Most losing traders size every trade the same way — 100 shares of every stock, or 1 lot on every forex pair. The size doesn't relate to where the stop is, how volatile the market is, or how much the account has grown. This is why drawdowns feel random and uncontrollable: because the risk on each trade actually is.
Proper position sizing fixes this. It makes the dollar risk on every trade the same regardless of price, stop distance, or instrument.
The Formula
Two steps:
- Dollar risk = Account size × Risk %
- Position size = Dollar risk ÷ Risk per unit (per share, per pip, per coin)
Example: $20,000 account, 1% risk = $200 dollar risk. Entry $50, stop $46, risk per share $4. Position size = $200 ÷ $4 = 50 shares. Total exposure = $2,500.
For Stocks
Risk per share = Entry price − Stop loss price.
Example: $15,000 account · 1% risk ($150) · Entry $120 · Stop $114 · Risk per share $6 · Position = $150 ÷ $6 = 25 shares · Position value = $3,000.
A wider stop means fewer shares. A tighter stop means more. The dollar risk stays fixed at $150 either way. This is the core idea: position size adapts to the stop, not the other way around.
For Forex
Convert pips to dollars using the pip value for your lot size. Position = Dollar risk ÷ (Stop in pips × pip value per lot).
Example: $10,000 account · 1% risk ($100) · 25-pip stop · EUR/USD mini lot pip value = $1 · Position = $100 ÷ (25 × $1) = 4 mini lots (0.4 lots).
The Lot Size Calculator does this calculation directly in pip terms.
For Crypto
Works identically to stocks. Use your buy price as entry and your planned stop as exit. The result is in fractional coins — for example, 0.05 BTC. Multiply by price to confirm the position value fits your sizing rules.
Why the Risk Percentage Matters More Than You Think
After 5 consecutive losses — a normal run for any strategy with a 50% win rate — here's the damage at different risk levels:
- 1% per trade: account down 4.9%, need 5.1% to recover
- 5% per trade: account down 22.6%, need 29.2% to recover
- 10% per trade: account down 40.9%, need 69.2% to recover
This is why professionals risk 0.5–1% per trade. Not conservatism — it's about staying in the game long enough for an edge to play out over hundreds of trades.
The Most Common Mistake
Traders decide how many shares they want to trade and then set a stop to limit the loss to an acceptable dollar amount — backwards from what they should be doing. The correct sequence is: identify the technical level where the trade is invalidated, place the stop there, then calculate the position size that keeps the dollar risk within your limit. The chart tells you where the stop goes. Your risk rules tell you how many shares to trade.