diff --git a/exp_scenario/module/commands/lawnmower.lua b/exp_scenario/module/commands/lawnmower.lua
index f75f2fdc..b74c39cb 100644
--- a/exp_scenario/module/commands/lawnmower.lua
+++ b/exp_scenario/module/commands/lawnmower.lua
@@ -28,8 +28,8 @@ commands.lawnmower = Commands.new("lawnmower", { "exp-commands_lawnmower.descrip
 SelectArea:on_selection(function(event)
     local player = assert(game.get_player(event.player_index))
     local area = AABB.expand(event.area)
+    local area_size = AABB.size(area)
     local surface = event.surface
-    local area_size = (area.right_bottom.x - area.left_top.x) * (area.right_bottom.y - area.left_top.y)
 
     if area_size > 1000 then
         player.print({ "exp-commands_lawnmower.area-too-large", 1000, area_size }, Commands.print_settings.error)
diff --git a/exp_scenario/module/commands/surface.lua b/exp_scenario/module/commands/surface.lua
index 1d98e96a..afe630f7 100644
--- a/exp_scenario/module/commands/surface.lua
+++ b/exp_scenario/module/commands/surface.lua
@@ -75,8 +75,8 @@ commands.clear_blueprints = Commands.new("clear-blueprints", { "exp-commands_sur
 SelectArea:on_selection(function(event)
     local player = assert(game.get_player(event.player_index))
     local area = AABB.expand(event.area)
+    local area_size = AABB.size(area)
     local surface = event.surface
-    local area_size = (area.right_bottom.x - area.left_top.x) * (area.right_bottom.y - area.left_top.y)
 
     if area_size > 1000 then
         player.print({ "exp-commands_surface.area-too-large", 1000, area_size }, Commands.print_settings.error)
diff --git a/exp_scenario/module/commands/waterfill.lua b/exp_scenario/module/commands/waterfill.lua
index 4ca95ec9..6e1a8e24 100644
--- a/exp_scenario/module/commands/waterfill.lua
+++ b/exp_scenario/module/commands/waterfill.lua
@@ -41,6 +41,7 @@ commands.waterfill = Commands.new("waterfill", { "exp-commands_waterfill.descrip
 --- When an area is selected to be converted to water
 SelectArea:on_selection(function(event)
     local area = AABB.expand(event.area)
+    local area_size = AABB.size(area)
     local player = game.players[event.player_index]
     local surface = event.surface
 
@@ -51,8 +52,6 @@ SelectArea:on_selection(function(event)
     end
     ]]
 
-    local area_size = (area.right_bottom.x - area.left_top.x) * (area.right_bottom.y - area.left_top.y)
-
     if area_size > 1000 then
         player.print({ "exp-commands_waterfill.area-too-large", 1000, area_size }, Commands.print_settings.error)
         return
diff --git a/exp_util/module/aabb.lua b/exp_util/module/aabb.lua
index dda22d75..64c5719d 100644
--- a/exp_util/module/aabb.lua
+++ b/exp_util/module/aabb.lua
@@ -17,6 +17,13 @@ function AABB.valid(aabb)
     return aabb.left_top.x < aabb.right_bottom.x and aabb.left_top.y < aabb.right_bottom.y
 end
 
+--- Returns the size of the area contained within an AABB
+--- @param aabb BoundingBox
+--- @return number
+function AABB.size(aabb)
+    return (aabb.right_bottom.x - aabb.left_top.x) * (aabb.right_bottom.y - aabb.left_top.y)
+end
+
 --- Clone an area, allows for safe mutation of an input value
 --- @param aabb BoundingBox
 --- @return BoundingBox