Hi,
Can anyone help me out here with how reliable this is? My sons worried as he’s put his numbers into a calculator that uses neck and waist measurement - the US Navy method apparently - which tells him he’s 3% BF…somewhat unlikely
He’s grasped that BMI is inaccurate, which I agree, but believes this method to be accurate. If I can explain why it’s inaccurate I’ll be able to reassure him.
The “you’d be dead?” is not sufficient to explain the inaccuracy?
It takes very careful explanation to convince him of things, which in general would be a good thing, but unfortunately tends to mean that he rejects the obvious in favour of the dramatic.
So no, I need to figure out why the calculator is showing bollocks 
Looking at the formula it seems very sensitive to large neck sizes, it is quite simplistic
If you can ‘pinch an inch’.
It’s all mostly bull. All are different. It’s like fad diets, all bull. And this comment is utterly useless as an answer to your question, sorry on that point. Back to cooking lunch.
I know nothing of this method but below 4% or so, the myelination around the nerves is greatly reduced and really affects their fnction. Not to mention the hormonal disfunction that would be going on.
When boxing as yoof - young man I got below 5% and my skin was paper thin. To say BMI is inaccurate is unfair IMHO, as it for most people it’s a good guide. If you’re very muscular or endurance athlete (healthy) thin then sure it might say you’re at an unhealthy weight when you’re not. But if you’re in one of those groups then you’re unlikely to be unaware of that so why would you be interested in BMI?
Just used the calculator. It’s weird I put my values in and it gives me 16% fat but then I change the weight by 10lbs and the fat % remains the same. That’s moving it up or down. I suspect that like BMI, as the population of users grow the accuracy overall goes up (if that makes sense). This is the fattest I have ever been 
The mirror values in this link are ball park right IMO and good enough for most I reckon. https://www.nerdfitness.com/blog/body-fat-percentage/
Does he look like he survived a Japanese POW camp? 
Seriously though, show him a picture of a POW from WW2 and tell him they have more than 3% and you have your dramatic visual explanation of why it’s utter bolox.
I should have asked; what’s the goal of all this? Does he need to know his BF for a specific reason, or is he just doing it out of curiosity/boredom or vanity?
If it’s just about fitness, I remember seeing an article about 30 years ago about long distance triathletes; it was titled "don’t let a few extra lbs fool you" and it’s right. Skinny isn’t always healthy.
Very roughly it makes me 18.8% and says I need to lose 1kg of fat. Again I put my IM race weight in, where I am gaunt, and it still says 18.8% and I need to lose 1kg of fat 
It says my BMI would be 21.8 then 20.8 when I change my weight. It doesn’t even put me in the ‘fitness’ category, and yet I can run sub 5:00/kms in my sleep.
Strikes me as another calculation that’s about as blunt as a barge pole.
you mean you’re not even fast in your dreams??? 
I haven’t tried sub 4 of late; don’t really feel like it at 0630, or with a 40lb bergen 
Last time I had a quick hit-out was after a swim last autumn; did 2km fast during a run, to see if I could pass the (new) Army standards. Suffice to say, comfortably under 8 mins.
Oh sorry, I forgot, you dropped this 
firstly, how old is he?
Secondly, it looks like this method is designed to stop sailors rolling off ships…if i had time i’d like to put some of my ex-Reg mates through it (those with the Mike Tyson necks)…
if he is of age, and there is genuine concern, then a decent body composition monitor could be useful…
Is that the standard? That’s two thirds of the army gone then???
I used that one in “nutrition” group as to why its bollocks that you can get fat by undereating and that it isnt bottom line calories in v calories out. Apparently that was an extreme example and the general population isnt like that. i left that group.
Nope! What I meant was that I’d clipped off two sub-4s; I will have a quick look to see what the stds are nowadays. I’m pretty sure Para Regt is sub 8:15 on entry, which is the highest std.
ok, it was 9:30 for 1.5 miles in boots as entry iirc…
No he’s physically healthy, its just a case of explaining why this calculation is incorrect.
Looks like there’s a complete overhaul underway, with Role specific tests (as part of MATTs) taking the place of the usual ‘sports kit’ tests.