What is the ideal concentration of MgCl2?

Ideal concentration of MgCl2 in PCR mixtures is within the range of 1.5 to 4.5 mM. 

Using the correct concentration of MgCl2 is important for optimizing PCR protocols. Higher or lower concentrations provide inaccurate results. Too much MgCl2 increases the chances of non-specific primer binding, leading to errors in DNA replication. Too little MgCl2 can result in weak amplification or total PCR failure as primers are unable to base pair with the DNA template at low MgCl2 concentrations.