diff --git modules/book/book.admin.inc modules/book/book.admin.inc
index 819765d..e8464ee 100644
--- modules/book/book.admin.inc
+++ modules/book/book.admin.inc
@@ -176,6 +176,8 @@ function _book_admin_table($node, &$form) {
  * @see book_admin_edit()
  */
 function _book_admin_table_tree($tree, &$form) {
+  $delta = book_weight_delta_calculate($tree);
+
   foreach ($tree as $data) {
     $form['book-admin-' . $data['link']['nid']] = array(
       '#item' => $data['link'],
@@ -191,7 +193,7 @@ function _book_admin_table_tree($tree, &$form) {
       'weight' => array(
         '#type' => 'weight',
         '#default_value' => $data['link']['weight'],
-        '#delta' => 15,
+        '#delta' => $delta,
       ),
       'plid' => array(
         '#type' => 'textfield',
diff --git modules/book/book.module modules/book/book.module
index 3552998..ac5ad03 100644
--- modules/book/book.module
+++ modules/book/book.module
@@ -504,11 +504,15 @@ function _book_add_form_elements(&$form, &$form_state, $node) {
 
   $form['book']['plid'] = _book_parent_select($node->book);
 
+  $tree = book_menu_subtree_data(menu_link_load($node->book['plid']));
+  $tree = array_shift($tree);  // Do not include the book item itself.
+  $delta = book_weight_delta_calculate($tree['below']);
+
   $form['book']['weight'] = array(
     '#type' => 'weight',
     '#title' => t('Weight'),
     '#default_value' => $node->book['weight'],
-    '#delta' => 15,
+    '#delta' => $delta,
     '#weight' => 5,
     '#description' => t('Pages at a given level are ordered first by weight and then by title.'),
   );
@@ -554,6 +558,26 @@ function _book_add_form_elements(&$form, &$form_state, $node) {
 }
 
 /**
+ * Provides the delta required (minimum 15) for weighting nodes in a book. 
+ *
+ * Takes a modified book subtree, such as $tree['below'] after getting $tree:
+ * $tree = array_shift(book_menu_subtree_data($node->book));
+ */
+function book_weight_delta_calculate($tree) {
+  // The delta must be big enough to give each node a distinct value.
+  $count = intval(count($tree) / 2) + 1;
+  // The delta must be as large as any existing delta.
+  $high = 0;
+  if ($tree) {
+    foreach ($tree as $value) {
+      $weight = abs($value['link']['weight']);
+      if ($weight > $high)  $high = $weight;
+    }
+  }
+  return max(15, $count, $high + 1);
+}
+
+/**
  * Common helper function to handles additions and updates to the book outline.
  *
  * Performs all additions and updates to the book outline through node addition,