula is straightforward. Multiply the CAS Latency by 2000, then divide that value by the memory speed (in MT/s). Why the 2000? Because DDR only moves data on the rising edge of the clock signal (plus it sends it again on the falling edge), so actual clock rate is half what’s advertised as the data transfer rate. So at 6000 MT/s, a single cycle is about one-third of a nanosecond. It’s double that at 3200 MT/s. Multiply each of these tiny values by the number of cycles needed to complete an access, and there’s your actual delay. In the case of DDR5-6000 CL30, result is 10.00 nanoseconds, a nice round number that eliminates all marketing hooey.

For example, compare DDR4-3200 CL16 and DDR4-3600 CL18. Sixteen is smaller than eighteen, right? So on paper, CL16 wins, but in real life they are equal at 10.00 nanoseconds. Why does the faster 3600 kit has higher latency? Because it’s running so fast that every single tick take less time to do. You can see that immediately if you put speeds into our calculator. The calculator will tell you that you’re wasting your time trying to chase lower CL numbers if speed remains constant. This almost never happens, as new kits typically come with higher speeds and a little bit more relaxed timings.

For competitive gamers who use high refresh rates and low resolutions, every millisecond of frame time matter. Getting that 1% low frame up to 9.38 ns instead of 10.00 ns could make your mouse feel smoother in fast paced shooters. For video editing or office work? You’ll never see a difference. Before CAS latency becomes a limiter, the bottleneck move into CPU architecture and bandwidth. Knowing this informs when you should of spend more on tighter timings and when you can cut corners with standard kits. You can also run overclock simulations with it which is a good way to plan out a build. For example, what happens when you OC a 6000 MT/s kit to 6400 but keep it running at CL30? Latency goes down to 9.38 ns. That’s still using the same amount of cycles, so you have less wait time plus more speed. That is a good thing if your mobo will allow it. The reference table on the page shows how slight increases in speed affect the latency equation.

In conclusion, when it comes to RAM shopping, never let someone sell you on a marketing slogan. Instead, compare similar products. The metric that matters here are nanoseconds, which also applies in both cases. In other words, don’t pay attention to the headline numbers; instead, consider how long it takes for your data to arrive. If you’re building out a gaming rig or a workstation, we do the math for you so you won’t have to guess and buy with confidence. But here’s the thing, faster isn’t always better. It might cost twice as much and only gain you a percent. Now you’ll know exactly what a percentage translates into before you hit the button to buy.