\begin{tabular}{@{}lrrr@{}}
\toprule
\multicolumn{2}{c}{\thead{Ingredient}}      & \thead{Percentage} & \thead{Calculation} \\ \midrule
flour             & 1000g &100\%  & 1000g of 1000g = 100\% \\ 
water             & 600g  & 60\%  &  600g of 1000g =  60\% \\ 
sourdough starter & 100g  & 10\%  &  100g of 1000g =  10\% \\ 
salt              &  20g  &  2\%  &   20g of 1000g =   2\% \\ \bottomrule
\end{tabular}