diff --git a/scripts/backup.sh b/scripts/backup.sh
index ef0d630..fa06f7e 100755
--- a/scripts/backup.sh
+++ b/scripts/backup.sh
@@ -106,7 +106,14 @@ if [ -z "$AVAILABLE_SPACE" ]; then
   exit 1
 fi
 
-log "INFO" "Espace requis (estimé): $(numfmt --to=iec-i --suffix=B "$REQUIRED_SPACE" 2>/dev/null || echo "$REQUIRED_SPACE bytes")"
+# Calculer estimation avec compression (ratio moyen ~90%)
+if [ "$REQUIRED_SPACE" -gt 0 ] 2>/dev/null; then
+  ESTIMATED_COMPRESSED=$((REQUIRED_SPACE / 10))
+  log "INFO" "Espace requis (non compressé + 20%): $(numfmt --to=iec-i --suffix=B "$REQUIRED_SPACE" 2>/dev/null || echo "$REQUIRED_SPACE bytes")"
+  log "INFO" "Espace estimé après compression: $(numfmt --to=iec-i --suffix=B "$ESTIMATED_COMPRESSED" 2>/dev/null || echo "$ESTIMATED_COMPRESSED bytes")"
+else
+  log "INFO" "Espace requis: Impossible à calculer (utilisation du fallback)"
+fi
 log "INFO" "Espace disponible: $(numfmt --to=iec-i --suffix=B "$AVAILABLE_SPACE" 2>/dev/null || echo "$AVAILABLE_SPACE bytes")"
 
 # Comparaison sécurisée avec validation