diff --git a/src/obidmscolumn.c b/src/obidmscolumn.c
index 64f5ec5..e4f7055 100644
--- a/src/obidmscolumn.c
+++ b/src/obidmscolumn.c
@@ -547,11 +547,11 @@ size_t obi_get_platform_header_size()
 }
 
 
-OBIDMS_column_p obi_create_column(OBIDMS_p dms,
+OBIDMS_column_p obi_create_column(OBIDMS_p    dms,
 		                          const char* column_name,
-								  OBIType_t data_type,
-								  index_t nb_lines,
-								  index_t nb_elements_per_line,
+								  OBIType_t   data_type,
+								  index_t     nb_lines,
+								  index_t     nb_elements_per_line,
 								  const char* elements_names,
 								  const char* array_name)
 {
@@ -733,6 +733,7 @@ OBIDMS_column_p obi_create_column(OBIDMS_p dms,
 	header 				  		 = new_column->header;
 	header->little_endian 		 = obi_is_little_endian();
 	header->header_size   		 = header_size;
+	header->data_size			 = data_size;
 	header->line_count   	 	 = nb_lines;
 	header->lines_used    		 = 0;
 	header->nb_elements_per_line = nb_elements_per_line;
@@ -781,7 +782,6 @@ OBIDMS_column_p obi_open_column(OBIDMS_p dms,
 	char* 						column_file_name;
 	int 						column_file_descriptor;
 	size_t 						header_size;
-	size_t 						data_size;
 
 	column = NULL;
 
@@ -856,12 +856,9 @@ OBIDMS_column_p obi_open_column(OBIDMS_p dms,
 		return NULL;
 	}
 
-	// Compute data size from the informations in the header
-	data_size = obi_array_sizeof((column->header)->data_type, (column->header)->line_count, (column->header)->nb_elements_per_line);
-
 	// Map the data
 	column->data   			 = mmap(NULL,
-			                 	 	data_size,
+			                 	 	(column->header)->data_size,
 			                 	 	PROT_READ,
 									MAP_PRIVATE,
 			                 	 	column_file_descriptor,
@@ -901,16 +898,15 @@ OBIDMS_column_p obi_open_column(OBIDMS_p dms,
 }
 
 
-OBIDMS_column_p obi_clone_column(OBIDMS_p dms,
-								 const char* column_name,
+OBIDMS_column_p obi_clone_column(OBIDMS_p     dms,
+								 const char*  column_name,
 								 obiversion_t version_number,
-								 bool clone_data)
+								 bool 		  clone_data)
 {
 	OBIDMS_column_p   column_to_clone;
 	OBIDMS_column_p   new_column;
 	index_t 		  nb_lines;
 	index_t			  nb_elements_per_line;
-	size_t			  data_size;
 	OBIType_t		  data_type;
 
 	column_to_clone = obi_open_column(dms, column_name, version_number);
@@ -953,8 +949,7 @@ OBIDMS_column_p obi_clone_column(OBIDMS_p dms,
 
 	if (clone_data)
 	{
-		data_size = obi_array_sizeof(data_type, nb_lines, nb_elements_per_line);
-		memcpy(new_column->data, column_to_clone->data, data_size);
+		memcpy(new_column->data, column_to_clone->data, (column_to_clone->header)->data_size);
 		(new_column->header)->lines_used = (column_to_clone->header)->lines_used;
 	}
 
@@ -971,11 +966,8 @@ OBIDMS_column_p obi_clone_column(OBIDMS_p dms,
 
 int obi_close_column(OBIDMS_column_p column)
 {
-	size_t data_size;
-
 	// Munmap data
-	data_size = obi_array_sizeof((column->header)->data_type, (column->header)->line_count, (column->header)->nb_elements_per_line);
-	if (munmap(column->data, data_size) < 0)
+	if (munmap(column->data, (column->header)->data_size) < 0)
 	{
 		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		obidebug(1, "\nError munmapping column data");
@@ -1035,8 +1027,7 @@ int obi_truncate_column_to_lines_used(OBIDMS_column_p column)	// TODO is it nece
 	free(column_file_name);
 
 	// Unmap the data before truncating the file
-	data_size = obi_array_sizeof((column->header)->data_type, (column->header)->line_count, (column->header)->nb_elements_per_line);
-	if (munmap(column->data, data_size) < 0)
+	if (munmap(column->data, (column->header)->data_size) < 0)
 	{
 		obi_set_errno(OBICOL_UNKNOWN_ERROR);
 		obidebug(1, "\nError munmapping the data of a column before truncating");
@@ -1072,8 +1063,9 @@ int obi_truncate_column_to_lines_used(OBIDMS_column_p column)	// TODO is it nece
 		return -1;
 	}
 
-	// Set line_count to the new line count
+	// Set new line_count and new data size
 	(column->header)->line_count = new_line_count;
+	(column->header)->data_size = data_size;
 
 	close(column_file_descriptor);
 
@@ -1123,7 +1115,7 @@ int obi_enlarge_column(OBIDMS_column_p column)
 		close(column_file_descriptor);
 		return -1;
 	}
-	old_data_size = obi_array_sizeof((column->header)->data_type, old_line_count, (column->header)->nb_elements_per_line);
+	old_data_size = (column->header)->data_size;
 	new_data_size = old_data_size * COLUMN_GROWTH_FACTOR;
 	header_size = (column->header)->header_size;
 	file_size = header_size + new_data_size;
@@ -1185,8 +1177,9 @@ int obi_enlarge_column(OBIDMS_column_p column)
 		}
 	}
 
-	// Set new line count
+	// Set new line count and new data size
 	(column->header)->line_count = new_line_count;
+	(column->header)->data_size = new_data_size;
 
 	// Initialize new data lines to NA
 	obi_ini_to_NA_values(column, old_line_count, new_line_count - old_line_count);
diff --git a/src/obidmscolumn.h b/src/obidmscolumn.h
index 587c8d5..399a171 100644
--- a/src/obidmscolumn.h
+++ b/src/obidmscolumn.h
@@ -55,6 +55,8 @@ typedef struct OBIDMS_column_header {
 											     	 	 	 */
 	size_t			header_size;		   				    /**< Size of the header in bytes.
 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 */
+	size_t			data_size;			   				    /**< Size of the data in bytes.
+	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 */
 	index_t			line_count;							    /**< Number of lines of data allocated.
 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 */
 	index_t			lines_used;							    /**< Number of lines of data used.