Lot size calculator
Your lot size from the money you are willing to lose and where your stop is. For forex pairs, gold and silver, with your prop firm's daily limit in view.
See TradeWarden
Want it on your MT5 chart? The free position size indicator does the same from a stop line you drag, with your broker's own tick value.
How it is calculated
One lot loses the distance between your entry and your stop, times the contract size, converted to US dollars. The lot size is your risk divided by that, rounded down to 0.01 lot so the real risk never goes above what you chose. When the price is not quoted in dollars (USDJPY, EURJPY, USDCHF, USDCAD, EURGBP) the loss is converted with the pair's own price, or with the European Central Bank's reference rate for crosses (latest working day).
Questions
How do I calculate lot size from my risk?
Divide the money you are willing to lose by what one lot loses if your stop is hit. One lot loses the distance between entry and stop times the contract size (100,000 units for a standard forex lot), converted to your account currency. Round down to your broker's lot step, usually 0.01.
What is the lot size for gold (XAUUSD)?
On many MT5 brokers one lot of XAUUSD is 100 ounces, so each $1 move in the gold price is $100 per lot. Brokers differ, so check the contract size in MT5: right-click the symbol in Market Watch, then Specification.
How much should I risk per trade on a prop firm challenge?
That is your decision, but compare it with your firm's daily loss limit. On FTMO 2-Step the daily limit is 5% of the initial balance, so at 1% risk five full losses in one day use up the whole limit; at 2.5% it takes two. See every firm's limits and the drawdown calculator.