Hi Baz !
Thanks for your kind help. You have always answered my weird questions and helped me with forex mathematics. Since in many previous posts, you have emphasised the babypips calculator so I’ll talk in detail about this lot size thing here. My purpose is not to offend you at all :). Its just different mind set and theory.
First of all, this is not set in the stone that we should determine our lot size based on Risk % Method. There are other methods too, which I’ll talk about here later in the post. But first let me deal with my example and I’ll attach Babypip’s and Oanda’s calculator (calculations) here as well.
With $1,000 USD in my account, If I want to risk 20% of my account on a particular trade with 50 pips stop loss, the babypips calculator shows 40,000 units (see attached pic)
Now here’s Oanda’s Order Window:
So now let’s compare these two:

The Oanda’s calculator (basically order window), you can see we cannot enter the trade based on 40,000 units, which should be lot size according to Babypips Calc.

The Margin used is more than the account size actually.
The method I use, which may sound inappropriate and insane to many here, is based on margin %. I always want to use 20%. If you apply the same 20% to units available, and then calculate the margin, it also boils down to 20% (I’ll doublecheck it twice to confirm when the price changes).
The leverage is the key here, which allows us to control higher value trade.
With $1,000 USD and 50 Leverage and EUR/USD at 1.2850, total units available are 38,910 units.
= [( $1,000 USD x 50 Leverage )/1.2850] = 38,910 units
I will want to use 20% of total units available, i.e. 7,822
Does this also mean that we are using 20% margin (meaning margin is 20% of our account size) ?
Lets check:
= [(7,822 units x 1.2850)/50 Leverage] = $201 USD, which is almost 20% of our account. So here I have confirmed it.
So the main thing is that:
 Risk % method is not the only method to determine the lot size.
 Leverage does determine the lot size and lot size determines the margin and pip value and hence profit.
I may be wrong and a lot of traders here may take me as a superdooper idiot or whatever. But I made my point. This is not to offend or falsify anyone, just my own calculations.
Thanks for your help as always
Your kind comments and corrections are most welcome and will be highly appreciated
Thanks