Check the RAM label/sticker on the module
Open Task Manager on Windows and go to Performance > Memory
Use CPU-Z and read the DRAM Frequency
Use BIOS/UEFI and look for memory speed or DRAM frequency
Check system information tools like HWiNFO or Speccy
Look up the RAM model number online
Use Command Prompt on Windows with wmic memorychip get speed
Use PowerShell with Get-CimInstance Win32_PhysicalMemory | Select-Object Speed
Check the motherboard or laptop specifications
Check the purchase invoice or product listing
Compare DDR type with effective speed
Multiply DRAM Frequency by 2 for DDR RAM effective speed