diff --git a/flow/platforms/gf180/config.mk b/flow/platforms/gf180/config.mk
index d4fea42f7f..a8af3d4184 100644
--- a/flow/platforms/gf180/config.mk
+++ b/flow/platforms/gf180/config.mk
@@ -32,6 +32,10 @@ export FILL_CELLS                             ?= gf180mcu_fd_sc_mcu$(TRACK_OPTIO
                                                  gf180mcu_fd_sc_mcu$(TRACK_OPTION)$(POWER_OPTION)__fill_2 \
                                                  gf180mcu_fd_sc_mcu$(TRACK_OPTION)$(POWER_OPTION)__fill_1
 
+# Metal density fill rules (OpenROAD density_fill). Applied at chip level
+# only when USE_FILL=1; macro/block builds leave USE_FILL=0 (the default).
+export FILL_CONFIG                            ?= $(PLATFORM_DIR)/fill.json
+
 export TIE_CELL                               = gf180mcu_fd_sc_mcu$(TRACK_OPTION)$(POWER_OPTION)__filltie
 export ENDCAP_CELL                            = gf180mcu_fd_sc_mcu$(TRACK_OPTION)$(POWER_OPTION)__endcap
 export RC_FILE                                = $(PLATFORM_DIR)/setRC.tcl
diff --git a/flow/platforms/gf180/fill.json b/flow/platforms/gf180/fill.json
new file mode 100644
index 0000000000..a208c0c5be
--- /dev/null
+++ b/flow/platforms/gf180/fill.json
@@ -0,0 +1,78 @@
+{
+    "layers" : {
+        "Metal1" : {
+            "layer":                   34,
+            "name":                    "Metal1",
+            "dir":                     "H",
+            "datatype":                 0,
+            "space_to_outline":         5,
+            "non-opc": {
+                "datatype":             4,
+                "width":                [12.00, 6.00, 3.00, 2.00],
+                "height":               [2.00, 2.00, 2.00, 2.00],
+                "space_to_fill":        1.0,
+                "space_to_non_fill":    2.0
+            }
+        },
+
+        "Metal2" : {
+            "layer":                   36,
+            "name":                    "Metal2",
+            "dir":                     "V",
+            "datatype":                 0,
+            "space_to_outline":         5,
+            "non-opc": {
+                "datatype":             4,
+                "width":                [2.00, 2.00, 2.00, 2.00],
+                "height":               [12.00, 6.00, 3.00, 2.00],
+                "space_to_fill":        1.0,
+                "space_to_non_fill":    2.0
+            }
+        },
+
+        "Metal3" : {
+            "layer":                   42,
+            "name":                    "Metal3",
+            "dir":                     "H",
+            "datatype":                 0,
+            "space_to_outline":         5,
+            "non-opc": {
