diff --git a/lib/google_maps_service/apis/roads.rb b/lib/google_maps_service/apis/roads.rb
index 9c2102c..bbc689e 100644
--- a/lib/google_maps_service/apis/roads.rb
+++ b/lib/google_maps_service/apis/roads.rb
@@ -63,8 +63,9 @@ def snap_to_roads(path, interpolate: false)
     #         by the snap_to_roads function. You can pass up to 100 Place IDs.
     #
     # @return [Array] Array of speed limits.
-    def speed_limits(place_ids)
+    def speed_limits(place_ids, units: 'KPH')
       params = GoogleMapsService::Convert.as_list(place_ids).map { |place_id| ['placeId', place_id] }
+      params << ['units', units] if units.match(/^mph$/i)
 
       return get('/v1/speedLimits', params,
                  base_url: ROADS_BASE_URL,
@@ -91,12 +92,13 @@ def speed_limits(place_ids)
     #
     # @return [Hash] A hash with both a list of speed limits and a list of the snapped
     #         points.
-    def snapped_speed_limits(path)
+    def snapped_speed_limits(path, units: 'KPH')
       path = GoogleMapsService::Convert.waypoints(path)
 
       params = {
-        path: path
-      }
+        path: path,
+        units: (units if units.match(/^mph$/i))
+      }.reject {|k,v| v.nil?}
 
       return get('/v1/speedLimits', params,
                  base_url: ROADS_BASE_URL,