Margin

Required margin depends on the position's size and the leverage for that instrument: at 1:100, a $100,000 position needs $1,000. Free margin is what remains of equity after required margin. Margin level, which is equity divided by used margin as a percentage, shows how close the account is to a margin call or a stop out, when the platform starts closing trades.

On prop accounts, loss limits are usually reached long before margin runs out, so margin is rarely the first constraint. It still matters for traders who hold several positions at once, because a new trade can be rejected for lack of free margin. Firms set leverage, and so margin, by instrument, and should show it in their rules.