Most traders decide how big a position should be by feel. A disciplined trader works it out from two numbers: how much of the account they are willing to lose if the idea is wrong, and how far away the stop is.
The formula
Position size = amount at risk ÷ stop distance.
If the account is 1,000 USDT and you risk 1%, the amount at risk is 10 USDT. If the stop is 5% below the entry, the position notional is 10 ÷ 0.05 = 200 USDT. A fill at the planned stop implies about 10 USDT lost before fees and funding; slippage, gaps or liquidation can increase the loss.
Why it works
The stop goes where the idea is clearly wrong, and the size follows from it. A wide stop means a smaller position; a tight stop allows a larger one. The loss when you are wrong stays roughly the same either way.
Try it with the position size calculator in the Pride Academy. It does not place trades and nothing you type leaves your browser.