diff --git a/lighthouse-core/audits/content-width.js b/lighthouse-core/audits/content-width.js
new file mode 100644
index 000000000000..196bf936f6b6
--- /dev/null
+++ b/lighthouse-core/audits/content-width.js
@@ -0,0 +1,68 @@
+/**
+ * @license
+ * Copyright 2016 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+'use strict';
+
+const Audit = require('./audit');
+
+class ContentWidth extends Audit {
+  /**
+   * @return {!AuditMeta}
+   */
+  static get meta() {
+    return {
+      category: 'Mobile Friendly',
+      name: 'content-width',
+      description: 'Content is sized correctly for the viewport',
+      requiredArtifacts: ['ContentWidth']
+    };
+  }
+
+  /**
+   * @param {!Artifacts} artifacts
+   * @return {!AuditResult}
+   */
+  static audit(artifacts) {
+    if (typeof artifacts.ContentWidth === 'undefined' ||
+        typeof artifacts.ContentWidth.scrollWidth === 'undefined' ||
+        typeof artifacts.ContentWidth.viewportWidth === 'undefined') {
+      return ContentWidth.generateAuditResult({
+        rawValue: false,
+        debugString: 'Unable to find scroll and viewport widths.'
+      });
+    }
+
+    const widthsMatch =
+        artifacts.ContentWidth.scrollWidth === artifacts.ContentWidth.viewportWidth;
+
+    return ContentWidth.generateAuditResult({
+      rawValue: widthsMatch,
+      debugString: this.createDebugString(widthsMatch, artifacts.ContentWidth)
+    });
+  }
+
+  static createDebugString(match, artifact) {
+    if (match) {
+      return '';
+    }
+
+    return 'The content scroll size is ' + artifact.scrollWidth + 'px, ' +
+        'whereas the viewport size is ' + artifact.viewportWidth + 'px.';
+  }
+}
+
+module.exports = ContentWidth;
diff --git a/lighthouse-core/closure/typedefs/Artifacts.js b/lighthouse-core/closure/typedefs/Artifacts.js
index 779129d0fedf..17a7ed17d324 100644
--- a/lighthouse-core/closure/typedefs/Artifacts.js
+++ b/lighthouse-core/closure/typedefs/Artifacts.js
@@ -73,3 +73,6 @@ Artifacts.prototype.CriticalRequestChains;
 
 /** @type {{first: number, complete: number, duration: number, frames: !Array<!Object>, debugString: (string|undefined)}} */
 Artifacts.prototype.Speedline;
+
+/** @type {{scrollWidth: number, viewportWidth: number}} */
+Artifacts.prototype.ContentWidth;
diff --git a/lighthouse-core/config/default.json b/lighthouse-core/config/default.json
index 00230e360aca..3ff3056361ac 100644
--- a/lighthouse-core/config/default.json
+++ b/lighthouse-core/config/default.json
@@ -14,7 +14,8 @@
       "accessibility",
       "screenshots",
       "critical-request-chains",
-      "speedline"
+      "speedline",
+      "content-width"
     ]
   },
   {
@@ -61,7 +62,8 @@
     "color-contrast",
     "image-alt",
     "label",
-    "tabindex"
+    "tabindex",
+    "content-width"
   ],
 
   "aggregations": [{
@@ -225,6 +227,10 @@
         "viewport": {
           "rawValue": true,
           "weight": 1
+        },
+        "content-width": {
+          "value": true,
+          "weight": 1
         }
       }
     }]
diff --git a/lighthouse-core/driver/gatherers/content-width.js b/lighthouse-core/driver/gatherers/content-width.js
new file mode 100644
index 000000000000..8fae8d395f21
--- /dev/null
+++ b/lighthouse-core/driver/gatherers/content-width.js
@@ -0,0 +1,52 @@
+/**
+ * @license
+ * Copyright 2016 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+'use strict';
+
+const Gather = require('./gather');
+
+/* global window, __returnResults */
+
+/* istanbul ignore next */
+function getContentWidth() {
+  // window.innerWidth to get the scrollable size of the window (irrespective of zoom)
+  // window.outerWidth to get the size of the visible area
+  __returnResults({
+    scrollWidth: window.innerWidth,
+    viewportWidth: window.outerWidth
+  });
+}
+
+class ContentWidth extends Gather {
+
+  afterPass(options) {
+    const driver = options.driver;
+
+    return driver.evaluateAsync(`(${getContentWidth.toString()}())`)
+
+    .then(returnedValue => {
+      this.artifact = returnedValue;
+    }, _ => {
+      this.artifact = {
+        scrollWidth: -1,
+        viewportWidth: -1
+      };
+      return;
+    });
+  }
+}
+
+module.exports = ContentWidth;
diff --git a/lighthouse-core/test/audits/content-width.js b/lighthouse-core/test/audits/content-width.js
new file mode 100644
index 000000000000..c82b8f494dc9
--- /dev/null
+++ b/lighthouse-core/test/audits/content-width.js
@@ -0,0 +1,43 @@
+/**
+ * Copyright 2016 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+const Audit = require('../../audits/content-width.js');
+const assert = require('assert');
+
+/* global describe, it*/
+
+describe('Mobile-friendly: content-width audit', () => {
+  it('fails when no input present', () => {
+    return assert.equal(Audit.audit({}).rawValue, false);
+  });
+
+  it('fails when scroll width differs from viewport width', () => {
+    return assert.equal(Audit.audit({
+      ContentWidth: {
+        scrollWidth: 100,
+        viewportWidth: 300
+      }
+    }).rawValue, false);
+  });
+
+  it('passes when widths match', () => {
+    return assert.equal(Audit.audit({
+      ContentWidth: {
+        scrollWidth: 300,
+        viewportWidth: 300
+      }
+    }).rawValue, true);
+  });
+});
diff --git a/lighthouse-core/test/driver/gatherers/content-width.js b/lighthouse-core/test/driver/gatherers/content-width.js
new file mode 100644
index 000000000000..8afa398adfab
--- /dev/null
+++ b/lighthouse-core/test/driver/gatherers/content-width.js
@@ -0,0 +1,59 @@
+/**
+ * Copyright 2016 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+'use strict';
+
+/* eslint-env mocha */
+
+const ContentWidthGatherer = require('../../../driver/gatherers/content-width');
+const assert = require('assert');
+let contentWidthGatherer;
+
+describe('Viewport gatherer', () => {
+  // Reset the Gatherer before each test.
+  beforeEach(() => {
+    contentWidthGatherer = new ContentWidthGatherer();
+  });
+
+  it('returns an artifact', () => {
+    return contentWidthGatherer.afterPass({
+      driver: {
+        evaluateAsync() {
+          return Promise.resolve({
+            scrollWidth: 400,
+            viewportWidth: 400
+          });
+        }
+      }
+    }).then(_ => {
+      assert.ok(typeof contentWidthGatherer.artifact === 'object');
+      assert.ok(contentWidthGatherer.artifact.viewportWidth === 400);
+    });
+  });
+
+  it('handles driver failure', () => {
+    return contentWidthGatherer.afterPass({
+      driver: {
+        evaluateAsync() {
+          return Promise.reject('such a fail');
+        }
+      }
+    }).then(_ => {
+      assert(false);
+    }).catch(_ => {
+      assert.equal(contentWidthGatherer.artifact.scrollWidth, -1);
+    });
+  });
+});