In that case the Form 1099-R that you received from the plan for the distribution from the traditional 401(k) account should have the same amount in box 5 as is in box 1 and box 2a should have a zero for the taxable amount. Simply enter this Form 1099-R and answer the follow-up questions to indicate what you did with the distribution. If the Form 1099-R has code G in box 7 indicating a direct rollover, simply indicate that the rollover was to a Roth 401(k) and TurboTax will treat it as nontaxable. You should see the gross amount included on Form 1040 line 4c but see it excluded from the taxable amount on line 4d, with the word ROLLOVER next to the line.
