The molecular building blocks of a target molecule are smallest precursors required to build up the structure of the target molecule. To make a collection of building blocks and their prices for synthetic planning, here we defined building blocks to be commercially or naturally available small molecules. The collection of commercially available building blocks came from 'buyable' molecules crawled from ChemSpace, 33 which is an online catalogue of small molecules. For most buyable molecules listed in ChemSpace, more than one price is given from multiple suppliers. We only chose the lowest price available for these molecules.