The base formula is pip value = pip size x units traded, expressed in the quote-currency. For most pairs the pip size is 0.0001; for yen pairs it is 0.01. Trading 100,000 units of EUR/USD gives 0.0001 x 100,000 = $10 per pip, and because the quote currency is already dollars, a dollar account needs no conversion.
When the quote currency is not your account-currency, divide or multiply by the relevant rate. See pip-value-cross-pair for the awkward cases.
Example: 50,000 units of USD/JPY with USD/JPY at 151.90. Pip value = 0.01 x 50,000 = JPY 500. Converted at 151.90, that is USD 3.29 per pip, so a 30-pip stop risks about $98.
Related: pip-value-cross-pair, nano-lot