What is RAM latency?

RAM latency, often called CAS latency (Column Access Strobe latency), measures the delay between when a memory controller requests data and when that data becomes available. It's expressed in clock cycles (e.g., CL16, CL18) and represents how many cycles the RAM must wait before responding to a read command.

Lower latency means faster memory response times, but the actual speed depends on both the latency value and the RAM's operating frequency. A higher-frequency RAM with slightly higher CAS latency can still outperform slower RAM with lower latency.

How is RAM latency calculated?

The true latency in nanoseconds is calculated using this formula:

Latency (ns) = (CAS Latency × 2000) ÷ RAM Speed (MT/s)

This formula accounts for DDR (Double Data Rate) memory, which transfers data twice per clock cycle. The "MT/s" (Megatransfers per second) rating you see on RAM specifications is double the actual clock frequency.

For example, DDR4-3200 RAM with CL16:

  • Latency = (16 × 2000) ÷ 3200 = 10 ns

Why does RAM latency matter?

RAM latency directly impacts system responsiveness, especially in:

  • Gaming: Lower latency reduces frame time variations and improves minimum FPS
  • Content creation: Faster memory access speeds up rendering and processing
  • Everyday computing: Applications load and respond more quickly
  • Ryzen CPUs: AMD processors are particularly sensitive to memory latency due to their Infinity Fabric architecture

What's the difference between MT/s and MHz?

MT/s (Megatransfers per second) represents the data transfer rate, while MHz represents the actual clock frequency. DDR memory transfers data on both the rising and falling edges of the clock signal, so:

Effective Clock (MHz) = MT/s ÷ 2

DDR4-3200 operates at 1600 MHz but achieves 3200 MT/s due to double data rate technology.

Tool description

This RAM latency calculator converts CAS latency (clock cycles) to true latency in nanoseconds. Enter your RAM speed and CAS latency to instantly see the actual memory response time. The tool also displays the effective clock frequency and cycle time for deeper technical analysis.

Examples

RAM Type Speed (MT/s) CAS Latency True Latency
DDR4-2133 2133 CL15 14.06 ns
DDR4-2400 2400 CL16 13.33 ns
DDR4-3000 3000 CL15 10.00 ns
DDR4-3200 3200 CL16 10.00 ns
DDR4-3600 3600 CL16 8.89 ns
DDR4-3600 3600 CL18 10.00 ns
DDR5-5600 5600 CL36 12.86 ns
DDR5-6000 6000 CL30 10.00 ns
DDR5-6400 6400 CL32 10.00 ns

Features

  • Preset RAM speeds: Quick selection for common DDR4 and DDR5 configurations
  • Custom speed input: Enter any RAM speed for overclocked or non-standard memory
  • True latency calculation: Converts CL cycles to nanoseconds
  • Effective frequency display: Shows actual clock speed in MHz
  • Cycle time calculation: Displays time per clock cycle in nanoseconds

Use cases

  • Comparing RAM kits: Determine which combination of speed and CAS latency provides lower true latency
  • Overclocking decisions: Calculate whether increasing frequency or tightening timings yields better results
  • Purchase planning: Compare advertised specs to find the best-performing RAM for your budget
  • System optimization: Verify your RAM's actual performance matches expectations
  • Technical documentation: Get precise latency values for system specifications