The formula for calculating boiler pressure using the ideal gas law is as follows: P = (n * R * T) / V Where: P is the absolute pressure in pascals (Pa). n is the number of moles of gas. R is the specific gas constant for the gas (for steam, R = 461.5 J/(kg·K) or 8.314 J/(mol·K) if using moles). T is the absolute temperature in kelvin (K). V is the volume occupied by the gas.