diff --git a/templates/_helpers.tpl b/templates/_helpers.tpl
index 425bd89..b85b350 100644
--- a/templates/_helpers.tpl
+++ b/templates/_helpers.tpl
@@ -30,6 +30,26 @@ shouldn't blow up the rendered chart).
 {{- toYaml (index $cfg .role) -}}
 {{- end -}}
 
+{{/*
+Storage size for a given layer (`filestore` | `database`). Resolution
+order, most-specific first:
+  1. instance.{layer}Storage in the tenant overlay (operator override)
+  2. sizes[size].storage.{layer} (per-tier default)
+  3. legacy chart-level fallback (.Values.odoo.filestoreSize / .Values.postgres.storage)
+This lets operators decouple storage from CPU/RAM tiers — a Small
+instance with lots of attachments can have 50 GB filestore without
+upgrading to Medium for capacity it doesn't need.
+*/}}
+{{- define "instance.storage" -}}
+{{- $size := .Values.instance.size | default "small" -}}
+{{- $tier := index .Values.sizes $size | default (index .Values.sizes "small") -}}
+{{- if eq .layer "filestore" -}}
+{{-   if .Values.instance.filestoreStorage -}}{{ .Values.instance.filestoreStorage }}{{- else if and $tier.storage $tier.storage.filestore -}}{{ $tier.storage.filestore }}{{- else -}}{{ .Values.odoo.filestoreSize | default "10Gi" }}{{- end -}}
+{{- else if eq .layer "database" -}}
+{{-   if .Values.instance.dbStorage -}}{{ .Values.instance.dbStorage }}{{- else if and $tier.storage $tier.storage.database -}}{{ $tier.storage.database }}{{- else -}}{{ .Values.postgres.storage | default "10Gi" }}{{- end -}}
+{{- end -}}
+{{- end -}}
+
 {{/*
 Postgres password. Looks up the existing Secret on upgrades; uses
 .Values.postgres.password if set; otherwise generates a 32-char