diff --git a/src/ai/ai_gui.cpp b/src/ai/ai_gui.cpp
index b4808061b3..b37bcd17f4 100644
--- a/src/ai/ai_gui.cpp
+++ b/src/ai/ai_gui.cpp
@@ -205,7 +205,7 @@ struct AIListWindow : public Window {
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / this->line_height);
+		this->vscroll.SetCapacity(this->GetWidget<NWidgetCore>(AIL_WIDGET_LIST)->current_y / this->line_height);
 		this->GetWidget<NWidgetCore>(AIL_WIDGET_LIST)->widget_data = (this->vscroll.GetCapacity() << MAT_ROW_START) + (1 << MAT_COL_START);
 	}
 };
@@ -401,7 +401,7 @@ struct AISettingsWindow : public Window {
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / this->line_height);
+		this->vscroll.SetCapacity(this->GetWidget<NWidgetCore>(AIS_WIDGET_BACKGROUND)->current_y / this->line_height);
 		this->GetWidget<NWidgetCore>(AIS_WIDGET_BACKGROUND)->widget_data = (this->vscroll.GetCapacity() << MAT_ROW_START) + (1 << MAT_COL_START);
 	}
 
@@ -662,8 +662,6 @@ struct AIDebugWindow : public Window {
 
 	AIDebugWindow(const WindowDesc *desc, WindowNumber number) : Window()
 	{
-		this->vscroll.SetCapacity(14); // Minimal number of lines in the log panel.
-
 		this->InitNested(desc, number);
 		/* Disable the companies who are not active or not an AI */
 		for (CompanyID i = COMPANY_FIRST; i < MAX_COMPANIES; i++) {
@@ -671,6 +669,8 @@ struct AIDebugWindow : public Window {
 		}
 		this->DisableWidget(AID_WIDGET_RELOAD_TOGGLE);
 
+		this->vscroll.SetCapacity(this->GetWidget<NWidgetBase>(AID_WIDGET_LOG_PANEL)->current_y / this->resize.step_height);
+
 		this->last_vscroll_pos = 0;
 		this->autoscroll = true;
 
@@ -681,7 +681,7 @@ struct AIDebugWindow : public Window {
 	{
 		if (widget == AID_WIDGET_LOG_PANEL) {
 			resize->height = FONT_HEIGHT_NORMAL + WD_PAR_VSEP_NORMAL;
-			size->height = this->vscroll.GetCapacity() * resize->height + this->top_offset + this->bottom_offset;
+			size->height = 14 * resize->height + this->top_offset + this->bottom_offset;
 		}
 	}
 
@@ -878,7 +878,7 @@ struct AIDebugWindow : public Window {
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / (int)this->resize.step_height);
+		this->vscroll.SetCapacity(this->GetWidget<NWidgetBase>(AID_WIDGET_LOG_PANEL)->current_y / this->resize.step_height);
 	}
 };
 
diff --git a/src/bridge_gui.cpp b/src/bridge_gui.cpp
index 806f1fd2c5..444d428486 100644
--- a/src/bridge_gui.cpp
+++ b/src/bridge_gui.cpp
@@ -284,7 +284,7 @@ public:
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / (int)this->resize.step_height);
+		this->vscroll.SetCapacity(this->GetWidget<NWidgetBase>(BBSW_BRIDGE_LIST)->current_y / this->resize.step_height);
 		this->GetWidget<NWidgetCore>(BBSW_BRIDGE_LIST)->widget_data = (this->vscroll.GetCapacity() << MAT_ROW_START) + (1 << MAT_COL_START);
 
 		this->last_size = max(this->vscroll.GetCapacity(), this->last_size);
diff --git a/src/build_vehicle_gui.cpp b/src/build_vehicle_gui.cpp
index a6920a9253..a2af9cfe22 100644
--- a/src/build_vehicle_gui.cpp
+++ b/src/build_vehicle_gui.cpp
@@ -1177,7 +1177,7 @@ struct BuildVehicleWindow : Window {
 		}
 		if (delta.y == 0) return;
 
