How the size is worked out

The stop decides the size, not the other way round. First decide how much of the account this one idea may cost. Then put the stop where the idea is proven wrong. The distance between entry and stop is the loss on each unit, so the number of units is the money at risk divided by that distance.

units = money at risk ÷ (|entry − stop| + fees on both sides) money at risk = balance × risk %

Worked example: a $10,000 account risking 1% has $100 at risk. A long at 76,600 with a stop at 74,700 loses 1,900 a coin, plus about 75.65 in fees at 0.05% a side, so the position is about 0.0506 BTC, worth about $3,877. If the stop fills, the loss is $100, fees included.

Leverage does not change your risk

Risk is set by the size and the stop. Leverage only changes how much margin the exchange holds against the position. The trap is the liquidation price: if leverage is high enough, the exchange closes you before your stop is reached, at a worse price. The calculator flags that, using the usual isolated-margin estimate. Your exchange's exact figure depends on its margin tiers and fees.

What percent should I risk per trade?

There is no single right number, but it should be small enough that a long losing run is survivable. At 1% a trade, ten losses in a row costs about 9.6% of the account. At 5% a trade, the same run costs about 40%, which needs a 67% gain to recover. Run your own numbers through the risk of ruin calculator.

Reward to risk

With a target, the calculator gives the reward to risk after fees, the profit if it hits, and the loss if the stop fills. What a given reward to risk needs as a win rate is on the expectancy calculator.