+                "datatype":             4,
+                "width":                [12.00, 6.00, 3.00, 2.00],
+                "height":               [2.00, 2.00, 2.00, 2.00],
+                "space_to_fill":        1.0,
+                "space_to_non_fill":    2.0
+            }
+        },
+
+        "Metal4" : {
+            "layer":                   46,
+            "name":                    "Metal4",
+            "dir":                     "V",
+            "datatype":                 0,
+            "space_to_outline":         5,
+            "non-opc": {
+                "datatype":             4,
+                "width":                [2.00, 2.00, 2.00, 2.00],
+                "height":               [12.00, 6.00, 3.00, 2.00],
+                "space_to_fill":        1.0,
+                "space_to_non_fill":    2.0
+            }
+        },
+
+        "Metal5" : {
+            "layer":                   81,
+            "name":                    "Metal5",
+            "dir":                     "H",
+            "datatype":                 0,
+            "space_to_outline":         5,
+            "non-opc": {
+                "datatype":             4,
+                "width":                [12.00, 6.00, 3.00, 2.00],
+                "height":               [2.00, 2.00, 2.00, 2.00],
+                "space_to_fill":        1.0,
+                "space_to_non_fill":    2.0
+            }
+        }
+    }
+}
diff --git a/flow/platforms/gf180/gds/7t/gf180mcu_5LM_1TM_9K_7t_edi2gds.layermap b/flow/platforms/gf180/gds/7t/gf180mcu_5LM_1TM_9K_7t_edi2gds.layermap
index d690d3ffe0..0239c803aa 100755
--- a/flow/platforms/gf180/gds/7t/gf180mcu_5LM_1TM_9K_7t_edi2gds.layermap
+++ b/flow/platforms/gf180/gds/7t/gf180mcu_5LM_1TM_9K_7t_edi2gds.layermap
@@ -6,8 +6,8 @@ Metal1		NET		34		0
 Metal1		SPNET		34		0
 Metal1		PIN		34		0
 Metal1		LEFPIN		34		0
-Metal1		FILL		34		0
-Metal1		FILLOPC		34		0
+Metal1		FILL		34		4
+Metal1		FILLOPC		34		4
 Metal1		VIA		34		0
 Metal1		VIAFILL		34		0
 Metal1		VIAFILLOPC	34		0
@@ -31,8 +31,8 @@ Metal2		NET		36		0
 Metal2		SPNET		36		0
 Metal2		PIN		36		0
 Metal2		LEFPIN		36		0
-Metal2		FILL		36		0
-Metal2		FILLOPC		36		0
+Metal2		FILL		36		4
+Metal2		FILLOPC		36		4
 Metal2		VIA		36		0
 Metal2		VIAFILL		36		0
 Metal2		VIAFILLOPC	36		0
@@ -56,8 +56,8 @@ Metal3		NET		42		0
 Metal3		SPNET		42		0
 Metal3		PIN		42		0
 Metal3		LEFPIN		42		0
-Metal3		FILL		42		0
-Metal3		FILLOPC		42		0
+Metal3		FILL		42		4
+Metal3		FILLOPC		42		4
 Metal3		VIA		42		0
 Metal3		VIAFILL		42		0
 Metal3		VIAFILLOPC	42		0
@@ -81,8 +81,8 @@ Metal4		NET		46		0
 Metal4		SPNET		46		0
 Metal4		PIN		46		0
 Metal4		LEFPIN		46		0
-Metal4		FILL		46		0
