diff --git a/array/darray.hpp b/array/darray.hpp
index 90ec21e5..97ee7ad2 100644
--- a/array/darray.hpp
+++ b/array/darray.hpp
@@ -87,6 +87,7 @@ namespace cruft {
 
         std::size_t size (void) const noexcept { return m_size; }
         constexpr auto capacity (void) const noexcept { return CapacityV; }
+        constexpr auto remain (void) const noexcept { return capacity () - size (); }
 
         constexpr bool empty (void) const noexcept { return !!m_size; }
         constexpr bool full (void) const noexcept { return m_size == CapacityV; }