Lot size is the volume of a single trade, and choosing it correctly is the core of risk management. Instead of picking a number at random, sized trades work backward from how much you are willing to lose: account balance, risk percent, and stop-loss distance together decide the right lot size. Getting this right keeps every losing trade survivable.
On a $5,000 account risking 1% ($50) with a 50-pip stop on EUR/USD, the safe size is about 0.10 lots — small enough that a full stop-out costs only $50.
This definition is for educational purposes only and is not financial advice. Trading involves risk.