RAM Latency Calculator — CAS Latency to Nanoseconds
A CAS latency number means nothing without the clock speed behind it. Enter the CL and the DDR transfer rate to get the true memory access delay in nanoseconds — the correct unit for comparing different RAM kits.
DDR generation
MT/s
Actual memory access delay in nanoseconds — lower is faster
Actual clock = transfer rate ÷ 2 (DDR uses both clock edges)
Cycle time = 1 000 ÷ actual clock (MHz)
True latency = CAS cycles × cycle time
- 1
Actual clock speed
3,200 ÷ 2 = 1,600DDR transfers on both clock edges, so the real internal clock is half the advertised transfer rate. - 2
Clock cycle duration
1,000 ÷ 1,600 = 0.625 - 3
True CAS latency
16 × 0.625 = 10
How does this calculator work?
True RAM latency (ns) = CAS × 2 000 ÷ transfer rate (MT/s). DDR memory runs its real clock at half the advertised MT/s speed, so a DDR4-3200 cycle is 0.625 ns. CL16 DDR4-3200 = 10 ns; CL36 DDR5-6000 = 12 ns. Compare kits in ns, not CL cycles.
Formula
How this is calculated
DDR (Double Data Rate) memory transfers data on both the rising and falling edges of its clock signal, so the actual internal clock frequency in MHz is exactly half the advertised transfer rate in MT/s. DDR4-3200 runs its real clock at 1 600 MHz, not 3 200 MHz. One clock cycle therefore takes 1 000 ÷ 1 600 = 0.625 nanoseconds.
CAS Latency (CL) is the number of clock cycles the memory controller waits between issuing a column read command and receiving the first valid data bit. Multiply the cycle count by the cycle duration to get the true latency: CL × (1 000 ÷ (speed ÷ 2)). For CL16 DDR4-3200 that is 16 × 0.625 = 10.0 ns. For CL36 DDR5-6000 it is 36 × (1 000 ÷ 3 000) = 12.0 ns — despite the far higher raw bandwidth, this DDR5 kit has worse CAS latency than the DDR4 example.
This matters for latency-sensitive workloads such as gaming (1% low frame times), real-time audio and memory-bandwidth-bound simulations. Always compare kits in nanoseconds, not cycles. DDR5 kits typically carry larger CL numbers; check whether the true ns latency is actually competitive with a DDR4 alternative before paying a premium.
Frequently asked questions
DDR stands for Double Data Rate — data is transferred on both the rising and falling edges of each clock pulse, doubling throughput over the physical clock. DDR4-3200 has a real clock of 1 600 MHz; DDR5-6000 runs at 3 000 MHz. The "MT/s" (megatransfers per second) figure already counts both edges.
Lower CL is better only when comparing kits at the same speed. Across different speeds you must compare true nanoseconds. A CL16 DDR4-3200 kit (10.0 ns) beats a CL18 DDR4-3200 kit (11.25 ns), but both can lose to a CL30 DDR5-6000 kit if that kit's true latency is lower on your platform.
Yes — DDR5 still uses double-data-rate transfers, so the same formula applies: actual clock = speed ÷ 2, cycle time = 1 000 ÷ actual clock, true latency = CL × cycle time. DDR5 typically shows CL 36–50+ but at much higher speeds, keeping true latency competitive with late DDR4.
Also known as
TG we-Calculate Editorial Team. (2026). RAM Latency Calculator — CAS Latency to Nanoseconds [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/ram-latency-calculator
TG we-Calculate Editorial Team. "RAM Latency Calculator — CAS Latency to Nanoseconds." TG we-Calculate. 2026. https://we-calculate.com/calculator/ram-latency-calculator.
TG we-Calculate Editorial Team, "RAM Latency Calculator — CAS Latency to Nanoseconds," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/ram-latency-calculator
@misc{wecalculate_ram_latency_calculator, title = {RAM Latency Calculator — CAS Latency to Nanoseconds}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/ram-latency-calculator}}, year = {2026}, note = {TG we-Calculate} }
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