RAM Latency Calculator

About RAM Latency Calculator

RAM speed is quoted in MHz and CAS latency (CL) numbers, but neither tells the full story on its own. This calculator converts those specs into true latency in nanoseconds - the actual time the memory takes to respond to a request. It works for DDR4 and DDR5, with a comparison mode to evaluate two kits side by side.

The True Latency Formula

DDR (Double Data Rate) memory transfers data twice per clock cycle, so the actual clock speed is half the advertised transfer rate. True latency is calculated from the CAS latency and the real clock speed:

True Latency (ns) = (CAS Latency / Real Clock Speed) x 1000

Or equivalently: True Latency (ns) = (CAS Latency / (Transfer Rate / 2)) x 1000

RAM Kit	Transfer Rate	Real Clock	CAS Latency	True Latency
DDR4-3200 CL16	3200 MT/s	1600 MHz	16	10.00 ns
DDR4-3600 CL16	3600 MT/s	1800 MHz	16	8.89 ns
DDR4-3600 CL18	3600 MT/s	1800 MHz	18	10.00 ns
DDR5-5600 CL28	5600 MT/s	2800 MHz	28	10.00 ns
DDR5-6000 CL30	6000 MT/s	3000 MHz	30	10.00 ns
DDR5-6000 CL36	6000 MT/s	3000 MHz	36	12.00 ns
DDR5-6400 CL32	6400 MT/s	3200 MHz	32	10.00 ns
DDR5-7200 CL34	7200 MT/s	3600 MHz	34	9.44 ns
DDR5-8000 CL38	8000 MT/s	4000 MHz	38	9.50 ns

Lower nanoseconds = faster response. Notice that DDR4-3600 CL16 and DDR5-7200 CL34 are surprisingly close in true latency, despite the DDR5 kit having a CL number more than twice as high.

DDR4 vs DDR5: Latency and Bandwidth

DDR5 has higher CAS latency numbers than DDR4, which looks worse on paper. But DDR5 also runs at much higher transfer rates, so the true latency in nanoseconds is similar or sometimes better. Where DDR5 clearly wins is bandwidth.

Spec	DDR4-3600 CL16	DDR5-6000 CL30	DDR5-7200 CL34
True latency	8.89 ns	10.00 ns	9.44 ns
Bandwidth (dual channel)	28.8 GB/s	48.0 GB/s	57.6 GB/s
Typical gaming impact	Very responsive at 1080p	Good all-round	Best for bandwidth-hungry workloads

For gaming at 1080p where the CPU is the bottleneck, latency matters more than bandwidth. For 4K gaming where the GPU is the bottleneck, RAM latency has minimal impact. For productivity workloads like video editing, 3D rendering, and compilation, bandwidth matters more than latency.

RAM Timing Numbers Explained

RAM timings are listed as four numbers, for example 16-18-18-38. Each number represents a different delay measured in clock cycles:

Timing	Full Name	What It Means	Impact
CL (first number)	CAS Latency	Cycles between a read command and data arriving	Highest impact - this is the one everyone focuses on
tRCD (second)	Row to Column Delay	Cycles to open a row before reading from it	Moderate - affects access to new rows
tRP (third)	Row Precharge	Cycles to close a row before opening a new one	Moderate - affects row switching speed
tRAS (fourth)	Row Active Time	Minimum cycles a row must stay open	Lower impact - often auto-tuned

This calculator focuses on CL (CAS Latency) because it has the most direct impact on real-world performance and is the primary number used to compare kits. Tighter secondary timings help too, but CL is the headline number.

What True Latency Means for Gaming

RAM latency matters most in CPU-bound scenarios - typically gaming at 1080p with a fast GPU. At higher resolutions where the GPU is the bottleneck, RAM speed makes almost no difference.

True Latency Range	Rating	Typical Kits	Gaming Impact (1080p CPU-bound)
Below 8 ns	Excellent	DDR4-4000+ CL15, DDR5-7200+ CL28	Maximum FPS in competitive titles, 3-5% over average kits
8-9 ns	Very good	DDR4-3600 CL16, DDR5-7200 CL34	Sweet spot for gaming - excellent performance per pound/dollar
9-10 ns	Good	DDR4-3200 CL16, DDR5-6000 CL30	Solid performance, most popular kits land here
10-12 ns	Average	DDR4-3200 CL18, DDR5-5600 CL36	Acceptable, but leaving some performance on the table
Above 12 ns	Slow	DDR4-2400 CL17, DDR5-4800 CL40	Noticeable FPS loss in CPU-bound scenarios

AMD vs Intel: RAM Preferences

AMD and Intel platforms respond differently to RAM speed and latency:

Platform	Sweet Spot	Why
AMD Ryzen 5000 (DDR4)	DDR4-3600 CL16	Infinity Fabric runs at 1:1 with RAM clock, best at 1800 MHz (DDR4-3600)
AMD Ryzen 7000/9000 (DDR5)	DDR5-6000 CL30	Infinity Fabric sweet spot at DDR5-6000, going higher can cause 2:1 ratio downshift
Intel 12th/13th/14th Gen	DDR5-6400+ CL32	No fabric ratio limitation, benefits from higher speeds more linearly
Intel Core Ultra (Arrow Lake+)	DDR5-6400+ CL30-32	New memory controller, benefits from fast DDR5

For AMD Ryzen systems, going above the sweet spot can actually reduce performance if the Infinity Fabric drops to a 2:1 ratio. This makes the true latency calculation especially important for AMD builds.

XMP / EXPO: Enabling Rated Speeds

RAM runs at its base JEDEC speed by default - typically DDR4-2133 or DDR5-4800. The higher speeds advertised on the box (DDR4-3600, DDR5-6000, etc.) require enabling an overclocking profile in BIOS:

Profile	Platform	What It Does
XMP (Extreme Memory Profile)	Intel (also works on AMD)	Stores speed, voltage, and timing settings on the memory module's SPD chip
EXPO (Extended Profiles for Overclocking)	AMD (DDR5 only)	AMD's equivalent to XMP, optimised for Ryzen memory controllers
JEDEC	All platforms	The default safe speed - no overclocking, guaranteed stable

If you buy DDR5-6000 RAM and do not enable XMP/EXPO in BIOS, it runs at DDR5-4800 and you are not getting what you paid for. After enabling the profile, run a memory stability test (memtest86+ or TestMem5) to confirm it works reliably with your specific CPU's memory controller.

If you are evaluating a full build, the bottleneck calculator shows how your CPU and GPU pair together. For power supply sizing with your complete build, the PSU calculator covers all components. All calculations run in your browser with no data sent anywhere.