-		this->vscroll.UpdateCapacity(delta.y / (int)GetVehicleListHeight(this->vehicle_type));
+		this->vscroll.SetCapacity((this->widget[BUILD_VEHICLE_WIDGET_LIST].bottom - this->widget[BUILD_VEHICLE_WIDGET_LIST].top + 1) / GetVehicleListHeight(this->vehicle_type));
 		this->widget[BUILD_VEHICLE_WIDGET_LIST].data = (this->vscroll.GetCapacity() << MAT_ROW_START) + (1 << MAT_COL_START);
 	}
 };
diff --git a/src/depot_gui.cpp b/src/depot_gui.cpp
index d61a3fa874..671a97f6fd 100644
--- a/src/depot_gui.cpp
+++ b/src/depot_gui.cpp
@@ -906,8 +906,8 @@ struct DepotWindow : Window {
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / (int)this->resize.step_height);
-		this->hscroll.UpdateCapacity(delta.x / (int)this->resize.step_width);
+		this->vscroll.SetCapacity(this->GetWidget<NWidgetCore>(DEPOT_WIDGET_MATRIX)->current_y / (int)this->resize.step_height);
+		this->hscroll.SetCapacity(this->GetWidget<NWidgetCore>(DEPOT_WIDGET_MATRIX)->current_x / (int)this->resize.step_width);
 		this->GetWidget<NWidgetCore>(DEPOT_WIDGET_MATRIX)->widget_data = (this->vscroll.GetCapacity() << MAT_ROW_START) +
 											((this->type == VEH_TRAIN ? 1 : this->hscroll.GetCapacity()) << MAT_COL_START);
 	}
diff --git a/src/group_gui.cpp b/src/group_gui.cpp
index 8c31e47140..4ec91214e1 100644
--- a/src/group_gui.cpp
+++ b/src/group_gui.cpp
@@ -614,10 +614,10 @@ public:
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll2.UpdateCapacity(delta.y / PLY_WND_PRC__SIZE_OF_ROW_TINY);
-		this->vscroll.UpdateCapacity(delta.y / (int)this->resize.step_height);
-
+		this->vscroll2.SetCapacity((this->widget[GRP_WIDGET_LIST_GROUP].bottom - this->widget[GRP_WIDGET_LIST_GROUP].top + 1) / PLY_WND_PRC__SIZE_OF_ROW_TINY);
 		this->widget[GRP_WIDGET_LIST_GROUP].data = (this->vscroll2.GetCapacity() << MAT_ROW_START) + (1 << MAT_COL_START);
+
+		this->vscroll.SetCapacity((this->widget[GRP_WIDGET_LIST_VEHICLE].bottom - this->widget[GRP_WIDGET_LIST_VEHICLE].top + 1) / this->resize.step_height);
 		this->widget[GRP_WIDGET_LIST_VEHICLE].data = (this->vscroll.GetCapacity() << MAT_ROW_START) + (1 << MAT_COL_START);
 	}
 
diff --git a/src/industry_gui.cpp b/src/industry_gui.cpp
index 84b5b11048..365e2da8e5 100644
--- a/src/industry_gui.cpp
+++ b/src/industry_gui.cpp
@@ -361,7 +361,7 @@ public:
 	virtual void OnResize(Point delta)
 	{
 		/* Adjust the number of items in the matrix depending of the rezise */
-		this->vscroll.UpdateCapacity(delta.y / (int)this->resize.step_height);
+		this->vscroll.SetCapacity((this->widget[DPIW_MATRIX_WIDGET].bottom - this->widget[DPIW_MATRIX_WIDGET].top + 1) / this->resize.step_height);
 		this->widget[DPIW_MATRIX_WIDGET].data = (this->vscroll.GetCapacity() << MAT_ROW_START) + (1 << MAT_COL_START);
 	}
 
@@ -1050,7 +1050,7 @@ public:
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / (int)this->resize.step_height);
+		this->vscroll.SetCapacity(this->GetWidget<NWidgetBase>(IDW_INDUSTRY_LIST)->current_y / this->resize.step_height);
 	}
 
 	virtual void OnHundredthTick()
diff --git a/src/misc_gui.cpp b/src/misc_gui.cpp
index 0085e42832..3150e1cae1 100644
--- a/src/misc_gui.cpp
+++ b/src/misc_gui.cpp
@@ -1857,7 +1857,7 @@ public:
 
