Waist measurement changing

I don’t really consider myself an XXS but this sub Reddit keeps on showing up in my feed. I see a lot of you putting your waist measurement in your posts. I have no idea what waist size I am because it changes throughout the day. How do you identify your true waist measurement? For example, in the morning before having food and when I’m not bloated I’m a 23”. But during the day, especially after food, and when I’m bloated, I could be up to 27”.