Position size
Risk in money is the balance times the percentage you accept losing. Divide that by what one lot loses over your stop distance:
lots = (balance × risk%) ÷ (stop distance × value per point per lot)
The part people get wrong is the last term: it is not the same for EURUSD, XAUUSD and US30. That is why a “0.10 lots always” habit risks a different amount on every instrument. Worked examples.