diff --git a/www/manager6/Utils.js b/www/manager6/Utils.js
index 8b99371..a9260ec 100644
--- a/www/manager6/Utils.js
+++ b/www/manager6/Utils.js
@@ -1148,6 +1148,16 @@ Ext.define('PVE.Utils', {
             return `${per.toFixed(1)}% of ${maxcpu} ${cpu_label}`;
         },
 
+        // parses a size in the 'disk-size' format of the API, like '32G', into bytes
+        parse_disk_size: function (value) {
+            let match = /^(\d+(?:\.\d+)?)(?:([KMGT])(?:iB)?)?$/.exec(value);
+            if (!match) {
+                return undefined;
+            }
+            let exponent = ['', 'K', 'M', 'G', 'T'].indexOf(match[2] ?? '');
+            return parseFloat(match[1]) * 1024 ** exponent;
+        },
+
         render_bandwidth: function (value) {
             if (!Ext.isNumeric(value)) {
                 return '';
diff --git a/www/manager6/lxc/MPResize.js b/www/manager6/lxc/MPResize.js
index 658123a..ec56adb 100644
--- a/www/manager6/lxc/MPResize.js
+++ b/www/manager6/lxc/MPResize.js
@@ -24,6 +24,17 @@ Ext.define('PVE.window.MPResize', {
         });
     },
 
+    updateNewSize: function () {
+        let me = this;
+        let newSize = '';
+        if (me.currentSize !== undefined && me.hdsizesel.isValid()) {
+            newSize = Proxmox.Utils.format_size(
+                me.currentSize + me.hdsizesel.getValue() * 1024 ** 3,
+            );
+        }
+        me.down('#newSize').setValue(newSize);
+    },
+
     initComponent: function () {
         var me = this;
 
@@ -44,6 +55,11 @@ Ext.define('PVE.window.MPResize', {
                 vtype: 'StorageId',
                 allowBlank: false,
             },
+            {
+                xtype: 'displayfield',
+                itemId: 'currentSize',
+                fieldLabel: gettext('Current Size'),
+            },
         ];
 
         me.hdsizesel = Ext.createWidget('numberfield', {
@@ -54,9 +70,17 @@ Ext.define('PVE.window.MPResize', {
             value: '0',
             fieldLabel: `${gettext('Size Increment')} (${gettext('GiB')})`,
             allowBlank: false,
+            listeners: {
+                change: () => me.updateNewSize(),
+            },
         });
 
         items.push(me.hdsizesel);
+        items.push({
+            xtype: 'displayfield',
+            itemId: 'newSize',
+            fieldLabel: gettext('New Size'),
+        });
 
         me.formPanel = Ext.create('Ext.form.Panel', {
             bodyPadding: 10,
@@ -92,5 +116,22 @@ Ext.define('PVE.window.MPResize', {
         });
 
         me.callParent();
+
+        Proxmox.Utils.API2Request({
+            url: `/nodes/${me.nodename}/lxc/${me.vmid}/config`,
+            method: 'GET',
+            waitMsgTarget: me,
+            failure: (response) => Ext.Msg.alert(gettext('Error'), response.htmlStatus),
+            success: function (response) {
+                let size = PVE.Parser.parseLxcMountPoint(response.result.data[me.disk])?.size;
+                me.currentSize = size ? PVE.Utils.parse_disk_size(size) : undefined;
+                me.down('#currentSize').setValue(
+                    me.currentSize !== undefined
+                        ? Proxmox.Utils.format_size(me.currentSize)
+                        : Proxmox.Utils.unknownText,
+                );
+                me.updateNewSize();
+            },
+        });
     },
 });
diff --git a/www/manager6/qemu/HDResize.js b/www/manager6/qemu/HDResize.js
index 574bfb5..4c2ac58 100644
--- a/www/manager6/qemu/HDResize.js
+++ b/www/manager6/qemu/HDResize.js
@@ -25,6 +25,17 @@ Ext.define('PVE.window.HDResize', {
         });
     },
 
+    updateNewSize: function () {
+        let me = this;
+        let newSize = '';
+        if (me.currentSize !== undefined && me.hdsizesel.isValid()) {
+            newSize = Proxmox.Utils.format_size(
+                me.currentSize + me.hdsizesel.getValue() * 1024 ** 3,
+            );
+        }
+        me.down('#newSize').setValue(newSize);
+    },
+
     initComponent: function () {
         var me = this;
 
@@ -45,6 +56,11 @@ Ext.define('PVE.window.HDResize', {
                 vtype: 'StorageId',
                 allowBlank: false,
             },
+            {
+                xtype: 'displayfield',
+                itemId: 'currentSize',
+                fieldLabel: gettext('Current Size'),
+            },
         ];
 
         me.hdsizesel = Ext.createWidget('numberfield', {
@@ -55,9 +71,17 @@ Ext.define('PVE.window.HDResize', {
             value: '0',
             fieldLabel: `${gettext('Size Increment')} (${gettext('GiB')})`,
             allowBlank: false,
+            listeners: {
+                change: () => me.updateNewSize(),
+            },
         });
 
         items.push(me.hdsizesel);
+        items.push({
+            xtype: 'displayfield',
+            itemId: 'newSize',
+            fieldLabel: gettext('New Size'),
+        });
 
         me.formPanel = Ext.create('Ext.form.Panel', {
             bodyPadding: 10,
@@ -87,7 +111,6 @@ Ext.define('PVE.window.HDResize', {
         Ext.apply(me, {
             modal: true,
             width: 250,
-            height: 150,
             border: false,
             layout: 'fit',
             buttons: [submitBtn],
@@ -95,5 +118,22 @@ Ext.define('PVE.window.HDResize', {
         });
 
         me.callParent();
+
+        Proxmox.Utils.API2Request({
+            url: `/nodes/${me.nodename}/qemu/${me.vmid}/config`,
+            method: 'GET',
+            waitMsgTarget: me,
+            failure: (response) => Ext.Msg.alert(gettext('Error'), response.htmlStatus),
+            success: function (response) {
+                let size = PVE.Parser.parseQemuDrive(me.disk, response.result.data[me.disk])?.size;
+                me.currentSize = size ? PVE.Utils.parse_disk_size(size) : undefined;
+                me.down('#currentSize').setValue(
+                    me.currentSize !== undefined
+                        ? Proxmox.Utils.format_size(me.currentSize)
+                        : Proxmox.Utils.unknownText,
+                );
+                me.updateNewSize();
+            },
+        });
     },
 });