diff --git a/src/server/editorServices.ts b/src/server/editorServices.ts
index ac80f43c84c..23baa9119bf 100644
--- a/src/server/editorServices.ts
+++ b/src/server/editorServices.ts
@@ -123,11 +123,22 @@ namespace ts.server {
 
     export interface FileStats {
         readonly js: number;
+        readonly jsSize?: number;
+
         readonly jsx: number;
+        readonly jsxSize?: number;
+
         readonly ts: number;
+        readonly tsSize?: number;
+
         readonly tsx: number;
+        readonly tsxSize?: number;
+
         readonly dts: number;
+        readonly dtsSize?: number;
+
         readonly deferred: number;
+        readonly deferredSize?: number;
     }
 
     export interface OpenFileInfo {
@@ -1600,7 +1611,7 @@ namespace ts.server {
             setProjectOptionsUsed(project);
             const data: ProjectInfoTelemetryEventData = {
                 projectId: this.host.createSHA256Hash(project.projectName),
-                fileStats: countEachFileTypes(project.getScriptInfos()),
+                fileStats: countEachFileTypes(project.getScriptInfos(), /*includeSizes*/ true),
                 compilerOptions: convertCompilerOptionsForTelemetry(project.getCompilationSettings()),
                 typeAcquisition: convertTypeAcquisition(project.getTypeAcquisition()),
                 extends: projectOptions && projectOptions.configHasExtendsProperty,
diff --git a/src/server/project.ts b/src/server/project.ts
index 7b11f48fbd6..45d932abc3e 100644
--- a/src/server/project.ts
+++ b/src/server/project.ts
@@ -10,26 +10,43 @@ namespace ts.server {
     export type Mutable<T> = { -readonly [K in keyof T]: T[K]; };
 
     /* @internal */
-    export function countEachFileTypes(infos: ScriptInfo[]): FileStats {
-        const result: Mutable<FileStats> = { js: 0, jsx: 0, ts: 0, tsx: 0, dts: 0, deferred: 0 };
+    export function countEachFileTypes(infos: ScriptInfo[], includeSizes = false): FileStats {
+        const result: Mutable<FileStats> = {
+            js: 0, jsSize: 0,
+            jsx: 0, jsxSize: 0,
+            ts: 0, tsSize: 0,
+            tsx: 0, tsxSize: 0,
+            dts: 0, dtsSize: 0,
+            deferred: 0, deferredSize: 0,
+        };
         for (const info of infos) {
+            const fileSize = includeSizes ? info.getTelemetryFileSize() : 0;
             switch (info.scriptKind) {
                 case ScriptKind.JS:
                     result.js += 1;
+                    result.jsSize! += fileSize;
                     break;
                 case ScriptKind.JSX:
                     result.jsx += 1;
+                    result.jsxSize! += fileSize;
                     break;
                 case ScriptKind.TS:
-                    fileExtensionIs(info.fileName, Extension.Dts)
-                        ? result.dts += 1
-                        : result.ts += 1;
+                    if (fileExtensionIs(info.fileName, Extension.Dts)) {
+                        result.dts += 1;
+                        result.dtsSize! += fileSize;
+                    }
+                    else {
+                        result.ts += 1;
+                        result.tsSize! += fileSize;
+                    }
                     break;
                 case ScriptKind.TSX:
                     result.tsx += 1;
+                    result.tsxSize! += fileSize;
                     break;
                 case ScriptKind.Deferred:
                     result.deferred += 1;
+                    result.deferredSize! += fileSize;
                     break;
             }
         }
diff --git a/src/server/scriptInfo.ts b/src/server/scriptInfo.ts
index 4e3a67748dd..77329099871 100644
--- a/src/server/scriptInfo.ts
+++ b/src/server/scriptInfo.ts
@@ -25,6 +25,14 @@ namespace ts.server {
          */
         private lineMap: number[] | undefined;
 
+        /**
+         * When a large file is loaded, text will artificially be set to "".
+         * In order to be able to report correct telemetry, we store the actual
+         * file size in this case.  (In other cases where text === "", e.g.
+         * for mixed content or dynamic files, fileSize will be undefined.)
+         */
+        private fileSize: number | undefined;
+
         /**
          * True if the text is for the file thats open in the editor
          */
@@ -56,10 +64,12 @@ namespace ts.server {
             this.switchToScriptVersionCache();
         }
 
+        /** Public for testing */
         public useText(newText?: string) {
             this.svc = undefined;
             this.text = newText;
             this.lineMap = undefined;
+            this.fileSize = undefined;
             this.version.text++;
         }
 
@@ -68,13 +78,14 @@ namespace ts.server {
             this.ownFileText = false;
             this.text = undefined;
             this.lineMap = undefined;
+            this.fileSize = undefined;
         }
 
