Converting IRA to Roth to save on taxes

I understand 2024 tax rate is 12% up to $94,300. My adjusted gross income for 2023 was 85,760 and taxable income was $48,012. Year 2024 income will be slightly less. Is that 12% tax threshold based on the AGI or taxable rate?

Based on 2023 income, how much could I convert before going over 12% bracket?

Thank you.