On the IB website it states that the minimum IDEALPRO trade size is $25,000 US. I assume that the trade size you enter in the TWS order dialog is in the selected 'currency' (e.g. JPY for USD.JPY), does this mean the minimum trade size for a IDEALPRO USD.JPY trade is 25000 / (USD.JPY quote)? Have I got this all wrong? If so how does one calculate the minimum trade sizes of different symbols?
No, the size you trade is quoted in the first part of the pair: In USDJPY your order is 25.000 USD. So buy 25000 is going long USD and short JPY. When you buy 25000 at 95.00 and then sell 25000 at 95.10 your net profit is in JPY - your USD account is the same but your JPY account receives 2500 yen.
You can try these kind of things by using the Demo or the Paper Trader. Moreover, it can be found on the website: http://www.interactivebrokers.com/e...?exch=ibfxpro&showcategories=FX&ib_entity=llc