Proportion

Hi,

I am not talking of traditional orchestra but generally what's the proportion of violins to cello? For instance, if you have 10 violins, would 5 cellos or double basses be right? Or 20 violins playing the melody, then 10 cellos would be just the right number to provide bass? I am assuming the bass instruments must be fewer than the instruments providing the main melody, but is there a strict ratio?

Thanks,
El