diff --git a/src/app.c b/src/app.c
index 6ac3aef..b355fdd 100644
--- a/src/app.c
+++ b/src/app.c
@@ -137,6 +137,21 @@ static void tune_relative(App *app, int delta) {
     player_tune(&app->player, next_index);
 }
 
+static void toggle_fullscreen(App *app) {
+    Uint32 flags;
+
+    if (!app || !app->window) {
+        return;
+    }
+
+    flags = app->is_fullscreen ? 0 : SDL_WINDOW_FULLSCREEN_DESKTOP;
+    if (SDL_SetWindowFullscreen(app->window, flags) == 0) {
+        app->is_fullscreen = !app->is_fullscreen;
+    } else {
+        fprintf(stderr, "Fullscreen toggle failed: %s\n", SDL_GetError());
+    }
+}
+
 static void handle_event(App *app, const SDL_Event *event) {
     if (event->type == SDL_QUIT) {
         app->running = 0;
@@ -158,6 +173,9 @@ static void handle_event(App *app, const SDL_Event *event) {
         case SDLK_TAB:
             app->mode = app->mode == MODE_FULLSCREEN ? MODE_GUIDE : MODE_FULLSCREEN;
             break;
+        case SDLK_f:
+            toggle_fullscreen(app);
+            break;
         case SDLK_UP:
             tune_relative(app, -1);
             break;
@@ -243,6 +261,8 @@ void app_run(App *app) {
 
     while (app->running) {
         int in_blackout;
+        int output_width = WINDOW_WIDTH;
+        int output_height = WINDOW_HEIGHT;
         Uint64 now_ticks;
         time_t now_wall;
 
@@ -255,6 +275,11 @@ void app_run(App *app) {
             break;
         }
 
+        if (SDL_GetRendererOutputSize(app->renderer, &output_width, &output_height) != 0) {
+            output_width = WINDOW_WIDTH;
+            output_height = WINDOW_HEIGHT;
+        }
+
         in_blackout = player_is_in_blackout(&app->player);
         now_ticks = SDL_GetTicks64();
         now_wall = time(NULL);
@@ -266,7 +291,7 @@ void app_run(App *app) {
         app->last_blackout_state = in_blackout;
 
         if (app->channels.count == 0) {
-            ui_render_no_media(app->renderer, &app->ui_cache);
+            ui_render_no_media(app->renderer, &app->ui_cache, output_width, output_height);
         } else if (app->mode == MODE_GUIDE) {
             if (!in_blackout) {
                 player_resume_audio(&app->player);
@@ -275,6 +300,8 @@ void app_run(App *app) {
                             in_blackout ? NULL : app->video_texture,
                             app->texture_width,
                             app->texture_height,
+                            output_width,
+                            output_height,
                             &app->fonts,
                             &app->ui_cache,
                             &app->channels,
@@ -289,7 +316,9 @@ void app_run(App *app) {
             ui_render_fullscreen(app->renderer,
                                  in_blackout ? NULL : app->video_texture,
                                  app->texture_width,
-                                 app->texture_height);
+                                 app->texture_height,
+                                 output_width,
+                                 output_height);
         }
 
         SDL_RenderPresent(app->renderer);
diff --git a/src/app.h b/src/app.h
index 1a70c95..9f0e269 100644
--- a/src/app.h
+++ b/src/app.h
@@ -16,6 +16,7 @@ typedef struct App {
     int texture_height;
     AppMode mode;
     int running;
+    int is_fullscreen;
     int startup_handoff_active;
     int last_blackout_state;
     Uint32 startup_handoff_until;
diff --git a/src/app.o b/src/app.o
index b89b500..c3becbd 100644
Binary files a/src/app.o and b/src/app.o differ
diff --git a/src/ui.c b/src/ui.c
index d9d9bc3..ea9d2de 100644
--- a/src/ui.c
+++ b/src/ui.c
@@ -481,16 +481,21 @@ static void draw_scanline_overlay(SDL_Renderer *renderer, int width, int height)
     SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_NONE);
 }
 
-void ui_render_no_media(SDL_Renderer *renderer, const UiCache *cache) {
-    SDL_Rect full = {0, 0, WINDOW_WIDTH, WINDOW_HEIGHT};
+void ui_render_no_media(SDL_Renderer *renderer, const UiCache *cache, int window_width, int window_height) {
+    SDL_Rect full = {0, 0, window_width, window_height};
     fill_rect(renderer, &full, COLOR_NAVY_DARK);
     draw_cached_text(renderer, &cache->no_media_title, 58, 80);
     draw_cached_text(renderer, &cache->no_media_body, 58, 136);
     draw_cached_text(renderer, &cache->no_media_hint, 58, 176);
 }
 
