Enter the data rate (MT/s—often marketed as “MHz”) or the base memory clock (MHz) and CAS latency of your RAM into the calculator to determine the RAM value (true latency) in nanoseconds. This value helps you compare the real first-word latency of different RAM modules.

RAM Value Calculator

Find true latency in nanoseconds, or pick the better-value kit.

True Latency
Compare Kits

RAM Value Formula

The following formula is used to calculate the RAM value (true CAS latency) in nanoseconds.

RAM Value (ns) = (CL / Memory Clock (MHz)) × 1000 = (CL × 2000) / Data Rate (MT/s)

Variables:

  • CL (CAS latency) is the number of memory clock cycles between a READ command and when the first data becomes available (cycles).
  • Memory Clock is the actual clock rate in MHz (for DDR memory, Memory Clock = Data Rate ÷ 2).
  • Data Rate is the effective DDR speed in MT/s (often marketed and mislabeled as “MHz,” e.g., “DDR4-3200”).

To calculate the RAM value, use the real memory clock in MHz, or use the DDR data rate in MT/s with the equivalent form of the formula above.

What is RAM Value?

RAM value, often referred to as true latency, is a measure of the CAS (first-word) access delay of RAM in nanoseconds. It helps you compare RAM beyond just frequency (data rate) or CAS latency alone. A lower RAM value means lower CAS delay, though overall performance also depends on bandwidth, other timings, and the workload.

How to Calculate RAM Value?

The following steps outline how to calculate the RAM Value.

  1. First, determine the RAM data rate in MT/s (for DDR memory, this is the advertised speed such as 3200 MT/s) or determine the base memory clock in MHz (half the MT/s value).
  2. Next, determine the CAS latency of the RAM (CL, in cycles).
  3. Use the formula: RAM Value (ns) = (CL / Memory Clock (MHz)) × 1000, or equivalently RAM Value (ns) = (CL × 2000) / Data Rate (MT/s).
  4. Finally, calculate the RAM Value (in nanoseconds).
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Data Rate (MT/s) = 3200 (DDR4-3200), so Memory Clock = 1600 MHz

CAS Latency (CL, cycles) = 16, so RAM Value = (16 × 2000) / 3200 = 10 ns