If you have a $1,000 account and your trading plan has a max risk of 2% per trade you are only able to risk $20 per trade.
To stay within this risk rule you need to either adjust your stop loss in pips or your lot size. Most often adjusting the lot size is the better option since a stop loss should be placed where market structure dictates.
$20 risk at 10 pip SL = 0.2 lot size
$20 risk at 20 pip SL = 0.1 lot size
$20 risk at 25 pip SL = 0.08 lot size
$20 risk at 40 pip SL = 0.05 lot size
$20 risk at 50 pip SL = 0.04 lot size
Formula: (max risk $ amount ÷ SL # of pips) x 0.1 = appropriate lot size