Dynamic position sizing is a risk management approach that scales the size of a trade inversely with current market volatility, using a measure such as Average True Range, so that the dollar amount at risk stays roughly constant no matter how calm or turbulent the market is at the time.
Why a fixed contract size is misleading
Trading the same 1.0 BTC size during a quiet consolidation, when the daily average true range might be around $500, exposes a completely different amount of dollar risk than trading that same 1.0 BTC during a sharp volatility expansion, when ATR might triple or quadruple. A trader who never adjusts position size for this is effectively taking on wildly inconsistent risk from one trade to the next, even while believing they are following a consistent rule.
The mechanics of the adjustment
The position size formula divides the dollar amount a trader is willing to risk by the stop distance in price, where the stop distance itself is typically calculated as a multiple of ATR, commonly two times ATR. As ATR rises, the resulting stop distance widens, and because the formula holds dollar risk fixed, the position size shrinks to compensate. As ATR falls, the reverse happens: a tighter stop distance allows for a larger position while still risking the same dollar amount.
Seeing the numbers side by side
Consider a $50,000 account risking 1%, or $500, per trade. In a low volatility regime with ATR at $400, a stop set at two times ATR gives a distance of $800, producing a position size of roughly 0.625 BTC. In a high volatility regime with ATR at $1,200, the same two-times-ATR stop gives a distance of $2,400, producing a much smaller position of roughly 0.208 BTC. If the stop is hit in either scenario, the loss comes out to the same $500, even though the position sizes and price distances involved are entirely different.
What this buys a trader over time
The real benefit shows up over a long series of trades rather than any single one: because every loss costs roughly the same fraction of the account regardless of which volatility regime it occurred in, the equity curve avoids the lopsided damage that comes from taking full-sized positions right as volatility happens to spike. It also removes a subjective decision, how large to trade today, and replaces it with a rule that adjusts automatically as market conditions change.