diff --git a/app/pages/project/instances/InstancesPage.tsx b/app/pages/project/instances/InstancesPage.tsx
index 7bdd3c7eb..e737cc97e 100644
--- a/app/pages/project/instances/InstancesPage.tsx
+++ b/app/pages/project/instances/InstancesPage.tsx
@@ -8,7 +8,7 @@
 import { type UseQueryOptions } from '@tanstack/react-query'
 import { createColumnHelper } from '@tanstack/react-table'
 import { filesize } from 'filesize'
-import { useMemo, useRef } from 'react'
+import { useMemo, useRef, useState } from 'react'
 import { useNavigate, type LoaderFunctionArgs } from 'react-router-dom'
 
 import {
@@ -41,6 +41,7 @@ import { toLocaleTimeString } from '~/util/date'
 import { pb } from '~/util/path-builder'
 
 import { useMakeInstanceActions } from './actions'
+import { ResizeInstanceModal } from './instance/InstancePage'
 
 const EmptyState = () => (
   <EmptyMessage
@@ -77,9 +78,15 @@ const POLL_INTERVAL_SLOW = 60 * sec
 
 export function InstancesPage() {
   const { project } = useProjectSelector()
+  const [resizeInstance, setResizeInstance] = useState<Instance | null>(null)
+
   const { makeButtonActions, makeMenuActions } = useMakeInstanceActions(
     { project },
-    { onSuccess: refetchInstances, onDelete: refetchInstances }
+    {
+      onSuccess: refetchInstances,
+      onDelete: refetchInstances,
+      onResizeClick: setResizeInstance,
+    }
   )
 
   const columns = useMemo(
@@ -221,6 +228,13 @@ export function InstancesPage() {
         <CreateLink to={pb.instancesNew({ project })}>New Instance</CreateLink>
       </TableActions>
       {table}
+      {resizeInstance && (
+        <ResizeInstanceModal
+          instance={resizeInstance}
+          onDismiss={() => setResizeInstance(null)}
+          onListView
+        />
+      )}
     </>
   )
 }
diff --git a/app/pages/project/instances/actions.tsx b/app/pages/project/instances/actions.tsx
index b59e09d45..b9eaf3c1f 100644
--- a/app/pages/project/instances/actions.tsx
+++ b/app/pages/project/instances/actions.tsx
@@ -6,7 +6,6 @@
  * Copyright Oxide Computer Company
  */
 import { useCallback } from 'react'
-import { useNavigate } from 'react-router-dom'
 
 import { instanceCan, useApiMutation, type Instance } from '@oxide/api'
 
@@ -14,7 +13,6 @@ import { HL } from '~/components/HL'
 import { confirmAction } from '~/stores/confirm-action'
 import { confirmDelete } from '~/stores/confirm-delete'
 import { addToast } from '~/stores/toast'
-import { pb } from '~/util/path-builder'
 
 import { fancifyStates } from './instance/tabs/common'
 
@@ -25,13 +23,13 @@ type Options = {
   // hook has to expand to encompass the sum of all the APIs of these hooks it
   // call internally, the abstraction is not good
   onDelete?: () => void
+  onResizeClick?: (instance: Instance) => void
 }
 
 export const useMakeInstanceActions = (
   { project }: { project: string },
   options: Options = {}
 ) => {
-  const navigate = useNavigate()
   // if you also pass onSuccess to mutate(), this one is not overridden — this
   // one runs first, then the one passed to mutate().
   //
@@ -47,6 +45,8 @@ export const useMakeInstanceActions = (
     onSuccess: options.onDelete,
   })
 
+  const { onResizeClick } = options
+
   const makeButtonActions = useCallback(
     (instance: Instance) => {
       const instanceParams = { path: { instance: instance.name }, query: { project } }
@@ -116,7 +116,6 @@ export const useMakeInstanceActions = (
 
   const makeMenuActions = useCallback(
     (instance: Instance) => {
-      const instanceSelector = { project, instance: instance.name }
       const instanceParams = { path: { instance: instance.name }, query: { project } }
       return [
         {
@@ -143,10 +142,11 @@ export const useMakeInstanceActions = (
           ),
         },
         {
-          label: 'View serial console',
-          onActivate() {
-            navigate(pb.serialConsole(instanceSelector))
-          },
+          label: 'Resize',
+          onActivate: () => onResizeClick?.(instance),
+          disabled: !instanceCan.update(instance) && (
+            <>Only {fancifyStates(instanceCan.update.states)} instances can be resized</>
+          ),
         },
         {
           label: 'Delete',
@@ -167,7 +167,10 @@ export const useMakeInstanceActions = (
         },
       ]
     },
-    [project, deleteInstanceAsync, navigate, rebootInstanceAsync]
+    // Do not put `options` in here, refer to the property. options is not ref
+    // stable. Extra renders here cause the row actions menu to close when it
+    // shouldn't, like during polling on instance list.
+    [project, deleteInstanceAsync, rebootInstanceAsync, onResizeClick]
   )
 
