A　full-scale　quantitative　diagnostic　method　is　proposed　in　this　study　for　inner-race　fault-size　estimation　of　ball　bearings.　The　fault　size　is　generally　estimated　using　time　interval　between　double　impacts　if　the　fault　size　is　smaller　than　ball　angular　spacing.　This　method　may　be　inapplicable　when　fault　sizes　become　larger　than　integral　multiples　of　ball　angular　spacing,　which　means　they　have　the　same　time　intervals.　The　analysis　of　dynamic　modelling　reveals　the　existence　of　a　zone　where　load　distribution　is　unaffected　by　the　inner-race　fault　and　the　range　of　the　zone　varies　monotonously　with　the　fault　size.　The　monotonic　relationship　between　the　proportion　of　fault-free　components　in　axis-orbit　time　history　and　fault　size　can　be　explored　using　this　mechanism.　Hence,　a　novel　evaluation　indicator　called　the　axis-orbit　deterioration　degree　(AODD)　is　proposed　in　this　study.　The　expression　of　this　indicator　is　derived　from　theoretical　analysis　and　signal　processing　methods.　AODD　in　the　simulation　and　experimental　studies　can　be　used　to　distinguish　between　faults　that　differ　in　size　by　integral　multiples　of　the　ball　angular　spacing.　A　new　idea　is　proposed　for　the　quantitative　diagnosis　method　of　ball　bearings　to　improve　the　accuracy　of　fault　size　estimation.　(C)　2020　Elsevier　Ltd.　All　rights　reserved.