hi cetanu, i have no idea to be honest, will give them a ring and find out for you. The are designed to be worn skin tight though, like the nike pro vent tops, as they pour sweat away from your body, so if your chest is a medium, then i would go for that, as it will fit your chest and be tight on the legs, but not tight enough to hurt/rub or cut your circulation off.
if anyone is interested, they charge be £6 postage next day for orders under £150, then i would have to post it out to you, so say, £3 and paypal fees...so...stick £10 on top of the price if you want them, or if i get 6 people that want a set, postage will be £1 each etc....