Its complicated. You can't always trust given sizes but need actual measurements.
I've handled thousands of suits, jackets, shirts, trousers from different brands and countries of manufacture. Some of these things vary so much, from brand to brand, its hard to make a rule. Many of the fast fashion places, like Zara etc, have such a fast turn around of styles - e.g. 2 weeks that there isn't time to ensure QC consistency of sizes between runs. Which is why they have to have free returns etc on online orders.
To an extent a lot of the "slow fashion" quality manufacturers have the same problem but to a lesser extent. Runs of RTW will go out even if they differ from original specs.
In general stuff for retail in USA is made to "catalogue sizes" where trousers for sale in USA marked size 34 will have a waist of 35" or 35.5". 35" will = 36". Stuff for sale in EU seems usually to be a bit more TTS where a 87cm will be 87cm (34.25"). This is irrespective of where its actually made.
And then you have the translation from USA/UK sizing in inches to the rest of the world in metric. Often in OZ you have both. Translating to metric usually goes to the nearest .cm which in the case of a 34" trouser is actually 86.5cm but will usually go to 87cm which is really 34.25" so in effect suggesting a trouser marked 87cm is a 1/4 of an inch larger than it is.
Now to make it even more complicated: If its a trouser for a USA retail marked 34" size but actual measurements are 35.5" it will be converted to .cm from 34" - so it will me marked as a 86cm or 87cm. When in reality it actually measures 90cm- 91cm.
The same thing to various degrees occurs with shirts and suits. Shirts - 16" = 40.75cm, 16.5" = 42cm, 17 = 43.20cm. But you will only see 41, 42, 43 in shirts.
Its a jungle out there
in ready to wear
makes me wonder
how I keep from going under.
