diff --git a/atom/browser/api/atom_api_session.cc b/atom/browser/api/atom_api_session.cc
index 1b81decd2be..9c885795ae1 100644
--- a/atom/browser/api/atom_api_session.cc
+++ b/atom/browser/api/atom_api_session.cc
@@ -221,17 +221,32 @@ void RunCallbackInUI(const base::Callback<void(T...)>& callback, T... result) {
                            base::BindOnce(callback, result...));
 }
 
+void ResolveOrRejectPromiseInUI(atom::util::Promise promise, int net_error) {
+  if (net_error != net::OK) {
+    std::string err_msg = net::ErrorToString(net_error);
+    util::Promise::RejectPromise(std::move(promise), std::move(err_msg));
+  } else {
+    util::Promise::ResolveEmptyPromise(std::move(promise));
+  }
+}
+
 // Callback of HttpCache::GetBackend.
 void OnGetBackend(disk_cache::Backend** backend_ptr,
                   Session::CacheAction action,
-                  const net::CompletionCallback& callback,
+                  const atom::util::CopyablePromise& promise,
                   int result) {
   if (result != net::OK) {
-    RunCallbackInUI(callback, result);
+    std::string err_msg =
+        "Failed to retrieve cache backend: " + net::ErrorToString(result);
+    util::Promise::RejectPromise(promise.GetPromise(), std::move(err_msg));
   } else if (backend_ptr && *backend_ptr) {
     if (action == Session::CacheAction::CLEAR) {
-      (*backend_ptr)
-          ->DoomAllEntries(base::Bind(&RunCallbackInUI<int>, callback));
+      auto success =
+          (*backend_ptr)
+              ->DoomAllEntries(base::BindOnce(&ResolveOrRejectPromiseInUI,
+                                              promise.GetPromise()));
+      if (success != net::ERR_IO_PENDING)
+        ResolveOrRejectPromiseInUI(promise.GetPromise(), success);
     } else if (action == Session::CacheAction::STATS) {
       base::StringPairs stats;
       (*backend_ptr)->GetStats(&stats);
@@ -239,30 +254,35 @@ void OnGetBackend(disk_cache::Backend** backend_ptr,
         if (stat.first == "Current size") {
           int current_size;
           base::StringToInt(stat.second, &current_size);
-          RunCallbackInUI(callback, current_size);
+          util::Promise::ResolvePromise<int>(promise.GetPromise(),
+                                             current_size);
           break;
         }
       }
     }
-  } else {
-    RunCallbackInUI<int>(callback, net::ERR_FAILED);
   }
 }
 
 void DoCacheActionInIO(
     const scoped_refptr<net::URLRequestContextGetter>& context_getter,
     Session::CacheAction action,
-    const net::CompletionCallback& callback) {
+    atom::util::Promise promise) {
   auto* request_context = context_getter->GetURLRequestContext();
+
   auto* http_cache = request_context->http_transaction_factory()->GetCache();
-  if (!http_cache)
-    RunCallbackInUI<int>(callback, net::ERR_FAILED);
+  if (!http_cache) {
+    std::string err_msg =
+        "Failed to retrieve cache: " + net::ErrorToString(net::ERR_FAILED);
+    util::Promise::RejectPromise(std::move(promise), std::move(err_msg));
+    return;
+  }
 
   // Call GetBackend and make the backend's ptr accessable in OnGetBackend.
   using BackendPtr = disk_cache::Backend*;
   auto** backend_ptr = new BackendPtr(nullptr);
   net::CompletionCallback on_get_backend =
-      base::Bind(&OnGetBackend, base::Owned(backend_ptr), action, callback);
+      base::Bind(&OnGetBackend, base::Owned(backend_ptr), action,
+                 atom::util::CopyablePromise(promise));
   int rv = http_cache->GetBackend(backend_ptr, on_get_backend);
   if (rv != net::ERR_IO_PENDING)
     on_get_backend.Run(net::OK);
@@ -428,12 +448,18 @@ v8::Local<v8::Promise> Session::ResolveProxy(mate::Arguments* args) {
 }
 
 template <Session::CacheAction action>
-void Session::DoCacheAction(const net::CompletionCallback& callback) {
+v8::Local<v8::Promise> Session::DoCacheAction() {
+  v8::Isolate* isolate = v8::Isolate::GetCurrent();
+  util::Promise promise(isolate);
+  v8::Local<v8::Promise> handle = promise.GetHandle();
+
   base::PostTaskWithTraits(
       FROM_HERE, {BrowserThread::IO},
       base::BindOnce(&DoCacheActionInIO,
                      WrapRefCounted(browser_context_->GetRequestContext()),
-                     action, callback));
+                     action, std::move(promise)));
+
+  return handle;
 }
 
