A true gent never asks and a lady never tells. This received wisdom applies to a woman's age, number of sexual partners and, notably, her weight. Only, in the latter scenario, it's not that a woman will never tell, rather that she will always tell a lie.
Admit it, just as men often add an inch or two to their apparent height, women drop a few pounds from their weight when the question is broached.
It's silly and, ultimately, self-deluding behaviour, but we have all, at some point, been guilty of it.
Approaches vary: the ambitious among us will quote their ideal weight, ie the weight they were when they slimmed into their wedding dress or after that awful dose of glandular fever (age 16). The more rational will round down to the nearest stone and justify it inwardly (time of the month/weighing scales a bit dodgy/'bad' week).
This leads us into dangerous territory. If most women lie about their weight, then the rest of us are trying to measure up to illusory ideals.
I used to lie about my weight because I used to listen to other women of the same height who claimed to be "eight stone something".
Worse, I'd read tabloid magazines which "sensationally revealed" celebrities' weights -- generally seven stone something. A quick comparative tally led me to deduct that I was absolutely enormous. It didn't help that the only celebrities who weighed the same as me were Manny Pacquiao and Amir Khan -- championship boxers. The latter is better known as King Khan, which left me fighting with all manner of visual comparisons.
I'm five foot eight and weigh 10 stone (size 10/12) and -- give or take a few pounds.
I hasten to add that I looked ill (and was told as much by all around me) when my weight dropped to nine stone during a stressful period in my life. At nine stone, my rib cage and pelvic bones were visible through my T-shirts, which made me realise that I was by no means overweight at 10 stone and these 'eight stone something' women were, in fact, big fat liars.
Study after study has revealed that weight is the subject women lie about most often, even on official documents and medical questionnaires.
According to a recent UK survey, 59pc of women have told friends and colleagues that they were one size slimmer than they actually were and three-quarters of women said they had lied about their weight in the past.
I decided to do my own study when a friend later told me she weighed eight stone. I asked her to step on the scales (read: dragged her kicking and screaming into the bathroom). The dial arrived at nine stone and seven pounds. We aren't really friends anymore.
Neither should we place any weight on what celebrities apparently weigh. Celebrities very rarely admit their weight and magazine editors grossly under approximate when they guesstimate.
Thankfully, a small group of celebrities have become more forthcoming. Take Katy Perry. Sources estimated that she weighed between eight stone eight and eight stone 11 pounds. She recently admitted that she, in fact, weighs nine stone four pounds: "I was shaped like a square at one time . . . I'm around nine stone four pounds, which is totally fine for me," she said. "When I was a kid, I was the same height and weighed more like 10 stone five pounds."
A recent magazine article speculated that singer Rihanna weighed eight stone 11 pounds. They were 10 pounds out. According to the woman herself: "I'm five foot eight inches and weigh around nine stone seven pounds."
And it isn't easy. She works out every day and her diet consists of "egg whites and pineapple with hot water and lemon for breakfast, fish and potatoes for lunch and fish for dinner."
Kate Winslet (five foot six) considers 10 stone a "sensible weight" and actress Andie McDowell (five foot eight) is "about nine stone 11 pounds to nine stone 12 pounds". She was nine stone six pounds in her modelling days.
Notice that these weigh-ins are nowhere near the weights that magazines estimate, and remember that these women may even be among the 75pc of women who admit to lying about their weight.
Knowing that celebrities ritually discount their actual weight, the producers of reality TV show, Celebrity Love Island, asked all of the female contestants to step on the weighing scales.
Model Sophie Anderton claimed to be eight-and- a-half stone. The dial arrived at nine stone six pounds (all bar one of the female celebrities weighed more than nine stone).
"Last time I weighed myself I was six stone," she snapped. "I don't give a f***, I don't weigh myself, I will be fine when I get a tape measure. When I was 16 I was a size 10 and now I am a size 6."
Personal trainer Pat Henry, who has worked with countless celebrities, agrees that women often reduce their actual weight: "They don't want anyone to know their real weight, actually. They think 'my boyfriend might think I'm fat'."
There seems to be a shame attached to admitting our actual weight, even if it is just a couple of, frankly, meaningless digits.
"Many women are embarrassed, others feel too guilty to admit it and some simply deny it," says Jan Dowling, of Motivation Weight Management Clinic. "The latter won't admit their true weight to themselves as doing so would mean they might have to face up to it and do something about it.
"Some women feel pressure coming from the media and the fashion worlds compelling them to lie about their weight in order to fit in to a perceived ideal."
All women are built differently and most fitness instructors and nutritionists would advise women who don't need to lose excessive amounts of weight to do away with the scales and focus on inches.
Compare this to the skeletally thin Cheryl Cole, who wasn't happy when she couldn't fit into a pair of size 28s.
"I remember being in Selfridges and taking these size 28s into the changing room and not being able to get them on, and then getting on the scales and crying because I was nine-and-a-half stone. Nine-and-a-half stone when I'm only five foot three inches." Most women would shed tears -- tears of joy.
There is no touchstone or benchmark where weight is concerned and no ideal weight for height. More to the point, most women are economical with the truth when it comes to the dreaded question. The weighing scales don't tell the whole story, and most women just make the story up.