About

When purchasing Random Access Memory (RAM), marketing often emphasizes the Frequency (MHz or MT/s) over the CAS Latency (CL). However, the true speed of memory is a function of both. A higher frequency kit with loose timing can be slower than a lower frequency kit with tight timing. This tool allows for a direct mathematical comparison between two memory configurations.

For example, comparing standard DDR4-3200 CL16 against DDR5-5200 CL40 requires converting both to Absolute Latency in nanoseconds. This tool creates a "Winner" determination based on both access time (responsiveness) and theoretical maximum bandwidth (throughput), helping users make cost-effective upgrading decisions.

Formulas

The calculator uses the standard engineering formula for First Word Latency:

Latency = CAS Latency × 2000Data Rate

Theoretical Bandwidth is calculated for a single channel (Dual Channel doubles this value):

Bandwidth = Data Rate × 81000 GB/s

Reference Data

Memory Standard	Typical Freq (MT/s)	Typical CL	Absolute Latency (ns)	Transfer Rate (GB/s)*
DDR3	1600	9	11.25 ns	12.8 GB/s
DDR3	2133	11	10.31 ns	17.0 GB/s
DDR4	2400	16	13.33 ns	19.2 GB/s
DDR4	3200	16	10.00 ns	25.6 GB/s
DDR4	3600	16	8.88 ns	28.8 GB/s
DDR4	3600	18	10.00 ns	28.8 GB/s
DDR4	4000	19	9.50 ns	32.0 GB/s
DDR5	4800	40	16.67 ns	38.4 GB/s
DDR5	6000	30	10.00 ns	48.0 GB/s

Frequently Asked Questions

Generally, yes. Lower latency means the CPU waits less time for data to be retrieved. However, in modern systems, Bandwidth (higher MHz) is becoming increasingly important for high-core-count CPUs and integrated graphics.

DDR5 architecture is designed for massive bandwidth scalability. While the initial CAS latencies (CL40) result in higher nanosecond delays compared to tight DDR4 (CL14), the massive increase in bandwidth and burst length compensates for this in heavy workloads.

Currently, memory with an absolute latency between 8.5ns and 10ns is considered the sweet spot. Examples include DDR4-3600 CL16 or DDR5-6000 CL30.

No. Rank interleaving provides performance benefits (rank interleaving) that are distinct from raw latency and bandwidth. This tool focuses strictly on the speed capabilities of the modules themselves.