Per The Internal Revenue Service:
You MUST take your first RMD by April 1 of the year following the year in which you turn 72 (70 ½ if you reach 70 ½ before January 1, 2020) regardless of whether you are still employed.
Your RMD is generally determined by dividing the ADJUSTED MARKET VALUE OF YOUR IRAs as of December 31 of the preceding year by the distribution period that corresponds with your age in the Uniform Lifetime Table (Table III in IRS Publication 590-B, Distributions from Individual Retirement Arrangements (IRAs)).
If your spouse is your sole beneficiary and is more than 10 years younger than you, you will use the Joint Life and Last Survivor Expectancy Table (Table II in IRS Publication 590-B).
Joint Life and Last Survivor Expectancy & Uniform Lifetime Tables