Convert-Me.Com - online units conversion

hi,

im having difficulty understanding the conversion from ppbv to ug/m3.

I know the answer is

(µg/ m3 * 24.45) /molecular weight of compound = ppbv

but when i use the ideal gas law PV=nRT, and i calculate for g/V, i get the units to equal g/L, and then to get ug/m3 i multiply my answer by
1 000 000 000. But the answer i get before i multiply by 1billion is the correct answer. Can someone please tell me why im not supposed to multiply my answer by 1billion?

thanks!!

Hello, this value means the constant of gases, you do not need to transform your units.