How much money in deductions do I need to take the itemized deduction?

Single or Married filing separately—$12,400.
Married filing jointly or Qualify-ing widow(er)—$24,800.
Head of household—$18,650.

the above are higher if the taxpayer/spouse is blind or over 65.

all these are after any limits imposed by the tax laws - examples - medical expenses are only deductible to the extent they exceed 7.5% of adjusted gross income.  taxes are limited to $10,000, mortgage interest can be limited if the acquisition debt exceeds the maximum for your situation

if you are a dependent standard deduction can not exceed the greater of $1,100 or the sum of $350 and your individual earned income. Additionally, this rule does not apply if the dependent makes equal to or greater than the standard deduction for their filing status.

additionally, if married filing separate both must use the same - either itemized or standard deduction.