It depends on whether you have any pre-existing pre-tax money in your IRA(s). If there is none, then the conversion is 100% nontaxable because it consists of 100% nondeductible basis from your traditional IRA. If you have existing pre-tax IRA money, then the conversion has to be a proportional mixture of pre-tax and after-tax (nondeductible) amounts, and is taxable in the same proportion.