how can i find the volume of a cube containing 1000 nanoparticle (particle particle interactions are ignored)

we have nano-particles npx=10,npy=10,npz=10 nano-particles in x,y and z direction.so,np=1000 we need to find volume by using the above data. i did as diameter_np(1:np)=(1e-9)*(3+2*randn(1,np)); %3 nm is diameter of Co np radius_np(1:np)=diameter_np(1:np)./2; volume_nps(1:np)=(4/3)*pi*(radius_np(1:np)).^3; %for sample volume of a cube which contain 1000 nanoparticles mean_np=mean(diameter_np(1:np)); side_cube=mean_np*(npx); sample_vol=side_cube*side_cube*side_cube; sample_vol_comp=pac_f*sample_vol;%pac_f is packing fraction kindly send me the correct method thanks in advance

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