Forex position sizer
Arithmetic, not advice. It sizes a position from numbers you type — it has no market data, no view on any instrument, and no idea whether your stop is sensible. Nothing you enter leaves your browser. Check the pip size and the conversion rate before you trust the size — a JPY pair uses 0.01, and getting that one field wrong sizes the position a hundred times off.
Two fields decide everything
Pip size. 0.0001 for most pairs, 0.01 for anything quoted in yen. Getting this one wrong sizes the position a hundred times off, in the direction that empties an account.
Quote → account rate. Pip value lands in the pair's second currency, and this converts it to yours. It's 1 when they're the same — EUR/USD on a dollar account. It isn't 1 for USD/JPY on a dollar account, and it isn't 1 for anything on a euro account.
The size is rounded down to the 0.01 lot a broker will accept, never up, so the risk you actually take always lands at or under the risk you chose. Both numbers are shown, because the gap between them is the thing people assume away.