diff --git a/src/addons/storagemanager/pages/course-storage/course-storage.html b/src/addons/storagemanager/pages/course-storage/course-storage.html
index b36d1e85d..57b45f33c 100644
--- a/src/addons/storagemanager/pages/course-storage/course-storage.html
+++ b/src/addons/storagemanager/pages/course-storage/course-storage.html
@@ -25,8 +25,8 @@
                         <p class="item-heading ion-text-wrap">{{ 'addon.storagemanager.totaldownloads' | translate }}</p>
                     </ion-label>
                     <ion-badge color="light" slot="end">
-                        <ng-container *ngIf="sizeLoaded">{{ totalSize | coreBytesToSize }}</ng-container>
-                        <ng-container *ngIf="!sizeLoaded">{{ 'core.calculating' | translate }}</ng-container>
+                        <ng-container *ngIf="!calculatingSize">{{ totalSize | coreBytesToSize }}</ng-container>
+                        <ng-container *ngIf="calculatingSize">{{ 'core.calculating' | translate }}</ng-container>
                     </ion-badge>
                 </ion-item>
                 <ion-button *ngIf="downloadCourseEnabled" (click)="prefetchCourse()" expand="block" fill="outline" class="ion-no-margin"
@@ -35,7 +35,7 @@
                     <ion-spinner *ngIf="prefetchCourseData.loading" slot="start"></ion-spinner>
                     {{ prefetchCourseData.statusTranslatable | translate }}
                 </ion-button>
-                <ion-button *ngIf="sizeLoaded && totalSize > 0" (click)="deleteForCourse()" expand="block" color="danger"
+                <ion-button [disabled]="calculatingSize || totalSize <= 0" (click)="deleteForCourse()" expand="block" color="danger"
                     class="ion-no-margin ion-margin-top">
                     <ion-icon name="fas-trash" slot="start" [attr.aria-label]="'addon.storagemanager.deletedatafrom' | translate:
                         { name: title }">
@@ -55,12 +55,12 @@
                                 </core-format-text>
                             </p>
                             <ion-badge [color]="section.downloadStatus == statusDownloaded ? 'success' : 'light'"
-                                *ngIf="section.sizeLoaded && section.totalSize > 0">
+                                *ngIf="!section.calculatingSize && section.totalSize > 0">
                                 <ion-icon name="fam-cloud-done" *ngIf="section.downloadStatus == statusDownloaded"
                                     [attr.aria-label]="'core.downloaded' | translate">
                                 </ion-icon>{{ section.totalSize | coreBytesToSize }}
                             </ion-badge>
-                            <ion-badge color="light" *ngIf="!section.sizeLoaded">
+                            <ion-badge color="light" *ngIf="section.calculatingSize">
                                 {{ 'core.calculating' | translate }}
                             </ion-badge>
                             <!-- Download progress. -->
@@ -69,7 +69,8 @@
                                 </core-progress-bar>
                             </p>
                         </ion-label>
-                        <div class="storage-buttons" slot="end" *ngIf="(section.sizeLoaded && section.totalSize > 0) || downloadEnabled">
+                        <div class="storage-buttons" slot="end"
+                            *ngIf="(!section.calculatingSize && section.totalSize > 0) || downloadEnabled">
                             <div *ngIf="downloadEnabled" slot="end" class="core-button-spinner">
                                 <core-download-refresh *ngIf="!section.isDownloading && section.downloadStatus != statusDownloaded"
                                     [status]="section.downloadStatus" [enabled]="true" (action)="prefecthSection(section)"
@@ -83,7 +84,7 @@
                                     {{section.count}} / {{section.total}}
                                 </ion-badge>
                             </div>
-                            <ion-button (click)="deleteForSection(section)" *ngIf="section.sizeLoaded && section.totalSize > 0"
+                            <ion-button (click)="deleteForSection(section)" *ngIf="!section.calculatingSize && section.totalSize > 0"
                                 color="danger" fill="clear">
                                 <ion-icon name="fas-trash" slot="icon-only"
                                     [attr.aria-label]="'addon.storagemanager.deletedatafrom' | translate: { name: section.name }">
@@ -95,7 +96,7 @@
                 <ion-card-content>
                     <ng-container *ngFor="let module of section.modules">
                         <ion-item class="ion-no-padding core-course-storage-activity"
-                            *ngIf="downloadEnabled || (module.sizeLoaded && module.totalSize > 0)">
+                            *ngIf="downloadEnabled || (!module.calculatingSize && module.totalSize > 0)">
                             <core-mod-icon slot="start" *ngIf="module.handlerData.icon" [modicon]="module.handlerData.icon"
                                 [modname]="module.modname" [componentId]="module.instance">
                             </core-mod-icon>
@@ -106,12 +107,12 @@
                                     </core-format-text>
                                 </h3>
                                 <ion-badge [color]="module.downloadStatus == statusDownloaded ? 'success' : 'light'"
-                                    *ngIf="module.sizeLoaded && module.totalSize > 0">
+                                    *ngIf="!module.calculatingSize && module.totalSize > 0">
                                     <ion-icon name="fam-cloud-done" *ngIf="module.downloadStatus == statusDownloaded"
                                         [attr.aria-label]="'core.downloaded' | translate">
                                     </ion-icon>{{ module.totalSize | coreBytesToSize }}
                                 </ion-badge>
-                                <ion-badge color="light" *ngIf="!module.sizeLoaded">
+                                <ion-badge color="light" *ngIf="module.calculatingSize">
                                     {{ 'core.calculating' | translate }}
                                 </ion-badge>
                             </ion-label>
@@ -123,7 +124,7 @@
                                     (action)="prefetchModule(module, section)">
                                 </core-download-refresh>
                                 <ion-button fill="clear" (click)="deleteForModule(module, section)"
-                                    *ngIf="module.sizeLoaded && module.totalSize > 0" color="danger">
+                                    *ngIf="!module.calculatingSize && module.totalSize > 0" color="danger">
                                     <ion-icon name="fas-trash" slot="icon-only"
                                         [attr.aria-label]="'addon.storagemanager.deletedatafrom' | translate: { name: module.name }">
                                     </ion-icon>
diff --git a/src/addons/storagemanager/pages/course-storage/course-storage.ts b/src/addons/storagemanager/pages/course-storage/course-storage.ts
index 5c3f371cb..39c3d42d0 100644
--- a/src/addons/storagemanager/pages/course-storage/course-storage.ts
+++ b/src/addons/storagemanager/pages/course-storage/course-storage.ts
@@ -48,7 +48,7 @@ export class AddonStorageManagerCourseStoragePage implements OnInit, OnDestroy {
     loaded = false;
     sections: AddonStorageManagerCourseSection[] = [];
     totalSize = 0;
-    sizeLoaded = false;
+    calculatingSize = true;
 
