diff --git a/src/gui/gsc_executor_log_window.cpp b/src/gui/gsc_executor_log_window.cpp
index 55f04d1..fb74830 100644
--- a/src/gui/gsc_executor_log_window.cpp
+++ b/src/gui/gsc_executor_log_window.cpp
@@ -31,6 +31,19 @@ Copyright:
 GscExecutorLogWindow::GscExecutorLogWindow(BaseObjectType* gtkcobj, Glib::RefPtr<Gtk::Builder> ui)
 		: AppBuilderWidget<GscExecutorLogWindow, false>(gtkcobj, std::move(ui))
 {
+	// Apply fractional scaling adjustment on Windows to default window size
+	// This compensates for GTK3's lack of fractional scaling support
+	const int fraction_percent = app_get_windows_fractional_scaling_percent();
+	if (fraction_percent > 0) {
+		int glade_w = 0, glade_h = 0;
+		get_default_size(glade_w, glade_h);
+		if (glade_w > 0 && glade_h > 0) {
+			const int scaled_w = static_cast<int>(glade_w * (1.0 + fraction_percent / 100.0));
+			const int scaled_h = static_cast<int>(glade_h * (1.0 + fraction_percent / 100.0));
+			set_default_size(scaled_w, scaled_h);
+		}
+	}
+
 	// Connect callbacks
 
 	Gtk::Button* window_close_button = nullptr;
diff --git a/src/gui/gsc_info_window.cpp b/src/gui/gsc_info_window.cpp
index ae32000..b6ec702 100644
--- a/src/gui/gsc_info_window.cpp
+++ b/src/gui/gsc_info_window.cpp
@@ -35,6 +35,7 @@ Copyright:
 #include "gsc_info_window.h"
 #include "gsc_executor_error_dialog.h"
 #include "gsc_startup_settings.h"
+#include "gsc_init.h"  // app_get_windows_fractional_scaling_percent()
 
 
 
@@ -164,8 +165,22 @@ GscInfoWindow::GscInfoWindow(BaseObjectType* gtkcobj, Glib::RefPtr<Gtk::Builder>
 {
 	// Size
 	{
-		const int def_size_w = rconfig::get_data<int>("gui/info_window/default_size_w");
-		const int def_size_h = rconfig::get_data<int>("gui/info_window/default_size_h");
+		int def_size_w = rconfig::get_data<int>("gui/info_window/default_size_w");
+		int def_size_h = rconfig::get_data<int>("gui/info_window/default_size_h");
+
+		// Apply fractional scaling adjustment on Windows if no custom size is configured
+		// This compensates for GTK3's lack of fractional scaling support
+		const int fraction_percent = app_get_windows_fractional_scaling_percent();
+		if (fraction_percent > 0 && def_size_w == 0 && def_size_h == 0) {
+			// Get the default size from glade and scale it
+			int glade_w = 0, glade_h = 0;
+			get_default_size(glade_w, glade_h);
+			if (glade_w > 0 && glade_h > 0) {
+				def_size_w = static_cast<int>(glade_w * (1.0 + fraction_percent / 100.0));
+				def_size_h = static_cast<int>(glade_h * (1.0 + fraction_percent / 100.0));
+			}
+		}
+
 		if (def_size_w > 0 && def_size_h > 0) {
 			set_default_size(def_size_w, def_size_h);
 		}
diff --git a/src/gui/gsc_init.cpp b/src/gui/gsc_init.cpp
index 0dff60c..d333e60 100644
--- a/src/gui/gsc_init.cpp
+++ b/src/gui/gsc_init.cpp
@@ -80,6 +80,10 @@ namespace {
 		return channel;
 	}
 
+
+	/// Storage for Windows fractional scaling percentage (0 if no fractional scaling)
+	inline int g_windows_fractional_scaling_percent = 0;
+
 }
 
 
@@ -91,6 +95,13 @@ std::string app_get_debug_buffer_str()
 
 
 
