Brief summary: scientists create model based on age, height, weight, sex, race, waist circumference and hip circumference. This is more accurate than the one based on height and weight, and also impossible to use without a computer.
Very usable without a computer once you do it once.
If you're at a 5 on the scale, "average to unhealthy" at 36 inches, you can put in 32 inches and find out that you'll be "lean to average." Or maybe you're a 42 and a 38 to get the same range. It's pretty easy to put in your waist, then set a "goal" waist.
So your goal is to lose 4 inches of stomach width, which you can measure with a $3 tailors tape.
Update the goal every year or so, as the numbers change as you age, but other than that, you're all good.
BMI has some great benefits, in that it's really easy to get and you can't mess it up. That's why it's a great measure for population and an amazing indicator for individuals.
BMI = Heigh / (weight * weight)
anyone who made it halfway through highschool can do this
I had to tripple check if I got the correct number of brackets, that's how easy it is. And note that this isn't even the useful number that's used in the supporting paper. They validate their model by adding in other factors for waist and hip circumferences, age, height, gender, ethnicity, and body weight, to get bodyfat percentage and visceral adipose tissue, and check that to other data.
BMI is a spherical cow in vacuum, simple, easy, and close enough in basically all cases. And when it's off, it's usually off in being too conservative. BRI is a great tool for healthcare profesionals, but it requires too many measurements and too much math for the average person.