Pip value
The money equivalent of one pip for a given trade size; the core input to position sizing and risk calculation.
Pip value = (one pip / exchange rate) × trade size. On pairs where USD is the quote currency (EURUSD, GBPUSD), it's fixed at $10 for a standard lot; on others it varies with the exchange rate.
If you know your stop distance in pips, you find the right lot size by dividing the money risk you accept by the pip value. The Pip Value and Position Sizing calculators in the Tools section do this automatically.