What Is Position Sizing in Trading?
Position sizing is the process of deciding how many shares, lots, or contracts to trade on a given position, based on your account size, the trade’s stop-loss distance, and how much capital you are willing to risk. It is the mechanism that turns a trading idea into a specific, risk-controlled trade rather than a guess.
Formula
Position Size (Quantity) = Account Risk (₹) ÷ Stop-Loss Distance per UnitWorked example
A trader with a ₹5,00,000 account decides to risk 1% of capital per trade, which is ₹5,000. They want to buy a stock at ₹500 with a stop-loss at ₹480 — a distance of ₹20 per share.
Position size = ₹5,000 ÷ ₹20 = 250 shares. If the stop-loss is hit, the loss is exactly ₹5,000 (1% of the account), regardless of how far the stock’s price itself moved — the position size was calculated specifically to control that outcome.
What's a good number?
A common range among disciplined traders is risking 0.5% to 2% of account equity per trade. Below 0.5% is very conservative and typically fine for beginners still building consistency. Above 2-3% per trade starts compounding drawdown risk sharply during a losing streak, and above 5% is generally considered high-risk, closer to gambling than systematic trading.
The right number within that range should also reflect your actual edge — a strategy with strong, proven expectancy can reasonably justify sizing at the higher end of the range; an unproven or newly tweaked strategy should size conservatively until it has a track record.
Common mistakes traders make with position sizing
- Sizing by "gut feel" or a round number of lots instead of calculating quantity from the stop-loss distance and a fixed account-risk percentage.
- Increasing position size after a losing streak in an attempt to "win it back" faster — this is exactly when disciplined sizing matters most.
- Not recalculating position size as account equity grows or shrinks, so the actual risk percentage silently drifts away from the intended plan.
- Applying the same risk percentage to every setup regardless of confidence or historical edge, instead of sizing down on lower-conviction setups.
TradeMind’s position sizing calculator and journal automatically track your planned versus actual risk percentage on every trade, so sizing drift gets caught early through Guardian mode.