The flow will be variable, depending on the pressure in the bottle, in the beguining being higher and later slower, as pressure in the bottle drops; or if venturi principle is used for that bottle, it will depend on the air flow by the opening of the bottle. Weigh the bottle with the perfume (obtain g1), press the knob and let it spray for some precisely measured time (obtain t), and weigh the bottle again (obtain g2) to find the volume used (g1 minus g2). Divide it by the time in seconds (t), the result will be mils per second.

see also

http://www.ilasseurope.org/ICLASS/iclass2003/plenaries/pl04.pdf

Indeed, Harry is the right person to ask. I briefly looked at the publication he suggested and was not able to find the answer. I am sorry, I did not take the question to be really serious. How precisely you want your measurements to be and what exactly you want to measure? It is very hard to precisely measure jet flow and for your special case spray flow. As I suggested, measuring the consumption of the liquid may give “some” measure, if this is what you want, but I probably wrongly assumed that you wanted to know what is flow of the liquid. Indeed, you may want to measure the gas flow too. Depending on the construction of the nozzle, more or less gas will almost always flow with the liquid. Either as a result of gas entrainment or because the venture effect is used to produce spray. The gas flow before the nozzle you can measure with various flowmeters before the gas would come to the nozzle to create aerosol, and add it to the liquid flow extrapolated from the consumption of the liquid. But they have their limits in precision also. The aerosol flow (liquid and gas together) probably cannot be measured directly because of the extreme turbulences. However, the total flow you may measure if you would blow your aerosol in a balloon put in a pletismograf, and then extrapolate from the volume (integrate), taking into account gas compression and temperature change. This will give quite good results.