This　paper　presents　a　conceptual　product　design　method　that　considers　the　carbon　emission　factors　of　mechanical　and　electrical　products.　This　method　aims　to　consider　low　carbon　issues　prior　to　product　design.　Based　on　a　comprehensive　analysis　of　conventional　product　design　procedures,　the　study　extracts　design　information　related　to　greenhouse　gas　(GHG)　emissions,　itemizes　and　quantifies　the　information,　and　ultimately　uncovers　the　relationship　among　carbon　emissions,　function,　and　economic　factors　of　newly　designed　products.　This　study　explains　the　proposed　concepts　of　carbon　efficiency　(CE)　and　carbon　factor　and　combines　them　with　the　product　design　process　to　present　a　low-carbon　design　process　of　mechanical　and　electrical　products.　Furthermore,　this　paper　presents　a　low-carbon　design　method　of　mechanical　and　electrical　products,　drawing　on　the　product　family　design　idea,　with　GHG　efficiency　and　cost　constraint.　In　particular,　GHG　efficiency　pays　attention　to　product　function　realization　efficiency　and　economic　factors.　The　potential　value　of　the　method　is　demonstrated　in　a　case　study　of　a　tomato　picking　robot.　©　2023,　The　Author(s),　under　exclusive　licence　to　Springer-Verlag　London　Ltd.,　part　of　Springer　Nature.