Phase　change　material　(PCM)　has　been　widely　integrated　in　building　envelops　to　increase　their　thermal　inertia　performance.　To　evaluate　the　thermal　inertia　performance　of　materials　and　envelops,　Chinese　Thermal　Design　Code　has　provided　three　indicators,　namely,　thermal　storage　coefficient,　thermal　resistance　and　thermal　inertia　index.　The　existing　simplified　method　calculating　the　thermal　storage　coefficient　is　only　applicable　for　materials　with　constant　thermal　properties.　For　those　with　varying　thermal　properties,　such　as　PCM,　however,　further　developments　are　still　required.　To　solve　this　issue,　both　dimensional　analysis　and　numerical　simulation　were　carried　out　to　develop　relationships　between　the　thermal　storage　coefficient　of　PCM　and　its　other　thermal　properties　(e.g.　thermal　conductivity,　density　and　the　effective　equivalent　specific　heat).　Based　on　the　developed　relationships,　a　simplified　method　calculating　the　thermal　storage　coefficient　of　PCM　was　proposed　in　this　study.　This　simplified　method　was　then　combined　into　the　thermal　inertia　index　for　evaluating　the　thermal　inertia　performance　of　building　envelops　with　PCM.　(C)　2016　Elsevier　B.V.　All　rights　reserved.