diff --git a/photobooth.py b/photobooth.py
index 6f70db2..723ad0c 100755
--- a/photobooth.py
+++ b/photobooth.py
@@ -180,11 +180,26 @@ _PRINT_MARGIN_IN = 0.5
 
 
 def a4_landscape_chars(cpi, lpi):
-    """(cols, rows) of an A4 sheet printed sideways, at the given pitch."""
+    """(cols, rows) to capture/preview for an A4 landscape printout.
+
+    txt2printr.sh prints on a normally-fed (portrait) page and rotates the
+    ascii art 90 degrees in software; the reader turns the finished sheet
+    90 degrees to view it. That second turn cancels the software rotation,
+    so this buffer's own dimensions equal the final visual result - but its
+    width becomes the printed *line count* after rotation, which must fit
+    within one page's line capacity along the long (feed) edge. Height is
+    then derived from the target landscape aspect ratio, corrected for
+    non-square character cells (cells are cpi/lpi times taller than wide),
+    so the final printout keeps true A4 proportions instead of just filling
+    however many character cells happen to fit.
+    """
     long_in = _A4_LONG_MM / _MM_PER_IN
     short_in = _A4_SHORT_MM / _MM_PER_IN
-    cols = max(1, round((long_in - 2 * _PRINT_MARGIN_IN) * cpi))
-    rows = max(1, round((short_in - 2 * _PRINT_MARGIN_IN) * lpi))
+    max_lines = max(1, round((long_in - 2 * _PRINT_MARGIN_IN) * lpi))
+    max_chars = max(1, round((short_in - 2 * _PRINT_MARGIN_IN) * cpi))
+    aspect = (long_in / short_in) * (cpi / lpi)
+    cols = max_lines
+    rows = max(1, min(max_chars, round(cols / aspect)))
     return cols, rows