     downloadEnabled = false;
     downloadCourseEnabled = false;
@@ -106,12 +106,20 @@ export class AddonStorageManagerCourseStoragePage implements OnInit, OnDestroy {
 
         const sections = await CoreCourse.getSections(this.courseId, false, true);
         this.sections = (await CoreCourseHelper.addHandlerDataForModules(sections, this.courseId)).sections
-            .map((section) => ({ ...section, totalSize: 0 }));
+            .map(section => ({
+                ...section,
+                totalSize: 0,
+                calculatingSize: true,
+                modules: section.modules.map(module => ({
+                    ...module,
+                    calculatingSize: true,
+                })),
+            }));
 
         this.loaded = true;
 
         await Promise.all([
-            this.loadSizes(),
+            this.initSizes(),
             this.initCoursePrefetch(),
             this.initModulePrefetch(),
         ]);
@@ -240,18 +248,9 @@ export class AddonStorageManagerCourseStoragePage implements OnInit, OnDestroy {
     /**
      * Init section, course and modules sizes.
      */
-    protected async loadSizes(): Promise<void> {
-        this.totalSize = 0;
-        this.sizeLoaded = false;
-
+    protected async initSizes(): Promise<void> {
         await Promise.all(this.sections.map(async (section) => {
-            section.totalSize = 0;
-            section.sizeLoaded = false;
-
             await Promise.all(section.modules.map(async (module) => {
-                module.totalSize = 0;
-                module.sizeLoaded = false;
-
                 // Note: This function only gets the size for modules which are downloadable.
                 // For other modules it always returns 0, even if they have downloaded some files.
                 // However there is no 100% reliable way to actually track the files in this case.
@@ -268,13 +267,13 @@ export class AddonStorageManagerCourseStoragePage implements OnInit, OnDestroy {
                     this.totalSize += size;
                 }
 
