To convert 20mm of gas to pascals, additional information is required, specifically the density of the gas and the acceleration due to gravity. The formula to use is p = hρg, where p is pressure in pascals (N/m²), h is the height in meters, ρ is the density in kg/m³, and g is the acceleration due to gravity (approximately 9.81 m/s²). Without knowing the gas density, a direct conversion cannot be completed. Understanding these variables is crucial for accurate pressure calculations. Proper application of the formula will yield the pressure in pascals.