diff --git a/www/Utils.js b/www/Utils.js
index 3d7e6824..8b87f1bf 100644
--- a/www/Utils.js
+++ b/www/Utils.js
@@ -185,6 +185,15 @@ Ext.define('PBS.Utils', {
 	return Ext.String.format(gettext("in {0}"), duration);
     },
 
+    render_size_usage: function(val, max) {
+	if (max === 0) {
+	    return gettext('N/A');
+	}
+	return (val*100/max).toFixed(2) + '% (' +
+	    Ext.String.format(gettext('{0} of {1}'),
+	    Proxmox.Utils.format_size(val), Proxmox.Utils.format_size(max)) + ')';
+    },
+
     constructor: function() {
 	var me = this;
 
diff --git a/www/datastore/Summary.js b/www/datastore/Summary.js
index 4a89460c..ac3f19e2 100644
--- a/www/datastore/Summary.js
+++ b/www/datastore/Summary.js
@@ -51,18 +51,7 @@ Ext.define('PBS.DataStoreInfo', {
 	    let total = store.getById('total').data.value;
 	    let used = store.getById('used').data.value;
 
-	    let percent = 100*used/total;
-	    if (total === 0) {
-		percent = 0;
-	    }
-	    let used_percent = `${percent.toFixed(2)}%`;
-
-	    let usage = used_percent + ' (' +
-		Ext.String.format(
-		    gettext('{0} of {1}'),
-		    Proxmox.Utils.format_size(used),
-		    Proxmox.Utils.format_size(total),
-		) + ')';
+	    let usage = PBS.Utils.render_size_usage(used, total);
 	    vm.set('usagetext', usage);
 	    vm.set('usage', used/total);