-                module.sizeLoaded = true;
+                module.calculatingSize = false;
             }));
 
-            section.sizeLoaded = true;
+            section.calculatingSize = false;
         }));
 
-        this.sizeLoaded = true;
+        this.calculatingSize = false;
 
         // Mark course as not downloaded if course size is 0.
         if (this.totalSize == 0) {
@@ -282,6 +281,56 @@ export class AddonStorageManagerCourseStoragePage implements OnInit, OnDestroy {
         }
     }
 
+    /**
+     * Update the sizes of some modules.
+     *
+     * @param modules Modules.
+     * @param section Section the modules belong to.
+     * @return Promise resolved when done.
+     */
+    protected async updateModulesSizes(
+        modules: AddonStorageManagerModule[],
+        section?: AddonStorageManagerCourseSection,
+    ): Promise<void> {
+        this.calculatingSize = true;
+
+        await Promise.all(modules.map(async (module) => {
+            if (module.calculatingSize) {
+                return;
+            }
+
+            module.calculatingSize = true;
+
+            if (!section) {
+                section = this.sections.find((section) => section.modules.some((mod) => mod.id === module.id));
+                if (section) {
+                    section.calculatingSize = true;
+                }
+            }
+
+            try {
+                const size = await CoreCourseModulePrefetchDelegate.getModuleStoredSize(module, this.courseId);
+
+                const diff = (isNaN(size) ? 0 : size) - (module.totalSize ?? 0);
+
+                module.totalSize = Number(size);
+                this.totalSize += diff;
+                if (section) {
+                    section.totalSize += diff;
+                }
+            } catch {
+                // Ignore errors, it shouldn't happen.
+            } finally {
+                module.calculatingSize = false;
+            }
+        }));
+
+        this.calculatingSize = false;
+        if (section) {
+            section.calculatingSize = false;
+        }
+    }
+
     /**
      * The user has requested a delete for the whole course data.
      *
@@ -406,7 +455,7 @@ export class AddonStorageManagerCourseStoragePage implements OnInit, OnDestroy {
         } finally {
             modal.dismiss();
 
-            await this.loadSizes();
+            await this.updateModulesSizes(modules, section);
             CoreCourseHelper.calculateSectionsStatus(this.sections, this.courseId, false, false);
         }
     }
@@ -455,7 +504,7 @@ export class AddonStorageManagerCourseStoragePage implements OnInit, OnDestroy {
                     CoreDomUtils.showErrorModalDefault(error, 'core.course.errordownloadingsection', true);
                 }
             } finally {
-                await this.loadSizes();
+                await this.updateModulesSizes(section.modules, section);
             }
         } catch (error) {
             // User cancelled or there was an error calculating the size.
@@ -501,7 +550,7 @@ export class AddonStorageManagerCourseStoragePage implements OnInit, OnDestroy {
         } finally {
             module.spinner = false;
 
-            await this.loadSizes();
+            await this.updateModulesSizes([module]);
         }
     }
 
@@ -613,13 +662,13 @@ export class AddonStorageManagerCourseStoragePage implements OnInit, OnDestroy {
 
 type AddonStorageManagerCourseSection = Omit<CoreCourseSectionWithStatus, 'modules'> & {
     totalSize: number;
-    sizeLoaded?: boolean;
+    calculatingSize: boolean;
     modules: AddonStorageManagerModule[];
 };
 
 type AddonStorageManagerModule = CoreCourseModuleData & {
     totalSize?: number;
-    sizeLoaded?: boolean;
+    calculatingSize: boolean;
     prefetchHandler?: CoreCourseModulePrefetchHandler;
     spinner?: boolean;
     downloadStatus?: string;