Position sizing: how traders limit the risk of a single trade

Many beginners ask "how much should I buy?". Traders usually turn the question around: how much am I willing to lose if I am wrong?

The three numbers

• Account size — the money set aside for trading.
• Risk per trade — the share of the account you accept losing on one idea. Many educational sources use small percentages for this, so that a series of losses does not wipe out the account.
• Stop distance — how far the price can move against you before you exit.

Position size follows from them:

position size = (account size × risk per trade) ÷ stop distance

A worked example

Suppose an account of 1,000 USDT, a risk of 1% (10 USDT) and a planned exit 5% below the entry price. The position can then be about 200 USDT: a 5% fall on 200 USDT is 10 USDT. If the planned exit were 2% below the entry, the same risk would allow a larger position.

The numbers are illustrative. The point is the relationship: a wider stop means a smaller position for the same risk.

Why it matters

• A long losing streak happens to everyone. Small, fixed risk keeps it survivable.
• Deciding the loss in advance removes some emotion from the decision.
• Leverage does not change the logic — it only makes the position bigger relative to the margin, so mistakes cost more.

Common mistakes

• Increasing size after losses to "win it back".
• Moving the exit further away when the price approaches it.
• Ignoring fees and slippage, which make real losses larger.

This is general education. XFasil does not provide trading operations or investment advice; the Spot and Futures screens show market data only.