diff --git a/core/pdf_exporter.py b/core/pdf_exporter.py
index c1461c9..eeaa729 100644
--- a/core/pdf_exporter.py
+++ b/core/pdf_exporter.py
@@ -375,6 +375,8 @@ def export_wireframe_to_pdf(
 
     w_geom = max_x - min_x
     h_geom = max_y - min_y
+    center_x = (min_x + max_x) / 2.0
+    center_y = (min_y + max_y) / 2.0
 
     L = max(w_geom, h_geom)
     if L > 1e-6:
@@ -387,10 +389,17 @@ def export_wireframe_to_pdf(
     minor_step = main_step / 10.0
 
     if len(edges_to_draw) > 0 or len(edges_2d) > 0:
-        grid_min_x = math.floor(min_x / main_step) * main_step
-        grid_max_x = math.ceil(max_x / main_step) * main_step
-        grid_min_y = math.floor(min_y / main_step) * main_step
-        grid_max_y = math.ceil(max_y / main_step) * main_step
+        half_span_x = math.ceil(max(abs(max_x - center_x), abs(min_x - center_x)) / main_step) * main_step
+        half_span_y = math.ceil(max(abs(max_y - center_y), abs(min_y - center_y)) / main_step) * main_step
+        if half_span_x == 0:
+            half_span_x = main_step
+        if half_span_y == 0:
+            half_span_y = main_step
+
+        grid_min_x = math.floor((center_x - half_span_x) / main_step) * main_step
+        grid_max_x = math.ceil((center_x + half_span_x) / main_step) * main_step
+        grid_min_y = math.floor((center_y - half_span_y) / main_step) * main_step
+        grid_max_y = math.ceil((center_y + half_span_y) / main_step) * main_step
 
         if grid_min_x == grid_max_x:
             grid_max_x += main_step
@@ -403,8 +412,11 @@ def export_wireframe_to_pdf(
     w_grid_mm = grid_max_x - grid_min_x
     h_grid_mm = grid_max_y - grid_min_y
 
-    w_total_mm = w_grid_mm + 2.0 * margin_mm
-    h_total_mm = h_grid_mm + 2.0 * margin_mm
+    # Paper margin: user margin_mm + 2x smaller grid step in all directions
+    total_margin_mm = margin_mm + 2.0 * minor_step
+
+    w_total_mm = w_grid_mm + 2.0 * total_margin_mm
+    h_total_mm = h_grid_mm + 2.0 * total_margin_mm
 
     page_w_pt = w_total_mm * MM_TO_PT
     page_h_pt = h_total_mm * MM_TO_PT
@@ -412,8 +424,8 @@ def export_wireframe_to_pdf(
     line_width_pt = line_width_mm * MM_TO_PT
 
     def to_pdf_pt(pt_mm):
-        x_pt = (pt_mm[:, 0] - grid_min_x + margin_mm) * MM_TO_PT
-        y_pt = (pt_mm[:, 1] - grid_min_y + margin_mm) * MM_TO_PT
+        x_pt = (pt_mm[:, 0] - grid_min_x + total_margin_mm) * MM_TO_PT
+        y_pt = (pt_mm[:, 1] - grid_min_y + total_margin_mm) * MM_TO_PT
         return np.column_stack([x_pt, y_pt])
 
     max_grid_steps = 2000
diff --git a/tests/test_pdf_exporter.py b/tests/test_pdf_exporter.py
index 99192b8..9a96d17 100644
--- a/tests/test_pdf_exporter.py
+++ b/tests/test_pdf_exporter.py
@@ -143,8 +143,10 @@ class TestPdfExporter(unittest.TestCase):
             with open(pdf_path, "rb") as f:
                 content = f.read()
 
-            expected_w = (100.0 + 2 * margin_mm) * MM_TO_PT
-            expected_h = (100.0 + 2 * margin_mm) * MM_TO_PT
+            minor_step = 1.0  # main_step 10.0 / 10
+            total_margin_mm = margin_mm + 2.0 * minor_step
+            expected_w = (100.0 + 2 * total_margin_mm) * MM_TO_PT
+            expected_h = (100.0 + 2 * total_margin_mm) * MM_TO_PT
             mediabox_str = f"/MediaBox [0 0 {expected_w:.2f} {expected_h:.2f}]".encode("utf-8")
 
             self.assertTrue(content.startswith(b"%PDF-1.4"))