diff --git a/src/ImageUtils.js b/src/ImageUtils.js
new file mode 100644
index 0000000000..a53f4fe31c
--- /dev/null
+++ b/src/ImageUtils.js
@@ -0,0 +1,42 @@
+/*
+Copyright 2015, 2016 OpenMarket Ltd
+
+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';
+
+module.exports = {
+    thumbHeight: function(fullWidth, fullHeight, thumbWidth, thumbHeight) {
+        if (!fullWidth || !fullHeight) {
+            // Cannot calculate thumbnail height for image: missing w/h in metadata. We can't even
+            // log this because it's spammy
+            return undefined;
+        }
+        if (fullWidth < thumbWidth && fullHeight < thumbHeight) {
+            // no scaling needs to be applied
+            return fullHeight;
+        }
+        var widthMulti = thumbWidth / fullWidth;
+        var heightMulti = thumbHeight / fullHeight;
+        if (widthMulti < heightMulti) {
+            // width is the dominant dimension so scaling will be fixed on that
+            return Math.floor(widthMulti * fullHeight);
+        }
+        else {
+            // height is the dominant dimension so scaling will be fixed on that
+            return Math.floor(heightMulti * fullHeight);
+        }
+    },
+}
+