   return { makeButtonActions, makeMenuActions }
diff --git a/app/pages/project/instances/instance/InstancePage.tsx b/app/pages/project/instances/instance/InstancePage.tsx
index f9c7fc30c..376635558 100644
--- a/app/pages/project/instances/instance/InstancePage.tsx
+++ b/app/pages/project/instances/instance/InstancePage.tsx
@@ -6,34 +6,52 @@
  * Copyright Oxide Computer Company
  */
 import { filesize } from 'filesize'
-import { useMemo } from 'react'
+import { useMemo, useState } from 'react'
+import { useForm } from 'react-hook-form'
 import { Link, useNavigate, type LoaderFunctionArgs } from 'react-router-dom'
 
 import {
   apiQueryClient,
+  useApiMutation,
   useApiQuery,
   usePrefetchedApiQuery,
+  type Instance,
   type InstanceNetworkInterface,
 } from '@oxide/api'
 import { Instances24Icon } from '@oxide/design-system/icons/react'
 
-import { instanceTransitioning } from '~/api/util'
+import {
+  INSTANCE_MAX_CPU,
+  INSTANCE_MAX_RAM_GiB,
+  instanceCan,
+  instanceTransitioning,
+} from '~/api/util'
 import { ExternalIps } from '~/components/ExternalIps'
+import { NumberField } from '~/components/form/fields/NumberField'
+import { HL } from '~/components/HL'
 import { InstanceDocsPopover } from '~/components/InstanceDocsPopover'
 import { MoreActionsMenu } from '~/components/MoreActionsMenu'
 import { RefreshButton } from '~/components/RefreshButton'
 import { RouteTabs, Tab } from '~/components/RouteTabs'
 import { InstanceStateBadge } from '~/components/StateBadge'
-import { getInstanceSelector, useInstanceSelector } from '~/hooks/use-params'
+import {
+  getInstanceSelector,
+  useInstanceSelector,
+  useProjectSelector,
+} from '~/hooks/use-params'
+import { addToast } from '~/stores/toast'
 import { EmptyCell } from '~/table/cells/EmptyCell'
 import { Button } from '~/ui/lib/Button'
 import { DateTime } from '~/ui/lib/DateTime'
+import { Message } from '~/ui/lib/Message'
+import { Modal } from '~/ui/lib/Modal'
 import { PageHeader, PageTitle } from '~/ui/lib/PageHeader'
 import { PropertiesTable } from '~/ui/lib/PropertiesTable'
 import { Spinner } from '~/ui/lib/Spinner'
 import { Tooltip } from '~/ui/lib/Tooltip'
-import { Truncate } from '~/ui/lib/Truncate'
+import { truncate, Truncate } from '~/ui/lib/Truncate'
 import { pb } from '~/util/path-builder'
+import { GiB } from '~/util/units'
 
 import { useMakeInstanceActions } from '../actions'
 
@@ -91,6 +109,7 @@ const POLL_INTERVAL = 1000
 
 export function InstancePage() {
   const instanceSelector = useInstanceSelector()
+  const [resizeInstance, setResizeInstance] = useState(false)
 
   const navigate = useNavigate()
 
@@ -101,6 +120,7 @@ export function InstancePage() {
       apiQueryClient.invalidateQueries('instanceList')
       navigate(pb.instances(instanceSelector))
     },
+    onResizeClick: () => setResizeInstance(true),
   })
 