         /**
          * Set the contents as newText
          * returns true if text changed
          */
-        public reload(newText: string) {
+        public reload(newText: string): boolean {
             Debug.assert(newText !== undefined);
 
             // Reload always has fresh content
@@ -91,6 +102,8 @@ namespace ts.server {
                 this.ownFileText = false;
                 return true;
             }
+
+            return false;
         }
 
         /**
@@ -98,7 +111,9 @@ namespace ts.server {
          * returns true if text changed
          */
         public reloadWithFileText(tempFileName?: string) {
-            const reloaded = this.reload(this.getFileText(tempFileName));
+            const { text: newText, fileSize } = this.getFileTextAndSize(tempFileName);
+            const reloaded = this.reload(newText);
+            this.fileSize = fileSize; // NB: after reload since reload clears it
             this.ownFileText = !tempFileName || tempFileName === this.fileName;
             return reloaded;
         }
@@ -118,6 +133,23 @@ namespace ts.server {
             this.pendingReloadFromDisk = true;
         }
 
+        /**
+         * For telemetry purposes, we would like to be able to report the size of the file.
+         * However, we do not want telemetry to require extra file I/O so we report a size
+         * that may be stale (e.g. may not reflect change made on disk since the last reload).
+         * NB: Will read from disk if the file contents have never been loaded because
+         * telemetry falsely indicating size 0 would be counter-productive.
+         */
+        public getTelemetryFileSize(): number {
+            return !!this.fileSize
+                ? this.fileSize
+                : !!this.text // Check text before svc because its length is cheaper
+                    ? this.text.length // Could be wrong if this.pendingReloadFromDisk
+                    : !!this.svc
+                        ? this.svc.getSnapshot().getLength() // Could be wrong if this.pendingReloadFromDisk
+                        : this.getSnapshot().getLength(); // Should be strictly correct
+        }
+
         public getSnapshot(): IScriptSnapshot {
             return this.useScriptVersionCacheIfValidOrOpen()
                 ? this.svc!.getSnapshot()
@@ -161,7 +193,7 @@ namespace ts.server {
             return this.svc!.positionToLineOffset(position);
         }
 
-        private getFileText(tempFileName?: string) {
+        private getFileTextAndSize(tempFileName?: string): { text: string, fileSize?: number } {
             let text: string;
             const fileName = tempFileName || this.fileName;
             const getText = () => text === undefined ? (text = this.host.readFile(fileName) || "") : text;
@@ -173,10 +205,10 @@ namespace ts.server {
                     const service = this.info.containingProjects[0].projectService;
                     service.logger.info(`Skipped loading contents of large file ${fileName} for info ${this.info.fileName}: fileSize: ${fileSize}`);
                     this.info.containingProjects[0].projectService.sendLargeFileReferencedEvent(fileName, fileSize);
-                    return "";
+                    return { text: "", fileSize };
                 }
             }
-            return getText();
+            return { text: getText() };
         }
 
         private switchToScriptVersionCache(): ScriptVersionCache {
@@ -276,6 +308,11 @@ namespace ts.server {
             return this.textStorage.version;
         }
 
+        /*@internal*/
+        getTelemetryFileSize() {
+            return this.textStorage.getTelemetryFileSize();
+        }
+
         /*@internal*/
         public isDynamicOrHasMixedContent() {
             return this.hasMixedContent || this.isDynamic;
diff --git a/src/testRunner/unittests/telemetry.ts b/src/testRunner/unittests/telemetry.ts
index 1c11a40c2ee..f2a7d854124 100644
--- a/src/testRunner/unittests/telemetry.ts
+++ b/src/testRunner/unittests/telemetry.ts
@@ -211,15 +211,36 @@ namespace ts.projectSystem {
             }, "/jsconfig.json");
         });
 
