The Body Mass Index is completely evil. It tells hundreds of millions of people that they’re fat and unhealthy, even if they’re not.

The BMI’s a quick, easy way of calculating how overweight you are. Everybody uses it because it’s simple. It’s on government sites like the NIH.

And it’s evil. It is designed to make you think you’re overweight. Or way overweight than you really are.

No, that’s not right. The BMI was designed, 150 years ago, to gauge the average fat percentage of a large population of European white males. For purposes of broad studies of a population’s health. (And in days when food could be hard to come by, a little fat was a positive thing.)

So it’s not the BMI that’s evil. It’s the doctors who tell you to worship it. They’re fairly ignorant about nutrition, and the BMI gives them an easy out to say, “You should lose some weight.” Without knowing what they’re talking about.

Here’s a case in point: I lost 50 pounds over the past year because I had to stay home and eat healthy food. I’m six feet tall. I’ve got pecs and big arms. I wear pants with a 36-inch waist. You can see my veins. And the BMI says I’m overweight. Nah. Just nah.

Now, I have been very overweight, and also very light. I’ve seen my body change. My experience has given me insight on a far, far better snap weight calculation than the miserable BMI. I’ve tested it from experience, and it works on half the human population of the globe. I call it:

WHERE’S JOHNSON?

I’m a guy. I have a penis; I prefer the slang term “Johnson.” If I get naked, stand up straight and look straight down, I can see my limp Johnson in top profile: a sort of lump that sticks up an inch/inch-and-a-half over the general contour of the bod.

But as I put on more fat my belly grows — that’s where men put it — and it increasingly blocks the view of my pubes, and my Johnson.

You see where I’m going, right? My Johnson and the pubes above it, are a sort of dipstick for body fat. The less pube and Johnson you see, the more overweight or obese you are. Simple, right? Useful? I think so.

There are no calculations. Everything’s relative to your own size and height.

Okay, if you regularly lift extremely heavy objects your belly may thicken from muscle alone but that’s what, 2 percent of the population? And you know who you are.

So, if you have a Johnson, it’s time to:

1. Strip naked.
2. Stand erect with shoulders squared but not thrown back.
3. Look straight down, and…
4. Ask the question: “WHERE’S JOHNSON?

Well, where is Johnson? The answer is one of these:

I CAN’T SEE JOHNSON! You’re quite obese. You’re wearing a nice thick overcoat of fat, unless that thick gut is all muscle. Or you have a microjohnson. Sorry.

I CAN SEE PART OF JOHNSON! This was me at 260. I was carrying a lot of muscle, but I could have stood to lose 50 pounds or more. Call it less obese.

I CAN SEE ALL OF JOHNSON, BUT NOTHING ABOVE IT! If you can see all of Johnson but you gut overhangs the rest of your pubes, you’re pretty overweight but probably not obese.

I CAN SEE ALL OF JOHNSON AND SOME OF MY PUBES. You’re average-overweight. You could probably stand to lose a fair amount of weight — like most of the rest of the population.

I said, “probably.” If you can see pubs and abs above Johnson, you need to fine-tune the results with a hand measurement:

1. Lay the forefinger of your left hand (or your right, if you’re a lefty) straight across the root of your Johnson.
2. Slide your thumb up your abdomen until the bulge of your belly begins to hide your thumbnail.
3. Hold your thumb and forefinger in that position and examine their position relative to each other. The closer together they are, the fatter you are.

HOW ABOUT THIS CLOSE?

That close together? You could stand to lose some. Truly.

HOW ABOUT FARTHER?

CONGRATULATIONS! YOU’VE attained FLAB! Yeah, you’re in the normal range. You’re just not lean; you don’t look like an athlete. Who cares?

HOW ABOUT EVEN FARTHER THAN THAT?

You’ve got a flat belly, except for the natural bulge of the stomach muscle and a bit of healthy pudge. You’re a 20-year-old with a nuclear metabolism. Or, you eat way too healthy and fast 16 hours a day or run 20 miles a week. Feel free to not do this.

Everybody’s built different, so all the proportions used in this test are relative: including the size of your hand, your belly, and your Johnson. If you’re smaller, they’re usually smaller, too, in absolute terms.

WHERE’S JOHNSON is imperfect. But who could argue that a missing Johnson is a sign of trouble? Or that a near- unobstructed view of Johnson and your pubes is a rare and precious thing. And a luxury.

So, strip. And learn something. Hey, JOHNSON!