The axial stress equation can be rearranged to give A = P / σ {\displaystyle A=P/\sigma } . Substituting this into the weight equation gives w = ρ ( P / σ ) L = ρ L P / σ {\displaystyle w=\rho (P/\sigma )L=\rho LP/\sigma } . Next, the material variables and design variables are grouped separately, giving w = ( ρ / σ ) L P {\displaystyle w=(\rho /\sigma )LP} .