diff --git a/glslview.c b/glslview.c
index b0b5d1b..2444725 100644
--- a/glslview.c
+++ b/glslview.c
@@ -172,17 +172,27 @@ static void handle_input(const char *input) {
 }
 
 static void usage(void) {
-	fprintf(stderr, "Usage: glslview [-t <time>] [-s <speed>] [-0 <param0>] [-1 <param1>] [-2 <param2>] <shader>\n");
+	fprintf(stderr, "Usage: glslview [-w <width>] [-h <height>] [-t <time>] [-s <speed>] [-0 <param0>] [-1 <param1>] [-2 <param2>] <shader>\n");
 	exit(1);
 }
 
 int main(int argc, char *argv[]) {
+	int width = 800, height = 800;
+
 	while (true) {
-		int c = getopt(argc, argv, "t:s:0:1:2:");
+		int c = getopt(argc, argv, "w:h:t:s:0:1:2:");
 		if (c == -1)
 			break;
 
 		switch (c) {
+		case 'w':
+			width = atoi(optarg);
+			break;
+
+		case 'h':
+			height = atoi(optarg);
+			break;
+
 		case 't':
 			current_time = init_time = atof(optarg);
 			break;
@@ -220,7 +230,7 @@ int main(int argc, char *argv[]) {
 	SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8);
 	SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);
 
-	SDL_Window *window = SDL_CreateWindow("glslview", 0, 0, 800, 800, SDL_WINDOW_OPENGL|SDL_WINDOW_RESIZABLE);
+	SDL_Window *window = SDL_CreateWindow("glslview", 0, 0, width, height, SDL_WINDOW_OPENGL|SDL_WINDOW_RESIZABLE);
 	SDL_GLContext ctx = SDL_GL_CreateContext(window);
 
 	filename = argv[optind];
diff --git a/glslwrite.c b/glslwrite.c
index 6673146..5b09c86 100644
--- a/glslwrite.c
+++ b/glslwrite.c
@@ -91,17 +91,27 @@ static void savePNG(int width, int height, const char *output_dir) {
 }
 
 static void usage(void) {
-	fprintf(stderr, "Usage: glslwrite [-s <step>] [-f <frames>] [-0 <param0>] [-1 <param1>] [-2 <param2>] <shader>\n");
+	fprintf(stderr, "Usage: glslwrite [-w <width>] [-h <height>] [-s <step>] [-f <frames>] [-0 <param0>] [-1 <param1>] [-2 <param2>] <shader>\n");
 	exit(1);
 }
 
 int main(int argc, char *argv[]) {
+	int width = 800, height = 800;
+
 	while (true) {
-		int c = getopt(argc, argv, "s:f:0:1:2:");
+		int c = getopt(argc, argv, "w:h:s:f:0:1:2:");
 		if (c == -1)
 			break;
 
 		switch (c) {
+		case 'w':
+			width = atoi(optarg);
+			break;
+
+		case 'h':
+			height = atoi(optarg);
+			break;
+
 		case 's':
 			step = atof(optarg);
 			break;
@@ -138,7 +148,7 @@ int main(int argc, char *argv[]) {
 	SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8);
 	SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);
 
-	SDL_Window *window = SDL_CreateWindow("glslwrite", 0, 0, 800, 800, SDL_WINDOW_OPENGL|SDL_WINDOW_RESIZABLE);
+	SDL_Window *window = SDL_CreateWindow("glslwrite", 0, 0, width, height, SDL_WINDOW_OPENGL|SDL_WINDOW_RESIZABLE);
 	SDL_GLContext ctx = SDL_GL_CreateContext(window);
 
 	filename = argv[optind];