Position Sizing (การกำหนดขนาดไม้)
Position Sizing is choosing how big a trade is, such as its lot size, so that a Stop Loss hit costs only the amount you planned to risk.
Position Sizing means deciding how large a trade should be before you open it. Instead of picking a lot size by feel, you start with the amount of money you are willing to lose on that trade, then work backwards to the lot size.
The basic steps
- Decide your risk per trade, often a small percentage of your account.
- Decide where your Stop Loss will go, measured in pips.
- Use this formula:
Lot size = Risk amount ÷ (Stop Loss in pips × pip value per lot)
Example
You have a $1,000 account and choose to risk 1%, which is $10. You plan to trade EURUSD with a Stop Loss 20 pips away. For a USD account, one standard lot (1.00) is worth about $10 per pip.
Lot size = 10 ÷ (20 × 10) = 0.05 lot
Check: 0.05 lot is about $0.50 per pip. If price moves 20 pips against you, the loss is 20 × $0.50 = $10, which is the amount you planned.
If you used a wider 40 pip Stop Loss, the lot size would be 0.025 lot. A wider stop means a smaller position for the same risk.
Why it matters
Position Sizing keeps each loss at a size you chose. A common beginner mistake is using the same lot size every time, whatever the Stop Loss distance. Another is moving the Stop Loss further away just to keep a big lot size. Pip value differs between pairs and account currencies, so check it before you calculate.