diff --git a/matrix.hpp b/matrix.hpp
index 20356f5..da56d3d 100644
--- a/matrix.hpp
+++ b/matrix.hpp
@@ -1,6 +1,7 @@
 #ifndef MATRIX_H_
 #define MATRIX_H_
 
+#include <cstddef>
 #include <cstdint>
 #include <fstream>
 #include <iostream>
@@ -68,6 +69,8 @@ template <class T> struct Matrix {
     constexpr XXH32_hash_t HASH_SEED = 42;
     return XXH32(this->data.data(), mem.size(), HASH_SEED);
   }
+
+  std::size_t bytes() const { return this->mem.size() * sizeof(T); }
 };
 
 template <class T> std::ostream &operator<<(std::ostream &os, Matrix<T> &mat) {