-void ui_render_fullscreen(SDL_Renderer *renderer, SDL_Texture *video_texture, int texture_width, int texture_height) {
-    SDL_Rect window = {0, 0, WINDOW_WIDTH, WINDOW_HEIGHT};
+void ui_render_fullscreen(SDL_Renderer *renderer,
+                          SDL_Texture *video_texture,
+                          int texture_width,
+                          int texture_height,
+                          int window_width,
+                          int window_height) {
+    SDL_Rect window = {0, 0, window_width, window_height};
     fill_rect(renderer, &window, COLOR_BLACK);
     draw_video(renderer, video_texture, texture_width, texture_height, window);
 }
@@ -499,6 +504,8 @@ void ui_render_guide(SDL_Renderer *renderer,
                      SDL_Texture *video_texture,
                      int texture_width,
                      int texture_height,
+                     int window_width,
+                     int window_height,
                      const UiFonts *fonts,
                      UiCache *cache,
                      const ChannelList *channels,
@@ -506,14 +513,18 @@ void ui_render_guide(SDL_Renderer *renderer,
                      Uint64 app_start_ticks,
                      Uint64 now_ticks,
                      time_t now_wall) {
-    SDL_Rect full = {0, 0, WINDOW_WIDTH, WINDOW_HEIGHT};
-    SDL_Rect info_panel = {0, 0, GUIDE_INFO_WIDTH, GUIDE_INFO_HEIGHT};
-    SDL_Rect preview = {WINDOW_WIDTH - GUIDE_PREVIEW_WIDTH, 0, GUIDE_PREVIEW_WIDTH, GUIDE_PREVIEW_HEIGHT};
-    SDL_Rect status_bar = {GUIDE_INFO_WIDTH, 0, WINDOW_WIDTH - GUIDE_INFO_WIDTH, GUIDE_STATUS_HEIGHT};
-    SDL_Rect header_row = {0, GUIDE_GRID_TOP - GUIDE_STATUS_HEIGHT, WINDOW_WIDTH, GUIDE_STATUS_HEIGHT};
-    SDL_Rect grid = {0, GUIDE_GRID_TOP, WINDOW_WIDTH, WINDOW_HEIGHT - GUIDE_GRID_TOP - GUIDE_FOOTER_HEIGHT};
+    double scale_x = (double) window_width / WINDOW_WIDTH;
+    double scale_y = (double) window_height / WINDOW_HEIGHT;
+    int guide_x_start = (int) (GUIDE_X_START * scale_x);
+    int sidebar_width = (int) (GUIDE_SIDEBAR_WIDTH * scale_x);
+    SDL_Rect full = {0, 0, window_width, window_height};
+    SDL_Rect info_panel = {0, 0, (int) (GUIDE_INFO_WIDTH * scale_x), (int) (GUIDE_INFO_HEIGHT * scale_y)};
+    SDL_Rect preview = {window_width - (int) (GUIDE_PREVIEW_WIDTH * scale_x), 0, (int) (GUIDE_PREVIEW_WIDTH * scale_x), (int) (GUIDE_PREVIEW_HEIGHT * scale_y)};
+    SDL_Rect status_bar = {info_panel.w, 0, window_width - info_panel.w, (int) (GUIDE_STATUS_HEIGHT * scale_y)};
+    SDL_Rect header_row = {0, (int) ((GUIDE_GRID_TOP - GUIDE_STATUS_HEIGHT) * scale_y), window_width, (int) (GUIDE_STATUS_HEIGHT * scale_y)};
+    SDL_Rect grid = {0, (int) (GUIDE_GRID_TOP * scale_y), window_width, window_height - (int) (GUIDE_GRID_TOP * scale_y) - (int) (GUIDE_FOOTER_HEIGHT * scale_y)};
     int row_height = grid.h / GUIDE_VISIBLE_ROWS;
-    int timeline_w = WINDOW_WIDTH - GUIDE_X_START - 20;
+    int timeline_w = window_width - guide_x_start - (int) (20 * scale_x);
     int start_index = active_channel - 2;
     const Channel *selected_channel = NULL;
     double pixels_per_minute = timeline_w / 90.0;
@@ -554,9 +565,9 @@ void ui_render_guide(SDL_Renderer *renderer,
 