 v8::Local<v8::Promise> Session::ClearStorageData(mate::Arguments* args) {
diff --git a/atom/browser/api/atom_api_session.h b/atom/browser/api/atom_api_session.h
index 00a0bf73d83..7debed6c92c 100644
--- a/atom/browser/api/atom_api_session.h
+++ b/atom/browser/api/atom_api_session.h
@@ -11,6 +11,7 @@
 #include "atom/browser/api/trackable_object.h"
 #include "atom/browser/atom_blob_reader.h"
 #include "atom/browser/net/resolve_proxy_helper.h"
+#include "atom/common/promise_util.h"
 #include "base/values.h"
 #include "content/public/browser/download_manager.h"
 #include "native_mate/handle.h"
@@ -64,7 +65,7 @@ class Session : public mate::TrackableObject<Session>,
   // Methods.
   v8::Local<v8::Promise> ResolveProxy(mate::Arguments* args);
   template <CacheAction action>
-  void DoCacheAction(const net::CompletionCallback& callback);
+  v8::Local<v8::Promise> DoCacheAction();
   v8::Local<v8::Promise> ClearStorageData(mate::Arguments* args);
   void FlushStorageData();
   v8::Local<v8::Promise> SetProxy(mate::Arguments* args);
diff --git a/docs/api/promisification.md b/docs/api/promisification.md
index 80d66bae974..8d2a8b0a9b2 100644
--- a/docs/api/promisification.md
+++ b/docs/api/promisification.md
@@ -13,8 +13,6 @@ When a majority of affected functions are migrated, this flag will be enabled by
 - [dialog.showCertificateTrustDialog([browserWindow, ]options, callback)](https://github.com/electron/electron/blob/master/docs/api/dialog.md#showCertificateTrustDialog)
 - [inAppPurchase.purchaseProduct(productID, quantity, callback)](https://github.com/electron/electron/blob/master/docs/api/in-app-purchase.md#purchaseProduct)
 - [inAppPurchase.getProducts(productIDs, callback)](https://github.com/electron/electron/blob/master/docs/api/in-app-purchase.md#getProducts)
-- [ses.getCacheSize(callback)](https://github.com/electron/electron/blob/master/docs/api/session.md#getCacheSize)
-- [ses.clearCache(callback)](https://github.com/electron/electron/blob/master/docs/api/session.md#clearCache)
 - [ses.getBlobData(identifier, callback)](https://github.com/electron/electron/blob/master/docs/api/session.md#getBlobData)
 - [ses.clearAuthCache(options[, callback])](https://github.com/electron/electron/blob/master/docs/api/session.md#clearAuthCache)
 - [contents.executeJavaScript(code[, userGesture, callback])](https://github.com/electron/electron/blob/master/docs/api/web-contents.md#executeJavaScript)
@@ -47,6 +45,8 @@ When a majority of affected functions are migrated, this flag will be enabled by
 - [ses.clearStorageData([options, callback])](https://github.com/electron/electron/blob/master/docs/api/session.md#clearStorageData)
 - [ses.setProxy(config, callback)](https://github.com/electron/electron/blob/master/docs/api/session.md#setProxy)
 - [ses.resolveProxy(url, callback)](https://github.com/electron/electron/blob/master/docs/api/session.md#resolveProxy)
+- [ses.getCacheSize(callback)](https://github.com/electron/electron/blob/master/docs/api/session.md#getCacheSize)
+- [ses.clearCache(callback)](https://github.com/electron/electron/blob/master/docs/api/session.md#clearCache)
 - [shell.openExternal(url[, options, callback])](https://github.com/electron/electron/blob/master/docs/api/shell.md#openExternal)
 - [webviewTag.capturePage([rect, ]callback)](https://github.com/electron/electron/blob/master/docs/api/webview-tag.md#capturePage)
 - [webviewTag.printToPDF(options, callback)](https://github.com/electron/electron/blob/master/docs/api/webview-tag.md#printToPDF)
diff --git a/docs/api/session.md b/docs/api/session.md
index 07160c8bae6..291794f4885 100644
--- a/docs/api/session.md
+++ b/docs/api/session.md
@@ -97,12 +97,28 @@ The following methods are available on instances of `Session`:
 
 * `callback` Function
   * `size` Integer - Cache size used in bytes.
+  * `error` Integer - The error code corresponding to the failure.
 
 Callback is invoked with the session's current cache size.
 
+**[Deprecated Soon](promisification.md)**
+
+#### `ses.getCacheSize()`
+
+Returns `Promise<Integer>` - the session's current cache size, in bytes.
+
 #### `ses.clearCache(callback)`
 
 * `callback` Function - Called when operation is done.
+  * `error` Integer - The error code corresponding to the failure.
+
+Clears the session’s HTTP cache.
+
+**[Deprecated Soon](promisification.md)**
+
+#### `ses.clearCache()`
+
+Returns `Promise<void>` - resolves when the cache clear operation is complete.
 
 Clears the session’s HTTP cache.
 
diff --git a/docs/styleguide.md b/docs/styleguide.md
index 155d83e8a0a..3a291ccaf08 100644
--- a/docs/styleguide.md
+++ b/docs/styleguide.md
@@ -128,7 +128,7 @@ Using the `Session` and `Cookies` classes as an example:
 
 ### Instance Methods
 
-#### `ses.getCacheSize(callback)`
+#### `ses.getCacheSize()`
 
 ### Instance Properties
 
diff --git a/lib/browser/api/session.js b/lib/browser/api/session.js
index fdff883335f..73cafa07c94 100644
--- a/lib/browser/api/session.js
+++ b/lib/browser/api/session.js
@@ -27,6 +27,8 @@ Session.prototype.clearStorageData = deprecate.promisify(Session.prototype.clear
 Session.prototype.clearHostResolverCache = deprecate.promisify(Session.prototype.clearHostResolverCache)
 Session.prototype.resolveProxy = deprecate.promisify(Session.prototype.resolveProxy)
 Session.prototype.setProxy = deprecate.promisify(Session.prototype.setProxy)
+Session.prototype.getCacheSize = deprecate.promisify(Session.prototype.getCacheSize)
+Session.prototype.clearCache = deprecate.promisify(Session.prototype.clearCache)
 
 Cookies.prototype.flushStore = deprecate.promisify(Cookies.prototype.flushStore)
 Cookies.prototype.get = deprecate.promisify(Cookies.prototype.get)