A worked example

Say your account holds 1000 USDT and you'll risk at most 2% on this trade — that's 20 USDT. The coin you like has an entry of 100 and you put the stop at 92, so the risk per unit is 8. Divide 20 by 8 and you can buy about 2.5 units: a position worth 250 USDT, 25% of your capital. If the stop actually triggers, your loss is locked at around 20 USDT and can't run away from you. Swap in your own numbers and the calculator above works it out live.

Why size it this way

The professional name for this is "fixed-risk position sizing": each trade only risks a small slice of the account (commonly 1%–2%). That way even a run of losing trades doesn't do real damage. The point of it is to put "how much I can lose" — the part you control — ahead of "where the price will go" — the part you don't.

A note for beginnersThis tool won't make you money; it only helps you afford to lose. The people who stay in the game long-term usually aren't the ones who win biggest — they're the ones who never blew up their whole account on a single trade. If you want to understand the difference between spot and futures first, read this one.