+        it("sends telemetry for file sizes", () => {
+            const jsFile = makeFile("/a.js", "1");
+            const tsFile = makeFile("/b.ts", "12");
+            const tsconfig = makeFile("/jsconfig.json", {
+                compilerOptions: autoJsCompilerOptions
+            });
+            const et = new TestServerEventManager([tsconfig, jsFile, tsFile]);
+            et.service.openClientFile(jsFile.path);
+            et.assertProjectInfoTelemetryEvent({
+                fileStats: fileStats({ js: 1, jsSize: 1, ts: 1, tsSize: 2 }),
+                compilerOptions: autoJsCompilerOptions,
+                typeAcquisition: {
+                    enable: true,
+                    include: false,
+                    exclude: false,
+                },
+                configFileName: "jsconfig.json",
+            }, "/jsconfig.json");
+        });
+
         it("detects whether language service was disabled", () => {
             const file = makeFile("/a.js");
             const tsconfig = makeFile("/jsconfig.json", {});
             const et = new TestServerEventManager([tsconfig, file]);
-            et.host.getFileSize = () => server.maxProgramSizeForNonTsFiles + 1;
+            const fileSize = server.maxProgramSizeForNonTsFiles + 1;
+            et.host.getFileSize = () => fileSize;
             et.service.openClientFile(file.path);
             et.getEvent<server.ProjectLanguageServiceStateEvent>(server.ProjectLanguageServiceStateEvent);
             et.assertProjectInfoTelemetryEvent({
-                fileStats: fileStats({ js: 1 }),
+                fileStats: fileStats({ js: 1, jsSize: fileSize }),
                 compilerOptions: autoJsCompilerOptions,
                 configFileName: "jsconfig.json",
                 typeAcquisition: {
diff --git a/src/testRunner/unittests/textStorage.ts b/src/testRunner/unittests/textStorage.ts
index 5486cf57745..5dce083120b 100644
--- a/src/testRunner/unittests/textStorage.ts
+++ b/src/testRunner/unittests/textStorage.ts
@@ -29,20 +29,20 @@ namespace ts.textStorage {
                 for (let offset = 0; offset < end - start; offset++) {
                     const pos1 = ts1.lineOffsetToPosition(line + 1, offset + 1);
                     const pos2 = ts2.lineOffsetToPosition(line + 1, offset + 1);
-                    assert.isTrue(pos1 === pos2, `lineOffsetToPosition ${line + 1}-${offset + 1}: expected ${pos1} to equal ${pos2}`);
+                    assert.strictEqual(pos1, pos2, `lineOffsetToPosition ${line + 1}-${offset + 1}: expected ${pos1} to equal ${pos2}`);
                 }
 
                 const {start: start1, length: length1 } = ts1.lineToTextSpan(line);
                 const {start: start2, length: length2 } = ts2.lineToTextSpan(line);
-                assert.isTrue(start1 === start2, `lineToTextSpan ${line}::start:: expected ${start1} to equal ${start2}`);
-                assert.isTrue(length1 === length2, `lineToTextSpan ${line}::length:: expected ${length1} to equal ${length2}`);
+                assert.strictEqual(start1, start2, `lineToTextSpan ${line}::start:: expected ${start1} to equal ${start2}`);
+                assert.strictEqual(length1, length2, `lineToTextSpan ${line}::length:: expected ${length1} to equal ${length2}`);
             }
 
             for (let pos = 0; pos < f.content.length; pos++) {
                 const { line: line1, offset: offset1 } = ts1.positionToLineOffset(pos);
                 const { line: line2, offset: offset2 } = ts2.positionToLineOffset(pos);
-                assert.isTrue(line1 === line2, `positionToLineOffset ${pos}::line:: expected ${line1} to equal ${line2}`);
-                assert.isTrue(offset1 === offset2, `positionToLineOffset ${pos}::offset:: expected ${offset1} to equal ${offset2}`);
+                assert.strictEqual(line1, line2, `positionToLineOffset ${pos}::line:: expected ${line1} to equal ${line2}`);
+                assert.strictEqual(offset1, offset2, `positionToLineOffset ${pos}::offset:: expected ${offset1} to equal ${offset2}`);
             }
         });
 
@@ -52,16 +52,93 @@ namespace ts.textStorage {
             const ts1 = new server.TextStorage(host, server.asNormalizedPath(f.path), /*initialVersion*/ undefined, /*info*/undefined!);
 
             ts1.getSnapshot();
-            assert.isTrue(!ts1.hasScriptVersionCache_TestOnly(), "should not have script version cache - 1");
+            assert.isFalse(ts1.hasScriptVersionCache_TestOnly(), "should not have script version cache - 1");
 
             ts1.edit(0, 5, "   ");
             assert.isTrue(ts1.hasScriptVersionCache_TestOnly(), "have script version cache - 1");
 
             ts1.useText();
-            assert.isTrue(!ts1.hasScriptVersionCache_TestOnly(), "should not have script version cache - 2");
+            assert.isFalse(ts1.hasScriptVersionCache_TestOnly(), "should not have script version cache - 2");
 