     for (int row = 0; row < GUIDE_VISIBLE_ROWS; ++row) {
         int channel_index = start_index + row;
-        SDL_Rect row_rect = {0, grid.y + row * row_height, WINDOW_WIDTH, row_height};
-        SDL_Rect sidebar = {0, row_rect.y, GUIDE_SIDEBAR_WIDTH, row_height};
-        SDL_Rect timeline_rect = {GUIDE_X_START, row_rect.y + 6, timeline_w, row_height - 12};
+        SDL_Rect row_rect = {0, grid.y + row * row_height, window_width, row_height};
+        SDL_Rect sidebar = {0, row_rect.y, sidebar_width, row_height};
+        SDL_Rect timeline_rect = {guide_x_start, row_rect.y + (int) (6 * scale_y), timeline_w, row_height - (int) (12 * scale_y)};
         SDL_Rect clip = timeline_rect;
         int is_selected = channel_index == active_channel;
         SDL_Rect inset = {row_rect.x + 4, row_rect.y + 3, row_rect.w - 8, row_rect.h - 6};
@@ -588,9 +599,9 @@ void ui_render_guide(SDL_Renderer *renderer,
             const ProgramEntry *program = channel_resolve_program(channel, app_start_ticks, now_ticks, &program_seek, NULL);
             time_t guide_view_start_time = now_wall - (30 * 60);
             time_t program_start_time = now_wall - (time_t) live_position;
-            int block_x = GUIDE_X_START;
+            int block_x = guide_x_start;
             int block_w = 48;
-            SDL_Rect block = {GUIDE_X_START, timeline_rect.y + 4, 48, timeline_rect.h - 8};
+            SDL_Rect block = {guide_x_start, timeline_rect.y + 4, 48, timeline_rect.h - 8};
             SDL_Rect title_rect = {block.x + 8, block.y + 8, block.w - 16, block.h - 16};
             char title[128];
 
@@ -599,7 +610,7 @@ void ui_render_guide(SDL_Renderer *renderer,
             }
             live_position = channel_live_position_precise(channel, app_start_ticks, now_ticks);
             program_start_time = now_wall - (time_t) program_seek;
-            block_x = GUIDE_X_START + (int) (((double) (program_start_time - guide_view_start_time)) / 60.0 * pixels_per_minute);
+            block_x = guide_x_start + (int) (((double) (program_start_time - guide_view_start_time)) / 60.0 * pixels_per_minute);
             block_w = (int) ((program->duration_seconds / 60.0) * pixels_per_minute);
             block = (SDL_Rect){block_x, timeline_rect.y + 4, SDL_max(block_w, 48), timeline_rect.h - 8};
             title_rect = (SDL_Rect){block.x + 8, block.y + 8, block.w - 16, block.h - 16};
@@ -642,13 +653,13 @@ void ui_render_guide(SDL_Renderer *renderer,
     }
 
     if (selected_channel && active_channel >= 0 && start_index <= active_channel && active_channel < start_index + GUIDE_VISIBLE_ROWS) {
-        SDL_Rect highlight = {0, grid.y + (active_channel - start_index) * row_height, WINDOW_WIDTH, row_height};
+        SDL_Rect highlight = {0, grid.y + (active_channel - start_index) * row_height, window_width, row_height};
         draw_selection_glow(renderer, &highlight);
-        draw_selection_glow(renderer, &(SDL_Rect){GUIDE_X_START, highlight.y + 6, timeline_w, row_height - 12});
+        draw_selection_glow(renderer, &(SDL_Rect){guide_x_start, highlight.y + (int) (6 * scale_y), timeline_w, row_height - (int) (12 * scale_y)});
     }
 
-    draw_footer_legend(renderer, cache, WINDOW_WIDTH, WINDOW_HEIGHT);
-    draw_scanline_overlay(renderer, WINDOW_WIDTH, WINDOW_HEIGHT);
+    draw_footer_legend(renderer, cache, window_width, window_height);
+    draw_scanline_overlay(renderer, window_width, window_height);
 }
 
 int ui_cache_init(UiCache *cache, SDL_Renderer *renderer, const UiFonts *fonts, const ChannelList *channels) {
diff --git a/src/ui.h b/src/ui.h
index 3b3208b..02fc9ac 100644
--- a/src/ui.h
+++ b/src/ui.h
@@ -46,11 +46,18 @@ typedef struct UiCache {
     int channel_count;
 } UiCache;
 
-void ui_render_fullscreen(SDL_Renderer *renderer, SDL_Texture *video_texture, int texture_width, int texture_height);
+void ui_render_fullscreen(SDL_Renderer *renderer,
+                          SDL_Texture *video_texture,
+                          int texture_width,
+                          int texture_height,
+                          int window_width,
+                          int window_height);
 void ui_render_guide(SDL_Renderer *renderer,
                      SDL_Texture *video_texture,
                      int texture_width,
                      int texture_height,
+                     int window_width,
+                     int window_height,
                      const UiFonts *fonts,
                      UiCache *cache,
                      const ChannelList *channels,
@@ -58,7 +65,7 @@ void ui_render_guide(SDL_Renderer *renderer,
                      Uint64 app_start_ticks,
                      Uint64 now_ticks,
                      time_t now_wall);
-void ui_render_no_media(SDL_Renderer *renderer, const UiCache *cache);
+void ui_render_no_media(SDL_Renderer *renderer, const UiCache *cache, int window_width, int window_height);
 int ui_load_fonts(UiFonts *fonts);
 void ui_destroy_fonts(UiFonts *fonts);
 int ui_cache_init(UiCache *cache, SDL_Renderer *renderer, const UiFonts *fonts, const ChannelList *channels);
diff --git a/src/ui.o b/src/ui.o
index b930071..a98777d 100644
Binary files a/src/ui.o and b/src/ui.o differ