Surface　roughness　strongly　affects　the　surface　load-carrying　capacity,　transmission　efficiency,　and　bending　strength　of　gears.　However,　tooth-surface　roughness　is　traditionally　measured　in　terms　of　the　average　roughness　parameter　of　the　tooth　surface,　which　is　satisfactory　for　processing　quality　control　but　inadequate　for　performance　analysis　purposes.　Each　point　of　the　tooth-profile　meshes　sequentially　and　its　parameters　(such　as　slip–roll　ratio,　load,　and　friction)　temporally　vary　throughout　the　gear　transmission　process.　Considering　these　variations,　this　paper　proposes　a　local　roughness　and　evaluation　method　for　analyzing　tooth-profile　wear.　First,　the　gear-tooth　profile　(roughness,　waviness,　and　shape　deviation)　is　obtained　on　multiple　geometric　scales　using　a　roughness　profilometer.　Second,　the　acquired　curves　are　mapped　to　the　gear　coordinate　system　using　the　orthogonal　distance　fitting　algorithm.　Thereafter,　the　contact　of　the　tooth　surface　is　analyzed　under　the　working　conditions　of　a　gear　pair.　The　Hertzian　contact　width　of　the　working　points　of　the　tooth　profile　is　calculated　from　the　root　to　the　top　of　the　tooth,　and　the　roughness　parameter　at　each　point　is　calculated　in　the　contact　area.　The　obtained　roughness　parameters　are　sequentially　connected　to　obtain　the　local　roughness　curve.　Finally,　the　tooth　profile　wear　is　determined　from　the　local　roughness　curve　during　an　FZG　gear　test.　The　local　roughness　curves　provide　accurate　evaluations　of　the　lubrication　state　of　the　tooth　surface　and　the　locations　of　pitting　and　micro-pitting　on　the　tooth　surface.　©　2025　Elsevier　Ltd