 			case SLD_LOAD_SCENARIO:
 			case SLD_LOAD_HEIGHTMAP:
-				this->vscroll.UpdateCapacity(-1);
+				this->vscroll.SetCapacity(this->vscroll.GetCapacity() - 1);
 
 			case SLD_SAVE_GAME:     this->GenerateFileName(); break;
 			case SLD_SAVE_SCENARIO: strecpy(this->edit_str_buf, "UNNAMED", &this->edit_str_buf[edit_str_size - 1]); break;
@@ -1974,7 +1974,7 @@ public:
 				break;
 
 			case SLWW_DRIVES_DIRECTORIES_LIST: { // Click the listbox
-				int y = (pt.y - this->widget[widget].top - 1) / 10;
+				int y = (pt.y - this->widget[SLWW_DRIVES_DIRECTORIES_LIST].top - 1) / 10;
 
 				if (y < 0 || (y += this->vscroll.GetPosition()) >= this->vscroll.GetCount()) return;
 
@@ -2092,7 +2092,7 @@ public:
 			this->widget[SLWW_SAVE_GAME].left  += diff;
 		}
 
-		this->vscroll.UpdateCapacity(delta.y / 10);
+		this->vscroll.SetCapacity((this->widget[SLWW_DRIVES_DIRECTORIES_LIST].bottom - this->widget[SLWW_DRIVES_DIRECTORIES_LIST].top + 1) / 10);
 	}
 
 	virtual void OnInvalidateData(int data)
diff --git a/src/network/network_content_gui.cpp b/src/network/network_content_gui.cpp
index 906796eb80..1a71964e69 100644
--- a/src/network/network_content_gui.cpp
+++ b/src/network/network_content_gui.cpp
@@ -692,7 +692,7 @@ public:
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / (int)this->resize.step_height);
+		this->vscroll.SetCapacity((this->widget[NCLWW_MATRIX].bottom - this->widget[NCLWW_MATRIX].top + 1) / this->resize.step_height);
 		this->widget[NCLWW_MATRIX].data = (this->vscroll.GetCapacity() << MAT_ROW_START) + (1 << MAT_COL_START);
 
 		/* Make the matrix and details section grow both bigger (or smaller) */
diff --git a/src/network/network_gui.cpp b/src/network/network_gui.cpp
index 085be44d8f..85ee499b80 100644
--- a/src/network/network_gui.cpp
+++ b/src/network/network_gui.cpp
@@ -714,7 +714,7 @@ public:
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / (int)this->resize.step_height);
+		this->vscroll.SetCapacity((this->widget[NGWW_MATRIX].bottom - this->widget[NGWW_MATRIX].top + 1) / this->resize.step_height);
 		this->widget[NGWW_MATRIX].data = (this->vscroll.GetCapacity() << MAT_ROW_START) + (1 << MAT_COL_START);
 
 		/* Additional colums in server list */
diff --git a/src/newgrf_gui.cpp b/src/newgrf_gui.cpp
index 5f4171c81e..c486e36b59 100644
--- a/src/newgrf_gui.cpp
+++ b/src/newgrf_gui.cpp
@@ -281,7 +281,7 @@ public:
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / (int)this->resize.step_height);
+		this->vscroll.SetCapacity(this->GetWidget<NWidgetBase>(ANGRFW_GRF_LIST)->current_y / this->resize.step_height);
 	}
 
 	virtual void OnPaint()
@@ -610,7 +610,7 @@ struct NewGRFWindow : public Window {
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / (int)this->resize.step_height);
+		this->vscroll.SetCapacity(this->GetWidget<NWidgetCore>(SNGRFS_FILE_LIST)->current_y / this->resize.step_height);
 		this->GetWidget<NWidgetCore>(SNGRFS_FILE_LIST)->widget_data = (this->vscroll.GetCapacity() << MAT_ROW_START) + (1 << MAT_COL_START);
 	}
 
diff --git a/src/news_gui.cpp b/src/news_gui.cpp
index c9992eb1af..ed78df793c 100644
--- a/src/news_gui.cpp
+++ b/src/news_gui.cpp
@@ -993,7 +993,7 @@ struct MessageHistoryWindow : Window {
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / this->line_height);
+		this->vscroll.SetCapacity(this->GetWidget<NWidgetBase>(MHW_BACKGROUND)->current_y / this->line_height);
 	}
 };
 
