If your taxable income (including the Roth conversion amount) is under $78,950 (Married Filing Jointly), the conversion will be taxed at 12%. $78.950 is the threshold for the next tax bracket (22%).
Taxable income is Adjusted Gross income minus Standard or itemized deductions.
So, if you have $77,000 of other income, you can convert up $26,350 at the 12% rate ($77,000 - 24,400 = 52,600; 78,950 -52,600 = 26,350)
