Roth conversions

Dear Terry,
I am a very fortunate 72 years old, retired with a pension, waited until 70 to collect social security and have taxable investments. I have a very large IRA (many millions) and am exploring a large Roth conversion. Is there a calculator that advises the amount to convert taking into account IRMAA, IRS tax brackets ,etc. I am leaning toward converting the entire IRA, taking a huge tax/IRMAA hit for one year and then making it up by investing the Roth and letting it grow tax free.