It depends on what value you want to get - the total number of particles is consant - if you want to get the total number of live particles you could go through the particle array and count up how many particles that have life >= 0. Or you could just as easily count up how many particle have life < 0 and subtract form the total particles, which would be faster. The thing you have to realize though that is every particle is always drawn - as soon as you check for life < 0 you reset the particle and thus redraw it(hope that makes sence). The only thing is that these newly recreated particles dont move.