-Metal4		FILLOPC		46		0
+Metal4		FILL		46		4
+Metal4		FILLOPC		46		4
 Metal4		VIA		46		0
 Metal4		VIAFILL		46		0
 Metal4		VIAFILLOPC	46		0
@@ -106,8 +106,8 @@ Metal5		NET		81		0
 Metal5		SPNET		81		0
 Metal5		PIN		81		0
 Metal5		LEFPIN		81		0
-Metal5		FILL		81		0
-Metal5		FILLOPC		81		0
+Metal5		FILL		81		4
+Metal5		FILLOPC		81		4
 Metal5		VIA		81		0
 Metal5		VIAFILL		81		0
 Metal5		VIAFILLOPC	81		0
diff --git a/flow/platforms/gf180/gds/7t/gf180mcu_6LM_1TM_9K_7t_edi2gds.layermap b/flow/platforms/gf180/gds/7t/gf180mcu_6LM_1TM_9K_7t_edi2gds.layermap
index 67b85e06c1..1c60f62d19 100755
--- a/flow/platforms/gf180/gds/7t/gf180mcu_6LM_1TM_9K_7t_edi2gds.layermap
+++ b/flow/platforms/gf180/gds/7t/gf180mcu_6LM_1TM_9K_7t_edi2gds.layermap
@@ -6,8 +6,8 @@ Metal1		NET		34		0
 Metal1		SPNET		34		0
 Metal1		PIN		34		0
 Metal1		LEFPIN		34		0
-Metal1		FILL		34		0
-Metal1		FILLOPC		34		0
+Metal1		FILL		34		4
+Metal1		FILLOPC		34		4
 Metal1		VIA		34		0
 Metal1		VIAFILL		34		0
 Metal1		VIAFILLOPC	34		0
@@ -31,8 +31,8 @@ Metal2		NET		36		0
 Metal2		SPNET		36		0
 Metal2		PIN		36		0
 Metal2		LEFPIN		36		0
-Metal2		FILL		36		0
-Metal2		FILLOPC		36		0
+Metal2		FILL		36		4
+Metal2		FILLOPC		36		4
 Metal2		VIA		36		0
 Metal2		VIAFILL		36		0
 Metal2		VIAFILLOPC	36		0
@@ -56,8 +56,8 @@ Metal3		NET		42		0
 Metal3		SPNET		42		0
 Metal3		PIN		42		0
 Metal3		LEFPIN		42		0
-Metal3		FILL		42		0
-Metal3		FILLOPC		42		0
+Metal3		FILL		42		4
+Metal3		FILLOPC		42		4
 Metal3		VIA		42		0
 Metal3		VIAFILL		42		0
 Metal3		VIAFILLOPC	42		0
@@ -81,8 +81,8 @@ Metal4		NET		46		0
 Metal4		SPNET		46		0
 Metal4		PIN		46		0
 Metal4		LEFPIN		46		0
-Metal4		FILL		46		0
-Metal4		FILLOPC		46		0
+Metal4		FILL		46		4
+Metal4		FILLOPC		46		4
 Metal4		VIA		46		0
 Metal4		VIAFILL		46		0
 Metal4		VIAFILLOPC	46		0
@@ -106,8 +106,8 @@ Metal5		NET		81		0
 Metal5		SPNET		81		0
 Metal5		PIN		81		0
 Metal5		LEFPIN		81		0
-Metal5		FILL		81		0
-Metal5		FILLOPC		81		0
+Metal5		FILL		81		4
+Metal5		FILLOPC		81		4
 Metal5		VIA		81		0
 Metal5		VIAFILL		81		0
 Metal5		VIAFILLOPC	81		0
diff --git a/flow/platforms/gf180/gds/9t/gf180mcu_5LM_1TM_9K_9t_edi2gds.layermap b/flow/platforms/gf180/gds/9t/gf180mcu_5LM_1TM_9K_9t_edi2gds.layermap
index d690d3ffe0..0239c803aa 100755
--- a/flow/platforms/gf180/gds/9t/gf180mcu_5LM_1TM_9K_9t_edi2gds.layermap
+++ b/flow/platforms/gf180/gds/9t/gf180mcu_5LM_1TM_9K_9t_edi2gds.layermap
@@ -6,8 +6,8 @@ Metal1		NET		34		0
 Metal1		SPNET		34		0
 Metal1		PIN		34		0
 Metal1		LEFPIN		34		0
-Metal1		FILL		34		0
-Metal1		FILLOPC		34		0
+Metal1		FILL		34		4
+Metal1		FILLOPC		34		4
 Metal1		VIA		34		0
 Metal1		VIAFILL		34		0
 Metal1		VIAFILLOPC	34		0
@@ -31,8 +31,8 @@ Metal2		NET		36		0
