RAM Latency Calculator
Convert CAS latency (CL) and memory speed (MT/s) into real nanoseconds: ns = (CL × 2000) / MT/s. Compare DDR4 vs DDR5 kits fairly — CL alone is misleading when clock speeds differ.
Kit A
True latency 10.00 ns
Kit B
True latency 10.00 ns
Compare
Lower first-word latency (ns) = faster CAS access. Higher MT/s raises peak bandwidth even when ns is similar.
| Metric | Kit A | Kit B |
|---|---|---|
| Memory speed (MT/s) | 3200 | 6000 |
| Cycle time (ns) | 0.625 | 0.333 |
| CAS cycles | 16 | 30 |
| First-word latency (ns) | 10.00 | 10.00 |
| Peak bandwidth (GB/s) | 25.6 | 48.0 |
Reverse: target latency → required CL
Required CAS latency: CL 36(actual 10.00 ns at integer CL)
How to use
- Enter Kit A and Kit B memory speed (MT/s) and CAS latency (CL), or click a preset (DDR4 / DDR5 kits).
- Read True latency in nanoseconds for each kit — lower ns means faster first-word access.
- Use the Compare table for cycle time, CAS cycles, latency, and theoretical peak bandwidth.
- In Reverse, enter a target ns and MT/s to get the minimum integer CL required.
- Use Copy results when comparing kits for a build or upgrade post.
FAQ
Why do DDR5 kits have higher CL numbers?
CL counts clock cycles. DDR5 runs much faster MT/s, so each cycle is shorter in nanoseconds. DDR5-6000 CL30 is often ~10 ns — similar to DDR4-3200 CL16. Always convert to ns before comparing.
Is lower nanoseconds always better?
Usually for gaming and latency-sensitive work. For bandwidth-heavy tasks (rendering, compile, video encode), higher MT/s with slightly higher ns can win because throughput matters more.
What is the Ryzen 7000/9000 sweet spot?
DDR5-6000 CL30 (EXPO) is widely recommended: ~10 ns first-word latency and a 1:1 Infinity Fabric ratio on many AM5 boards. Very high MT/s can force half-speed fabric modes that erase gains.
What does the reverse mode do?
Given a target access time (e.g. 9 ns) and speed (e.g. 7200 MT/s), it calculates the minimum integer CL: ceil(ns × MT / 2000), then shows the actual ns at that CL.
Does this test my physical RAM?
No. This is a math calculator only. Hardware stability testing requires tools like MemTest86 outside the browser.
What is peak bandwidth in the table?
Theoretical GB/s for a 64-bit channel: MT/s × 8 / 1000. Dual-channel kits in stores often list doubled marketing bandwidth; this row is per-channel theory.
Introduction
RAM Latency Calculator converts CAS latency (CL) and memory speed (MT/s) into real-world nanoseconds so you can compare kits fairly — e.g. DDR4-3200 CL16 vs DDR5-6000 CL30.
Core formula (first-word / CAS latency):
ns = (CL × 2000) / MT/s
Cycle time per transfer:
t_cycle (ns) = 2000 / MT/s
Higher CL on paper does not always mean slower access when MT/s is much higher.
How the calculator works
Kit A and Kit B
Enter MT/s and CL manually or use presets:
| Presets | Examples |
|---|---|
| DDR4 (Kit A) | 3200 CL16, 3600 CL18, 3600 CL16, 4000 CL18 |
| DDR5 (Kit B) | 5200 CL40, 6000 CL30, 6400 CL32, 7200 CL36, 8000 CL38 |
Compare table
| Metric | Meaning |
|---|---|
| Memory speed (MT/s) | DDR data rate (megatransfers per second) |
| Cycle time (ns) | 2000 / MT/s |
| CAS cycles | Your CL input |
| First-word latency (ns) | (CL × 2000) / MT/s — primary comparison axis |
| Peak bandwidth (GB/s) | MT/s × 8 / 1000 (64-bit channel theory) |
Reverse solve
Given target latency T ns at speed M MT/s:
CL_required = ceil(T × M / 2000)
The tool shows actual ns at that integer CL (may be slightly below target).
What this measures
| Measured | How |
|---|---|
| CAS first-word latency (ns) | Standard DDR formula |
| Relative kit comparison | Side-by-side A vs B |
| Theoretical peak GB/s | From MT/s only |
| Required CL for a latency budget | Reverse mode |
What this does NOT measure
| Not measured | Why |
|---|---|
| tRCD, tRP, tRAS | Not in this simple model |
| Dual-channel multiplier | Shown as single-channel theory |
| On-die ECC, subtimings | Manual inputs only |
| Real game FPS or bench scores | Physics / software dependent |
| RAM hardware defects | Use MemTest86 boot test |
Safety
Pure calculator — no stress, no data sent to servers.
Common use cases
1. DDR4 vs DDR5 shopping
Compare CL16 DDR4 against CL30+ DDR5 on nanoseconds, not cycle count alone.
2. Tightening manual timings
Use Reverse to see what CL you need at your stable MT/s to beat 10 ns.
3. Bandwidth vs latency tradeoff
Same ~10 ns on two kits — pick higher MT/s if your workload is bandwidth-bound.
Related tools
- Memory Test — browser JavaScript heap, not hardware RAM.
- Byte Calculator — storage size units (GB vs GiB).
- CPU Stress Test — CPU throughput stress in the browser.
- Device Info — coarse
deviceMemoryhint from the browser (not CAS timings).