diff --git a/src/order_gui.cpp b/src/order_gui.cpp
index fc6d60cef2..e985b4f215 100644
--- a/src/order_gui.cpp
+++ b/src/order_gui.cpp
@@ -1268,8 +1268,8 @@ public:
 
 	virtual void OnResize(Point delta)
 	{
-		/* Update the scroll + matrix */
-		this->vscroll.UpdateCapacity(delta.y / (int)this->resize.step_height);
+		/* Update the scroll bar */
+		this->vscroll.SetCapacity(this->GetWidget<NWidgetBase>(ORDER_WIDGET_ORDER_LIST)->current_y / this->resize.step_height);
 	}
 
 	virtual void OnTimeout()
diff --git a/src/settings_gui.cpp b/src/settings_gui.cpp
index 20864302c1..3315b6428b 100644
--- a/src/settings_gui.cpp
+++ b/src/settings_gui.cpp
@@ -1625,7 +1625,7 @@ struct GameSettingsWindow : Window {
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / SETTING_HEIGHT);
+		this->vscroll.SetCapacity((this->widget[SETTINGSEL_OPTIONSPANEL].bottom - this->widget[SETTINGSEL_OPTIONSPANEL].top - 8) / SETTING_HEIGHT);
 	}
 };
 
diff --git a/src/signs_gui.cpp b/src/signs_gui.cpp
index 2143455061..1ff7c928bf 100644
--- a/src/signs_gui.cpp
+++ b/src/signs_gui.cpp
@@ -157,7 +157,7 @@ struct SignListWindow : Window, SignList {
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / (int)this->resize.step_height);
+		this->vscroll.SetCapacity((this->GetWidget<NWidgetBase>(SLW_LIST)->current_y - WD_FRAMERECT_TOP - WD_FRAMERECT_BOTTOM) / this->resize.step_height);
 	}
 
 	virtual void UpdateWidgetSize(int widget, Dimension *size, const Dimension &padding, Dimension *resize)
diff --git a/src/station_gui.cpp b/src/station_gui.cpp
index 01e1caa630..3ab59320a5 100644
--- a/src/station_gui.cpp
+++ b/src/station_gui.cpp
@@ -566,7 +566,7 @@ public:
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / 10);
+		this->vscroll.SetCapacity((this->widget[SLW_LIST].bottom - this->widget[SLW_LIST].top + 1) / 10);
 	}
 
 	virtual void OnInvalidateData(int data)
@@ -1052,7 +1052,7 @@ struct StationViewWindow : public Window {
 	virtual void OnResize(Point delta)
 	{
 		if (delta.x != 0) ResizeButtons(this, SVW_LOCATION, SVW_RENAME);
-		this->vscroll.UpdateCapacity(delta.y / (int)this->resize.step_height);
+		this->vscroll.SetCapacity((this->widget[SVW_WAITING].bottom - this->widget[SVW_WAITING].top + 1) / this->resize.step_height);
 	}
 };
 
@@ -1296,7 +1296,7 @@ struct SelectStationWindow : Window {
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / (int)this->resize.step_height);
+		this->vscroll.SetCapacity((this->GetWidget<NWidgetBase>(JSW_PANEL)->current_y - WD_FRAMERECT_TOP - WD_FRAMERECT_BOTTOM) / this->resize.step_height);
 	}
 
 	virtual void OnInvalidateData(int data)
diff --git a/src/subsidy_gui.cpp b/src/subsidy_gui.cpp
index 5754464a39..ca8b38a340 100644
--- a/src/subsidy_gui.cpp
+++ b/src/subsidy_gui.cpp
@@ -222,7 +222,7 @@ struct SubsidyListWindow : Window {
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / (int)this->resize.step_height);
+		this->vscroll.SetCapacity(this->GetWidget<NWidgetBase>(SLW_PANEL)->current_y / this->resize.step_height);
 	}
 
 	virtual void OnInvalidateData(int data)
diff --git a/src/timetable_gui.cpp b/src/timetable_gui.cpp
index 29f4b76af2..65a2dd7b83 100644
--- a/src/timetable_gui.cpp
+++ b/src/timetable_gui.cpp
@@ -333,8 +333,8 @@ struct TimetableWindow : Window {
 
