Trinny and Susannah's breast-laid plan

Why weighing your boobs in water could be the key to finding the perfect bra

STILL CAN'T FIND the perfect fitting bra? The key could be weighing your breasts in water.

Confused? You aren't the only one. However, Trinny and Susannah (who, let's face it, know women's breasts better than most) claim dunking your boobs in water and weighing them would be a far more accurate way to assess your cup size than the current sales-woman-and-a-tape-measure method we're used to.

'It's astonishing that so many women have no concept of how big their boobs are,' says Susannah, who can be seen on ITV tonight pioneering the technique. 'Hardly anyone has the right size bra on. Bras are either way too big, or way too small.'

Following her experiment, which also involved a set of kitchen scales and a baking tray, design engineer Dr John Tyrer is now crafting her the perfect bra, based on weight, rather than cup size.

'Women have this wonderful methodology about their breasts. They say, "Well, they're different, they're this shape, they're that size." The question is how do you know?' asks Tyrer. 'Because the measurement process you have is an irrelevance.

'If you're an engineer or a designer the first thing you want to know is how heavy - how heavy are each of your breasts.

'Knowing the displaced amount of water tells us what the breast weight is. Then, using a conversion factor we can then convert the weight of displaced water to the weight of the breast.

'We used water displacement because it is a good practical science experiment you could do at home, if you so wished.

'Our techniques have allowed us to pioneer new designs of bras which, unlike existing bra designs, now actually work.'

You can watch Susannah having her breasts weighed on Trinny and Susannah's Undress the Nation on ITV1 at 8pm tonight.