When shopping for PC memory, many builders notice that while DDR4 typically has low CAS Latency ratings (such as CL14 or CL16), modern DDR5 memory advertises much higher CAS ratings (such as CL30, CL36, or CL40). This causes common confusion: Is DDR5 actually slower in response time than DDR4? The answer lies in True Latency measured in nanoseconds (ns).

1. The True Latency Formula (Nanoseconds vs CAS Latency)

CAS Latency (Column Address Strobe) indicates the number of memory clock cycles it takes for the RAM module to deliver a requested column of data after receiving the memory controller's command. Because clock cycles get significantly shorter as frequency increases, a higher number of cycles at high frequency can equal the exact same real-world time as a lower cycle count at low frequency.

📐
The Universal True Latency Formula:
True Latency (ns) = (CAS Latency ÷ (Data Rate in MT/s ÷ 2)) × 1000
Simplified standard form:
True Latency (ns) = (CL × 2000) ÷ Frequency (MHz)

2. Why CAS Latency Alone is Deceptive

Double Data Rate (DDR) memory transmits data on both the rising and falling edges of the clock signal. Therefore, a RAM module rated at DDR5-6000 MT/s actually operates at a fundamental memory clock frequency of 3000 MHz.

Let's compare two popular enthusiast kits using the formula:

  • DDR4-3200 CL16:
    Latency = (16 × 2000) ÷ 3200 = 32,000 ÷ 3200 = 10.00 ns
  • DDR5-6000 CL30:
    Latency = (30 × 2000) ÷ 6000 = 60,000 ÷ 6000 = 10.00 ns

Even though the DDR5 module's CAS latency number is nearly double (30 vs 16), its real-time response latency is identical: exactly 10.00 nanoseconds. Furthermore, because DDR5 provides nearly double the peak bandwidth (48 GB/s vs 25.6 GB/s per channel) and features dual independent 32-bit subchannels per DIMM, total system throughput is vastly superior.

3. Direct Head-to-Head: DDR4 vs DDR5 Latency Benchmarks

Below is a comprehensive comparison of popular desktop RAM specifications from DDR4 to high-end DDR5:

Memory Kit Clock Frequency CAS Latency (CL) True Latency (ns) Tier Assessment
DDR4-2666 1333 MHz CL19 14.25 ns Budget OEM Baseline
DDR4-3200 1600 MHz CL16 10.00 ns Standard DDR4 Sweet Spot
DDR4-3600 1800 MHz CL16 8.88 ns Enthusiast Low-Latency DDR4
DDR5-4800 2400 MHz CL40 16.66 ns Early Gen 1 DDR5 (Slow)
DDR5-5600 2800 MHz CL36 12.85 ns Mid-Range DDR5
DDR5-6000 3000 MHz CL30 10.00 ns AMD AM5 Optimal Sweet Spot
DDR5-6400 3200 MHz CL32 10.00 ns Intel 14th Gen Sweet Spot
DDR5-7200 3600 MHz CL34 9.44 ns High-End Overclocked DDR5

4. The Impact on 1% Lows & Frame Consistency

In modern CPU-bound gaming scenarios (such as competitive esports titles like CS2, Valorant, Warzone, and Cyberpunk 2077 in crowded city sections), memory latency directly dictates the time the CPU execution pipeline waits for memory fetches (cache misses).

  • Average FPS: Primarily dictated by GPU capability and raw memory bandwidth.
  • 1% and 0.1% Low FPS (Micro-stutter): Heavily influenced by memory latency. A memory kit with lower nanosecond response time minimizes frame hitching, giving a smoother competitive gaming experience.