+int app_get_windows_fractional_scaling_percent()
+{
+	return g_windows_fractional_scaling_percent;
+}
+
+
+
 
 
 namespace {
@@ -521,6 +532,8 @@ bool app_init_and_loop(int& argc, char**& argv)
 			debug_out_info("app", "Windows system DPI: " << h_ppi << ", scale: " << scale << "\n");
 			const int fraction_percent = static_cast<int>(std::round(scale * 100)) % 100;
 			if (fraction_percent != 0) {  // fractional scaling
+				// Store for use in window sizing
+				g_windows_fractional_scaling_percent = fraction_percent;
 				// Increase the font size by fraction, but round down the size to match the Windows behavior (?)
 				debug_out_dump("app", "Fractional scaling detected, increasing font size by " << fraction_percent << "%.\n");
 				Gtk::Settings::get_default()->property_gtk_font_name()
diff --git a/src/gui/gsc_init.h b/src/gui/gsc_init.h
index b0ae517..f2f6b49 100644
--- a/src/gui/gsc_init.h
+++ b/src/gui/gsc_init.h
@@ -28,6 +28,11 @@ void app_quit();
 std::string app_get_debug_buffer_str();
 
 
+/// Get the fractional scaling percentage detected on Windows (0 if not detected).
+/// For example, at 150% scaling, this returns 50; at 125% scaling, this returns 25.
+int app_get_windows_fractional_scaling_percent();
+
+
 
 #endif
 
diff --git a/src/gui/gsc_main_window.cpp b/src/gui/gsc_main_window.cpp
index f784f39..cfe640e 100644
--- a/src/gui/gsc_main_window.cpp
+++ b/src/gui/gsc_main_window.cpp
@@ -58,8 +58,22 @@ GscMainWindow::GscMainWindow(BaseObjectType* gtkcobj, Glib::RefPtr<Gtk::Builder>
 
 	// Size
 	{
-		const int def_size_w = rconfig::get_data<int>("gui/main_window/default_size_w");
-		const int def_size_h = rconfig::get_data<int>("gui/main_window/default_size_h");
+		int def_size_w = rconfig::get_data<int>("gui/main_window/default_size_w");
+		int def_size_h = rconfig::get_data<int>("gui/main_window/default_size_h");
+
+		// Apply fractional scaling adjustment on Windows if no custom size is configured
+		// This compensates for GTK3's lack of fractional scaling support
+		const int fraction_percent = app_get_windows_fractional_scaling_percent();
+		if (fraction_percent > 0 && def_size_w == 0 && def_size_h == 0) {
+			// Get the default size from glade and scale it
+			int glade_w = 0, glade_h = 0;
+			get_default_size(glade_w, glade_h);
+			if (glade_w > 0 && glade_h > 0) {
+				def_size_w = static_cast<int>(glade_w * (1.0 + fraction_percent / 100.0));
+				def_size_h = static_cast<int>(glade_h * (1.0 + fraction_percent / 100.0));
+			}
+		}
+
 		if (def_size_w > 0 && def_size_h > 0) {
 			set_default_size(def_size_w, def_size_h);
 		}
diff --git a/src/gui/gsc_text_window.h b/src/gui/gsc_text_window.h
index 3b1cf0e..5d3b0c5 100644
--- a/src/gui/gsc_text_window.h
+++ b/src/gui/gsc_text_window.h
@@ -24,6 +24,7 @@ Copyright:
 
 #include "applib/app_builder_widget.h"
 #include "applib/app_gtkmm_tools.h"
+#include "gsc_init.h"  // app_get_windows_fractional_scaling_percent()
 
 
 
@@ -49,6 +50,19 @@ class GscTextWindow : public AppBuilderWidget<GscTextWindow<InstanceSwitch>, Ins
 		GscTextWindow(typename Gtk::Window::BaseObjectType* gtkcobj, Glib::RefPtr<Gtk::Builder> ui)
 				: AppBuilderWidget<GscTextWindow<InstanceSwitch>, InstanceSwitch::multi_instance>(gtkcobj, std::move(ui))
 		{
+			// Apply fractional scaling adjustment on Windows to default window size
+			// This compensates for GTK3's lack of fractional scaling support
+			const int fraction_percent = app_get_windows_fractional_scaling_percent();
+			if (fraction_percent > 0) {
+				int glade_w = 0, glade_h = 0;
+				this->get_default_size(glade_w, glade_h);
+				if (glade_w > 0 && glade_h > 0) {
+					const int scaled_w = static_cast<int>(glade_w * (1.0 + fraction_percent / 100.0));
+					const int scaled_h = static_cast<int>(glade_h * (1.0 + fraction_percent / 100.0));
+					this->set_default_size(scaled_w, scaled_h);
+				}
+			}
+
 			// Connect callbacks
 
 			Gtk::Button* save_as_button = nullptr;