You don't choose a size. You choose how much of the account one trade may lose and where the stop goes, and the desk works out the size and the leverage.
How the size is found
Risk is a percent of your portfolio value. The size is chosen so that the loss at the stop equals that risk, counting the fee to open and the fee to close: the maker fee for a limit entry, the taker fee otherwise, at your account's own rates and including the builder fee.
The risk field's arrows (or the arrow keys) step it by 0.1 below 1% and by 0.25 from 1% up. Stops and targets are typed as a price (81000) or as a distance from the entry (1%).
Example. A $10,000 account risks 1%, so the loss at the stop must be $100. A BTC long at 80,000 with the stop at 79,200 loses $800 per BTC on price, plus 0.07% fees on the way in and out (0.045% taker and 0.025% builder fee), about $111 per BTC. The size is $100 ÷ $911 ≈ 0.11 BTC, a position of about $8,780.
Leverage follows the stop
The desk picks the highest whole leverage, within the market's margin tiers, that keeps the isolated liquidation price at least 1.5 times the stop distance away. A tight stop allows more leverage; a wide one less. The liquidation price is in the summary.
A stop is required
Risk sizing sizes nothing until a stop is typed: the stop field reads "Required" and the button "Set a stop loss to size the trade". The one way to trade without a stop order is Liquidation as stop.
Liquidation as stop
Under Options, Liquidation as stop places no stop order. The position is isolated and its margin equals your risk, so liquidation is the most you can lose.
- With a stop price typed, the leverage puts the liquidation at or just beyond it.
- With the stop left empty, a leverage slider sets how far away the liquidation is. You can also drag the liquidation line on the chart.
- It needs a fresh isolated position, so it is not available while you hold a position in that market.
Manual sizing
Size by margin and leverage (under Options) replaces the risk field: enter a margin and a leverage, or let a target liquidation price set the leverage. The stop is then optional and can be a price, a percent move or a percent of the margin.
Daily loss limit
Off by default; turn it on in Settings as a percent of your equity at the start of the day. Once today's closed trades are down by that much, the account panel shows "Loss limit hit" and the ticket refuses new entries until local midnight, or until later wins bring the day back within the limit.
Closing positions, moving stops and cancelling orders are never blocked.
Open risk
The account panel's Open risk row is what you would lose if every confirmed stop were hit from the current prices, as an amount and a share of equity. It adds "+ unknown" when some position has no confirmed stop. The Risk tab in the bottom panel breaks it down per market, with long, short, gross and net exposure.
Open risk is an estimate. Stops are market orders and can fill worse in a fast or gapping market, and funding is not included.