How to calculate the capital used for first entry

Does anyone have a way to calclulate an entry for scaletrading ? I would like to know if anyone have a smart way of calculated the right entry size for scaletrading. If i buy a currency pair at a given price and i want to add to the position with the same amount at each trade does anyone have a smart way to calculate how many times i can add if my starting lot is xxx. I would like to find out at what lvl i will be at a loss of 25 pct of my capital. Or at what lot size i will have lost 10 pct and how many times i have added and how many percent the price have moved from my entry price.

Tnx in advance

figure out the stop loss in pips and money and never more than 2 or 3 % per trade,adjust your lot size from that point