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RAM latency calculator

Convert DDR data rate and CAS cycles into theoretical first-word CAS latency in nanoseconds.

Calculate theoretical CAS latency

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Enter the advertised transfer rate, such as 3200 MT/s—not the half-rate memory clock in MHz.

Enter the CL value, such as 16 for CL16.

RAM latency result

Enter the data rate and CAS cycles, then select Calculate.

How to use the RAM latency calculator

  1. Enter the advertised DDR transfer rate in megatransfers per second (MT/s).
  2. Enter the CAS latency in clock cycles, for example 16 for CL16.
  3. Select Calculate to see theoretical CAS nanoseconds, the underlying memory clock, and one-cycle time.
  4. Edit either input to clear the old result; copy only after a successful calculation.

Why MT/s is not the same as MHz

DDR transfers data on both clock edges. A 3200 MT/s data rate therefore corresponds to a 1600 MHz memory clock.

One clock cycle takes 2000 ÷ data rate nanoseconds. Multiplying that time by CAS cycles gives theoretical CAS latency: CL × 2000 ÷ MT/s.

This isolates one timing component. Controller, topology, queueing, other timings and workload behavior affect complete memory latency.

Worked examples

DDR4-3200 CL16: 16 × 2000 ÷ 3200 = 10 ns; memory clock = 1600 MHz.

DDR5-6000 CL30: 30 × 2000 ÷ 6000 = 10 ns. A larger CL number can still produce the same nanoseconds at a faster data rate.

Limits

  • Inputs must be positive finite numbers; zero, negatives and scientific notation are rejected.
  • MT/s is the effective DDR transfer rate. Do not enter MHz unless the source truly reports MT/s.
  • The result is theoretical CAS latency only, not measured end-to-end latency.
  • This tool does not recommend RAM, predict frame rates, read hardware or apply overclock settings.

Frequently asked questions

Why multiply by 2000?

DDR data rate is twice the memory clock, and a 1 MHz cycle lasts 1000 ns; together that gives 2000 ÷ MT/s.

Is lower always faster?

Lower theoretical CAS nanoseconds helps compare this component, but complete performance depends on the platform and workload.

Can I enter 1600 MHz for DDR4-3200?

No. Enter the advertised 3200 MT/s. The calculator shows the corresponding 1600 MHz clock.