Star-formation efficiency per free-fall time (${ϵ}_{\mathrm{ff}}$)

The star-formation efficiency per free-fall time is the fraction of gas converted into stars during one gravitational free-fall time, ${ϵ}_{\mathrm{ff}}=t_{\mathrm{ff}}/t_{\mathrm{dep}}$. Molecular clouds commonly have values of order one per cent.