diff --git a/arena.h b/arena.h
index 01a910a..be6b766 100644
--- a/arena.h
+++ b/arena.h
@@ -1,4 +1,4 @@
-// arena.h - v1.2.0 - MIT License
+// arena.h - v1.2.1 - MIT License
 // single header library for region-based memory management.
 //
 // [License and changelog]
@@ -25,6 +25,11 @@
 //
 //         This macro defines the default capacity for arena regions.
 //
+//     #define ARENA_REGION_GROWTH_FACTOR new_region_growth_factor (1.5f)
+//
+//         This macro defines the growth factor of the capacity for every
+//         subsequent region in all arenas.
+//
 //     #define ARENA_ALIGNMENT alignment (8)
 //
 //         This macro defines the memory alignment used for allocations.
@@ -153,6 +158,10 @@ int main(void)
 #    define ARENA_REGION_CAPACITY (8*1024)
 #endif // ARENA_REGION_CAPACITY
 
+#ifndef ARENA_REGION_GROWTH_FACTOR
+#    define ARENA_REGION_GROWTH_FACTOR 1.5f
+#endif // ARENA_REGION_GROWTH_FACTOR
+
 #ifndef ARENA_ALIGNMENT
 #    define ARENA_ALIGNMENT alignof(max_align_t)
 #endif // ARENA_ALIGNMENT
@@ -300,8 +309,16 @@ void *arena_alloc(Arena *a, size_t size)
         return NULL;
     }
 
+    // Get the next region capacity multiplied by the growth factor
     size_t region_capacity = (a->region_capacity == 0
                                 ? ARENA_REGION_CAPACITY : a->region_capacity);
+    if (a->tail != NULL) {
+        region_capacity = a->tail->capacity * ARENA_REGION_GROWTH_FACTOR;
+        // Edge case for small growth factors
+        if (region_capacity <= a->tail->capacity) {
+            region_capacity = a->tail->capacity + 1;
+        }
+    }
 
     // Calculate and check region allocation size
     size_t alloc_size = (size > region_capacity ? size : region_capacity);
@@ -491,6 +508,8 @@ size_t arena__align(size_t n)
 /*
  * Revision history:
  *
+ *     1.2.1 (2026-04-08) Region growth factor handling with new
+ *                        ARENA_REGION_GROWTH_FACTOR macro
  *     1.2.0 (2026-04-08) New functions: arena_sprintf(), arena_snapshot(),
  *                        arena_rewind() and arena_trim()
  *     1.1.3 (2026-01-14) Align Arena_Region data flexible array member
diff --git a/test.c b/test.c
index b2c0f1f..f9a8849 100644
--- a/test.c
+++ b/test.c
@@ -9,6 +9,7 @@
 #endif // DEBUG
 
 #define ARENA_IMPLEMENTATION
+#define ARENA_REGION_GROWTH_FACTOR 2
 #include "arena.h"
 
 void arena_print(Arena arena)
@@ -50,8 +51,14 @@ int main(void)
     arena_print(a);
 
     char *str = arena_sprintf(&a, "Formatted string %x", 0xCAFE);
+
+    for (size_t i = 0; i < 1000; ++i) {
+        str = arena_sprintf(&a, "Formatted string %d", i);
+    }
+
     printf("%s\n", str);
 
+    arena_print(a);
     arena_free(&a);
     return 0;
 }