RAM Latency Calculator
Convert CAS latency and RAM speed to real nanosecond latency. Compare two RAM kits side-by-side and discover which is actually faster — because DDR5's higher MHz number doesn't always mean lower latency.
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Kit B
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Kit A
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nanoseconds
Kit B
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nanoseconds
Bandwidth Context
Theoretical single-channel bandwidth. DDR5 DIMMs have two 32-bit channels internally, doubling effective bandwidth.
Common RAM Kits — Reference Table
| Kit | Speed | CL | Latency (ns) | Rating |
|---|
Why MHz Alone Doesn't Tell You RAM Speed
RAM marketing uses MHz (or MT/s) as the headline number, but it only tells half the story. The other half is CAS latency (CL) — the number of clock cycles the RAM takes to respond to a request. At higher clock speeds, each cycle is shorter, so CAS latency in nanoseconds requires the formula: (CL × 2000) ÷ Speed MT/s. This reveals the shocking truth: a DDR5-4800 CL40 kit (16.67ns) is 67% slower in real latency than DDR4-3600 CL16 (8.89ns) — despite having a higher MHz on the box. Always calculate nanoseconds before comparing any two kits. Last updated: March 2026.
DDR5 vs DDR4 Latency — The Real Numbers
The DDR5 generation transition reveals a recurring pattern: early or budget DDR5 kits often have worse real-world latency than well-tuned DDR4. DDR5-4800 CL40 at 16.67ns is worse than DDR4-2666 CL18 at 13.50ns. However, high-end DDR5 kits flip the script: DDR5-6000 CL28 at 9.33ns and DDR5-7200 CL34 at 9.44ns beat even the best DDR4 kits. The sweet spot for DDR5 on AMD AM5 is 6000 MT/s at CL30 or lower, which matches the 2:1 Infinity Fabric ratio. On Intel platforms, 7200–8000 MT/s at low CL delivers the best results.
How CAS Latency Affects Gaming and Workloads
Lower nanosecond latency means the CPU waits less time for data from RAM. In gaming at 1080p with fast CPUs (Ryzen 7 7800X3D), latency differences of 2–3ns can translate to 3–8% FPS differences in CPU-limited scenarios. At 1440p and 4K, the GPU becomes the bottleneck and RAM latency impact shrinks to 1–3%. For content creation — video rendering, 3D animation, large dataset operations — bandwidth (GB/s) often matters more than latency, where DDR5's higher bandwidth wins decisively. For programming and general use, differences under 1ns have no perceptible impact.
How to Choose the Best RAM for Your Budget
Prioritize value-per-nanosecond, not MHz-per-dollar. For DDR4 systems: DDR4-3600 CL16 hits the sweet spot (8.89ns at reasonable cost). Avoid DDR4 over 4000 MHz unless overclocking — the cost premium rarely pays off. For DDR5 on AM5: target 6000 MT/s at CL28–CL30 (around $80–120 for 32GB as of March 2026 after recent price drops). Avoid budget DDR5 kits below DDR5-5600 CL36 — their latency is worse than DDR4. For content creation, prioritize capacity (32GB or 64GB) over speed, since bandwidth scales with capacity in dual and quad-channel configurations.
Frequently Asked Questions
What is CAS latency in RAM?
CAS latency (Column Address Strobe, or CL) is the number of clock cycles the RAM module takes to deliver data after receiving a request. A lower CL number means fewer wait cycles. However, CL alone doesn't determine speed — you must combine it with the clock speed to get the real latency in nanoseconds. Formula: (CL × 2000) ÷ Speed MT/s = nanoseconds. Lower nanoseconds = faster RAM response.
Is DDR5 faster than DDR4 in real latency?
It depends entirely on the specific kit. Cheap or early DDR5 kits (DDR5-4800 CL40 = 16.67ns) are actually slower than most DDR4 kits. High-end DDR5 kits (DDR5-6000 CL28 = 9.33ns, DDR5-7200 CL34 = 9.44ns) are faster than all DDR4 options. The best DDR4 kits (DDR4-4000 CL16 = 8.00ns) rival entry-level DDR5 performance. Always calculate nanoseconds for any kit you're considering.
What is the best CAS latency for gaming?
For DDR4: CL16 at 3200–3600 MT/s (8.89–10.00ns) is excellent. CL18 at 3600 MT/s achieves 10.00ns — identical to DDR4-3200 CL16. For DDR5 on AM5: CL30 at 6000 MT/s (10.00ns) or CL28 at 6000 MT/s (9.33ns) are the recommended gaming sweet spots. On Intel platforms, CL34 at 7200 MT/s (9.44ns) performs very well. Going lower than CL16 for DDR4 or CL28 for DDR5 has diminishing returns unless you're a competitive enthusiast.
Does RAM latency matter for 4K gaming?
At 4K, the GPU becomes the dominant bottleneck — it must render 8.3 million pixels per frame. RAM latency contributes less than 1–3% to overall frame times at this resolution, even between the fastest and slowest RAM kits. RAM latency matters most at 1080p with a fast CPU (like Ryzen 7 7800X3D), where the CPU can process frames faster than the GPU renders them and RAM access time becomes the limiter.
How do I know what CAS latency my RAM is running at?
Open CPU-Z (free download) or HWiNFO64, go to the Memory tab. You'll see the DRAM Frequency (half the MT/s rate for DDR RAM) and CAS Latency. Alternatively, check your BIOS under the memory settings. If you see JEDEC settings, your RAM is running at its default speed; if XMP/EXPO is enabled, it's running at the rated overclock speed on the box.
What does the Infinity Fabric ratio mean for DDR5 on AMD?
AMD's Infinity Fabric (FCLK) ideally runs synchronously with the memory controller (UCLK) for minimum latency. On AM5, the FCLK targets 2000 MHz, which synchronizes with DDR5-4000 MT/s base clock. DDR5-6000 MT/s uses a 2:1 FCLK:UCLK ratio (FCLK 2000 MHz, UCLK 3000 MHz) — AMD's tested and validated target for Ryzen 7000 series. Faster DDR5 beyond 6000 on standard kits can cause async operation, sometimes increasing latency. Always verify with BIOS-reported values.