Do you mean volume, or weight? If you mean volume, this will vary according to the temperature and pressure of the surrounding air. Increase the temperature and the volume of the plume of smoke you exhale will increase. Increase the pressure of the surrounding air and the volume of the smoke you exhale will decrease.
Mastermind obviously means volume hence "what is the volume" and the volume is pretty much constant, temperature and pressure effect the volume of gases, smoke is not a gas. I am unable to give an answer to the volume though. Also, just out of interest why do you want to find this out, mastermind ?