   const { data: instance } = usePrefetchedApiQuery(
@@ -233,6 +253,142 @@ export function InstancePage() {
         <Tab to={pb.instanceNetworking(instanceSelector)}>Networking</Tab>
         <Tab to={pb.instanceConnect(instanceSelector)}>Connect</Tab>
       </RouteTabs>
+      {resizeInstance && (
+        <ResizeInstanceModal
+          instance={instance}
+          onDismiss={() => setResizeInstance(false)}
+        />
+      )}
     </>
   )
 }
+
+export function ResizeInstanceModal({
+  instance,
+  onDismiss,
+  onListView = false,
+}: {
+  instance: Instance
+  onDismiss: () => void
+  onListView?: boolean
+}) {
+  const { project } = useProjectSelector()
+  const instanceUpdate = useApiMutation('instanceUpdate', {
+    onSuccess(_updatedInstance) {
+      if (onListView) {
+        apiQueryClient.invalidateQueries('instanceList')
+      } else {
+        apiQueryClient.invalidateQueries('instanceView')
+      }
+      onDismiss()
+      addToast({
+        content: (
+          <>
+            Instance <HL>{instance.name}</HL> resized
+          </>
+        ),
+        cta: onListView
+          ? {
+              text: `View instance`,
+              link: pb.instance({ project, instance: instance.name }),
+            }
+          : undefined, // Only link to the instance if we're not already on that page
+      })
+    },
+    onError: (err) => {
+      addToast({ title: 'Error', content: err.message, variant: 'error' })
+    },
+    onSettled: onDismiss,
+  })
+
+  const form = useForm({
+    defaultValues: {
+      ncpus: instance.ncpus,
+      memory: instance.memory / GiB, // memory is stored as bytes
+    },
+    mode: 'onChange',
+  })
+
+  const canResize = instanceCan.update(instance)
+  const willChange =
+    form.watch('ncpus') !== instance.ncpus || form.watch('memory') !== instance.memory / GiB
+  const isDisabled = !form.formState.isValid || !canResize || !willChange
+
+  const onAction = form.handleSubmit(({ ncpus, memory }) => {
+    instanceUpdate.mutate({
+      path: { instance: instance.name },
+      query: { project },
+      body: { ncpus, memory: memory * GiB, bootDisk: instance.bootDiskId },
+    })
+  })
+
+  return (
+    <Modal title="Resize instance" isOpen onDismiss={onDismiss}>
+      <Modal.Body>
+        <Modal.Section>
+          {!canResize ? (
+            <Message variant="error" content="An instance must be stopped to be resized" />
+          ) : (
+            <Message
+              variant="info"
+              content={
+                <div>
+                  Current (
+                  <span className="text-sans-semi-md">{truncate(instance.name, 20)}</span>
+                  ): {instance.ncpus} vCPUs / {instance.memory / GiB} GiB
+                </div>
+              }
+            />
+          )}
+          <form autoComplete="off" className="space-y-4">
+            <NumberField
+              required
+              label="vCPUs"
+              name="ncpus"
+              min={1}
+              control={form.control}
+              validate={(cpus) => {
+                if (cpus < 1) {
+                  return `Must be at least 1 vCPU`
+                }
+                if (cpus > INSTANCE_MAX_CPU) {
+                  return `CPUs capped to ${INSTANCE_MAX_CPU}`
+                }
+                // We can show this error and therefore inform the user
+                // of the limit rather than preventing it completely
+              }}
+              disabled={!canResize}
+            />
+            <NumberField
+              units="GiB"
+              required
+              label="Memory"
+              name="memory"
+              min={1}
+              control={form.control}
+              validate={(memory) => {
+                if (memory < 1) {
+                  return `Must be at least 1 GiB`
+                }
+                if (memory > INSTANCE_MAX_RAM_GiB) {
+                  return `Can be at most ${INSTANCE_MAX_RAM_GiB} GiB`
+                }
+              }}
+              disabled={!canResize}
+            />
+          </form>
+          {instanceUpdate.error && (
+            <p className="mt-4 text-error">{instanceUpdate.error.message}</p>
+          )}
+        </Modal.Section>
+      </Modal.Body>
+      <Modal.Footer
+        onDismiss={onDismiss}
+        onAction={onAction}
+        actionText="Resize"
+        actionLoading={instanceUpdate.isPending}
+        disabled={isDisabled}
+      />
+    </Modal>
+  )
+}
diff --git a/app/ui/lib/Modal.tsx b/app/ui/lib/Modal.tsx
index d6877b7d7..ab00a1a15 100644
--- a/app/ui/lib/Modal.tsx
+++ b/app/ui/lib/Modal.tsx
@@ -70,8 +70,8 @@ export function Modal({
 