 	virtual void OnResize(Point delta)
 	{
-		/* Update the scroll + matrix */
-		this->vscroll.UpdateCapacity(delta.y / 10);
+		/* Update the scroll bar */
+		this->vscroll.SetCapacity((this->widget[TTV_TIMETABLE_PANEL].bottom - this->widget[TTV_TIMETABLE_PANEL].top + 1) / this->resize.step_height);
 	}
 };
 
diff --git a/src/town_gui.cpp b/src/town_gui.cpp
index be0a0d4b41..138cb81bb2 100644
--- a/src/town_gui.cpp
+++ b/src/town_gui.cpp
@@ -659,7 +659,7 @@ public:
 		this->BuildSortTownList();
 
 		this->InitNested(desc, 0);
-		this->vscroll.SetCapacity(this->GetWidget<NWidgetBase>(TDW_CENTERTOWN)->current_y / (int)this->resize.step_height);
+		this->vscroll.SetCapacity(this->GetWidget<NWidgetBase>(TDW_CENTERTOWN)->current_y / this->resize.step_height);
 	}
 
 	~TownDirectoryWindow()
@@ -803,7 +803,7 @@ public:
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / (int)this->resize.step_height);
+		this->vscroll.SetCapacity(this->GetWidget<NWidgetBase>(TDW_CENTERTOWN)->current_y / this->resize.step_height);
 	}
 
 	virtual void OnInvalidateData(int data)
diff --git a/src/vehicle_gui.cpp b/src/vehicle_gui.cpp
index 4af37ff2c8..f2cb72cd5e 100644
--- a/src/vehicle_gui.cpp
+++ b/src/vehicle_gui.cpp
@@ -389,7 +389,7 @@ struct RefitWindow : public Window {
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / (int)this->resize.step_height);
+		this->vscroll.SetCapacity((this->widget[VRW_MATRIX].bottom - this->widget[VRW_MATRIX].top + 1) / this->resize.step_height);
 		this->widget[VRW_MATRIX].data = (this->vscroll.GetCapacity() << MAT_ROW_START) + (1 << MAT_COL_START);
 	}
 };
@@ -1105,7 +1105,7 @@ struct VehicleListWindow : public BaseVehicleListWindow {
 
 	virtual void OnResize(Point delta)
 	{
-		this->vscroll.UpdateCapacity(delta.y / (int)this->resize.step_height);
+		this->vscroll.SetCapacity((this->widget[VLW_WIDGET_LIST].bottom - this->widget[VLW_WIDGET_LIST].top + 1) / this->resize.step_height);
 		this->widget[VLW_WIDGET_LIST].data = (this->vscroll.GetCapacity() << MAT_ROW_START) + (1 << MAT_COL_START);
 	}
 
@@ -1501,7 +1501,7 @@ struct VehicleDetailsWindow : Window {
 		if (delta.x != 0) ResizeButtons(this, VLD_WIDGET_DETAILS_CARGO_CARRIED, VLD_WIDGET_DETAILS_TOTAL_CARGO);
 		if (delta.y == 0) return;
 
-		this->vscroll.UpdateCapacity(delta.y / 14);
+		this->vscroll.SetCapacity((this->widget[VLD_WIDGET_MIDDLE_DETAILS].bottom - this->widget[VLD_WIDGET_MIDDLE_DETAILS].top + 1) / 14);
 		this->widget[VLD_WIDGET_MIDDLE_DETAILS].data = (this->vscroll.GetCapacity() << MAT_ROW_START) + (1 << MAT_COL_START);
 	}
 };
diff --git a/src/window_gui.h b/src/window_gui.h
index 2e9b590b85..4204ec9cdf 100644
--- a/src/window_gui.h
+++ b/src/window_gui.h
@@ -257,17 +257,6 @@ public:
 		if (this->cap + this->pos > this->count) this->pos = max(0, this->count - this->cap);
 	}
 
-	/**
-	 * Updates the capacity by adding/removing a number of (visible) elements.
-	 * @param difference the difference in capacity
-	 * @note updates the position if needed
-	 */
-	void UpdateCapacity(int difference)
-	{
-		if (difference == 0) return;
-		this->SetCapacity(this->cap + difference);
-	}
-
 	/**
 	 * Sets the position of the first visible element
 	 * @param position the position of the element