             ts1.getLineInfo(0);
             assert.isTrue(ts1.hasScriptVersionCache_TestOnly(), "have script version cache - 2");
         });
+
+        it("should be able to return the file size immediately after construction", () => {
+            const host = projectSystem.createServerHost([f]);
+            // Since script info is not used in these tests, just cheat by passing undefined
+            const ts1 = new server.TextStorage(host, server.asNormalizedPath(f.path), /*initialVersion*/ undefined, /*info*/undefined!);
+
+            assert.strictEqual(f.content.length, ts1.getTelemetryFileSize());
+        });
+
+        it("should be able to return the file size when backed by text", () => {
+            const host = projectSystem.createServerHost([f]);
+            // Since script info is not used in these tests, just cheat by passing undefined
+            const ts1 = new server.TextStorage(host, server.asNormalizedPath(f.path), /*initialVersion*/ undefined, /*info*/undefined!);
+
+            ts1.useText(f.content);
+            assert.isFalse(ts1.hasScriptVersionCache_TestOnly());
+
+            assert.strictEqual(f.content.length, ts1.getTelemetryFileSize());
+        });
+
+        it("should be able to return the file size when backed by a script version cache", () => {
+            const host = projectSystem.createServerHost([f]);
+            // Since script info is not used in these tests, just cheat by passing undefined
+            const ts1 = new server.TextStorage(host, server.asNormalizedPath(f.path), /*initialVersion*/ undefined, /*info*/undefined!);
+
+            ts1.useScriptVersionCache_TestOnly();
+            assert.isTrue(ts1.hasScriptVersionCache_TestOnly());
+
+            assert.strictEqual(f.content.length, ts1.getTelemetryFileSize());
+        });
+
+        it("should be able to return the file size when a JS file is too large to load into text", () => {
+            const largeFile = {
+                path: "/a/large.js",
+                content: " ".repeat(server.maxFileSize + 1)
+            };
+
+            const host = projectSystem.createServerHost([largeFile]);
+
+            // The large-file handling requires a ScriptInfo with a containing project
+            const projectService = projectSystem.createProjectService(host);
+            projectService.openClientFile(largeFile.path);
+            const scriptInfo = projectService.getScriptInfo(largeFile.path);
+
+            const ts1 = new server.TextStorage(host, server.asNormalizedPath(largeFile.path), /*initialVersion*/ undefined, scriptInfo!);
+
+            assert.isTrue(ts1.reloadFromDisk());
+            assert.isFalse(ts1.hasScriptVersionCache_TestOnly());
+
+            assert.strictEqual(largeFile.content.length, ts1.getTelemetryFileSize());
+        });
+
+        it("should return the file size without reloading the file", () => {
+            const oldText = "hello";
+            const newText = "goodbye";
+
+            const changingFile = {
+                path: "/a/changing.ts",
+                content: oldText
+            };
+
+            const host = projectSystem.createServerHost([changingFile]);
+            // Since script info is not used in these tests, just cheat by passing undefined
+            const ts1 = new server.TextStorage(host, server.asNormalizedPath(changingFile.path), /*initialVersion*/ undefined, /*info*/undefined!);
+
+            assert.isTrue(ts1.reloadFromDisk());
+
+            // Refresh the file and notify TextStorage
+            host.writeFile(changingFile.path, newText);
+            ts1.delayReloadFromFileIntoText();
+
+            assert.strictEqual(oldText.length, ts1.getTelemetryFileSize());
+
+            assert.isTrue(ts1.reloadWithFileText());
+
+            assert.strictEqual(newText.length, ts1.getTelemetryFileSize());
+        });
     });
 }
diff --git a/src/testRunner/unittests/tsserverProjectSystem.ts b/src/testRunner/unittests/tsserverProjectSystem.ts
index ef01e2a740c..cda60e9b5ff 100644
--- a/src/testRunner/unittests/tsserverProjectSystem.ts
+++ b/src/testRunner/unittests/tsserverProjectSystem.ts
@@ -183,7 +183,7 @@ namespace ts.projectSystem {
     }
 
     export function fileStats(nonZeroStats: Partial<server.FileStats>): server.FileStats {
-        return { ts: 0, tsx: 0, dts: 0, js: 0, jsx: 0, deferred: 0, ...nonZeroStats };
+        return { ts: 0, tsSize: 0, tsx: 0, tsxSize: 0, dts: 0, dtsSize: 0, js: 0, jsSize: 0, jsx: 0, jsxSize: 0, deferred: 0, deferredSize: 0, ...nonZeroStats };
     }
 
     export interface ConfigFileDiagnostic {
diff --git a/tests/baselines/reference/api/tsserverlibrary.d.ts b/tests/baselines/reference/api/tsserverlibrary.d.ts
index 910f3dce467..c3076883b46 100644
--- a/tests/baselines/reference/api/tsserverlibrary.d.ts
+++ b/tests/baselines/reference/api/tsserverlibrary.d.ts
@@ -8437,11 +8437,17 @@ declare namespace ts.server {
     }
     interface FileStats {
         readonly js: number;
+        readonly jsSize?: number;
         readonly jsx: number;
+        readonly jsxSize?: number;
         readonly ts: number;
+        readonly tsSize?: number;
         readonly tsx: number;
+        readonly tsxSize?: number;
         readonly dts: number;
+        readonly dtsSize?: number;
         readonly deferred: number;
+        readonly deferredSize?: number;
     }
     interface OpenFileInfo {
         readonly checkJs: boolean;