                 <AnimatedDialogContent
                   className={cn(
-                    'pointer-events-auto fixed left-1/2 top-1/2 z-modal m-0 flex max-h-[min(800px,80vh)] w-auto min-w-[24rem] flex-col justify-between rounded-lg border p-0 bg-raise border-secondary elevation-2',
-                    narrow ? 'max-w-[24rem]' : 'max-w-[32rem]'
+                    'pointer-events-auto fixed left-1/2 top-1/2 z-modal m-0 flex max-h-[min(800px,80vh)] w-full flex-col justify-between rounded-lg border p-0 bg-raise border-secondary elevation-2',
+                    narrow ? 'max-w-[24rem]' : 'max-w-[28rem]'
                   )}
                   aria-labelledby={titleId}
                   style={{
@@ -89,7 +89,7 @@ export function Modal({
                   </Dialog.Title>
                   {children}
                   <Dialog.Close
-                    className="absolute right-2 top-3 flex rounded p-2 hover:bg-hover"
+                    className="absolute right-2 top-4 flex items-center justify-center rounded p-2 hover:bg-hover"
                     aria-label="Close"
                   >
                     <Close12Icon className="text-secondary" />
diff --git a/test/e2e/instance.e2e.ts b/test/e2e/instance.e2e.ts
index e011157bb..338e2392f 100644
--- a/test/e2e/instance.e2e.ts
+++ b/test/e2e/instance.e2e.ts
@@ -139,6 +139,72 @@ test('cannot reboot a starting instance, or a stopped instance', async ({ page }
   await expect(page.getByRole('menuitem', { name: 'Reboot' })).toBeDisabled()
 })
 
+test('cannot resize a running or starting instance', async ({ page }) => {
+  await page.goto('/projects/mock-project/instances')
+
+  await expectInstanceState(page, 'db1', 'running')
+  await openRowActions(page, 'db1')
+  await expect(page.getByRole('menuitem', { name: 'Resize' })).toBeDisabled()
+
+  await page.keyboard.press('Escape') // get out of the menu
+
+  await expectInstanceState(page, 'not-there-yet', 'starting')
+  await openRowActions(page, 'not-there-yet')
+  await expect(page.getByRole('menuitem', { name: 'Resize' })).toBeDisabled()
+})
+
+test('can resize a failed or stopped instance', async ({ page }) => {
+  await page.goto('/projects/mock-project/instances')
+  const table = page.getByRole('table')
+
+  // resize 'you-fail', currently in a failed state
+  await expectRowVisible(table, {
+    name: 'you-fail',
+    CPU: '4 vCPU',
+    Memory: '6 GiB',
+    state: expect.stringMatching(/^failed\d+s$/),
+  })
+  await clickRowAction(page, 'you-fail', 'Resize')
+  const resizeModal = page.getByRole('dialog', { name: 'Resize instance' })
+  await expect(resizeModal).toBeVisible()
+  await resizeModal.getByRole('textbox', { name: 'vCPUs' }).fill('10')
+  await resizeModal.getByRole('textbox', { name: 'Memory' }).fill('20')
+  await resizeModal.getByRole('button', { name: 'Resize' }).click()
+  await expectRowVisible(table, {
+    name: 'you-fail',
+    CPU: '10 vCPU',
+    Memory: '20 GiB',
+    state: expect.stringMatching(/^failed\d+s$/),
+  })
+
+  // resize 'db1', which needs to be stopped first
+  await expectRowVisible(table, {
+    name: 'db1',
+    CPU: '2 vCPU',
+    Memory: '4 GiB',
+    state: expect.stringMatching(/^running\d+s$/),
+  })
+
+  await clickRowAction(page, 'db1', 'Stop')
+  await page.getByRole('button', { name: 'Confirm' }).click()
+  await expectInstanceState(page, 'db1', 'stopping')
+  await expectInstanceState(page, 'db1', 'stopped')
+
+  await clickRowAction(page, 'db1', 'Resize')
+  await expect(resizeModal).toBeVisible()
+  await expect(resizeModal.getByText('Current (db1): 2 vCPUs / 4 GiB')).toBeVisible()
+
+  await resizeModal.getByRole('textbox', { name: 'vCPUs' }).fill('8')
+  await resizeModal.getByRole('textbox', { name: 'Memory' }).fill('16')
+  await resizeModal.getByRole('button', { name: 'Resize' }).click()
+  await expectRowVisible(table, {
+    name: 'db1',
+    CPU: '8 vCPU',
+    Memory: '16 GiB',
+    state: expect.stringMatching(/^stopped\d+s$/),
+  })
+})
+
 test('delete from instance detail', async ({ page }) => {
   await page.goto('/projects/mock-project/instances/you-fail')