Standard temperature is equal to 0 °C, which is 273.15 K.
Standard Pressure is 1 Atm, 101.3kPa or 760 mmHg or torr.
STP is the "standard" conditions often used for measuring gas density and volume.
At STP, 1 mole of any gas occupies 22.4L.
Density of a gas at STP= molar mass/22.4L