 Metal2		SPNET		36		0
 Metal2		PIN		36		0
 Metal2		LEFPIN		36		0
-Metal2		FILL		36		0
-Metal2		FILLOPC		36		0
+Metal2		FILL		36		4
+Metal2		FILLOPC		36		4
 Metal2		VIA		36		0
 Metal2		VIAFILL		36		0
 Metal2		VIAFILLOPC	36		0
@@ -56,8 +56,8 @@ Metal3		NET		42		0
 Metal3		SPNET		42		0
 Metal3		PIN		42		0
 Metal3		LEFPIN		42		0
-Metal3		FILL		42		0
-Metal3		FILLOPC		42		0
+Metal3		FILL		42		4
+Metal3		FILLOPC		42		4
 Metal3		VIA		42		0
 Metal3		VIAFILL		42		0
 Metal3		VIAFILLOPC	42		0
@@ -81,8 +81,8 @@ Metal4		NET		46		0
 Metal4		SPNET		46		0
 Metal4		PIN		46		0
 Metal4		LEFPIN		46		0
-Metal4		FILL		46		0
-Metal4		FILLOPC		46		0
+Metal4		FILL		46		4
+Metal4		FILLOPC		46		4
 Metal4		VIA		46		0
 Metal4		VIAFILL		46		0
 Metal4		VIAFILLOPC	46		0
@@ -106,8 +106,8 @@ Metal5		NET		81		0
 Metal5		SPNET		81		0
 Metal5		PIN		81		0
 Metal5		LEFPIN		81		0
-Metal5		FILL		81		0
-Metal5		FILLOPC		81		0
+Metal5		FILL		81		4
+Metal5		FILLOPC		81		4
 Metal5		VIA		81		0
 Metal5		VIAFILL		81		0
 Metal5		VIAFILLOPC	81		0
diff --git a/flow/platforms/gf180/gds/9t/gf180mcu_6LM_1TM_9K_9t_edi2gds.layermap b/flow/platforms/gf180/gds/9t/gf180mcu_6LM_1TM_9K_9t_edi2gds.layermap
index 67b85e06c1..1c60f62d19 100755
--- a/flow/platforms/gf180/gds/9t/gf180mcu_6LM_1TM_9K_9t_edi2gds.layermap
+++ b/flow/platforms/gf180/gds/9t/gf180mcu_6LM_1TM_9K_9t_edi2gds.layermap
@@ -6,8 +6,8 @@ Metal1		NET		34		0
 Metal1		SPNET		34		0
 Metal1		PIN		34		0
 Metal1		LEFPIN		34		0
-Metal1		FILL		34		0
-Metal1		FILLOPC		34		0
+Metal1		FILL		34		4
+Metal1		FILLOPC		34		4
 Metal1		VIA		34		0
 Metal1		VIAFILL		34		0
 Metal1		VIAFILLOPC	34		0
@@ -31,8 +31,8 @@ Metal2		NET		36		0
 Metal2		SPNET		36		0
 Metal2		PIN		36		0
 Metal2		LEFPIN		36		0
-Metal2		FILL		36		0
-Metal2		FILLOPC		36		0
+Metal2		FILL		36		4
+Metal2		FILLOPC		36		4
 Metal2		VIA		36		0
 Metal2		VIAFILL		36		0
 Metal2		VIAFILLOPC	36		0
@@ -56,8 +56,8 @@ Metal3		NET		42		0
 Metal3		SPNET		42		0
 Metal3		PIN		42		0
 Metal3		LEFPIN		42		0
-Metal3		FILL		42		0
-Metal3		FILLOPC		42		0
+Metal3		FILL		42		4
+Metal3		FILLOPC		42		4
 Metal3		VIA		42		0
 Metal3		VIAFILL		42		0
 Metal3		VIAFILLOPC	42		0
@@ -81,8 +81,8 @@ Metal4		NET		46		0
 Metal4		SPNET		46		0
 Metal4		PIN		46		0
 Metal4		LEFPIN		46		0
-Metal4		FILL		46		0
-Metal4		FILLOPC		46		0
+Metal4		FILL		46		4
+Metal4		FILLOPC		46		4
 Metal4		VIA		46		0
 Metal4		VIAFILL		46		0
 Metal4		VIAFILLOPC	46		0
@@ -106,8 +106,8 @@ Metal5		NET		81		0
 Metal5		SPNET		81		0
 Metal5		PIN		81		0
 Metal5		LEFPIN		81		0
-Metal5		FILL		81		0
-Metal5		FILLOPC		81		0
+Metal5		FILL		81		4
+Metal5		FILLOPC		81		4
 Metal5		VIA		81		0
 Metal5		VIAFILL		81		0
 Metal5		VIAFILLOPC	81		0