diff --git a/wp-admin/includes/file.php b/wp-admin/includes/file.php
index ddd2be849a..759b0974bb 100644
--- a/wp-admin/includes/file.php
+++ b/wp-admin/includes/file.php
@@ -2555,3 +2555,41 @@ function wp_opcache_invalidate( $filepath, $force = false ) {
 
 	return false;
 }
+
+/**
+ * Wrapper for PHP filesize with filters and casting the result as an integer.
+ *
+ * @since 6.0.0
+ *
+ * @link https://www.php.net/manual/en/function.filesize.php
+ *
+ * @param string $path Path to the file.
+ * @return int The size of the file in bytes, or 0 in the event of an error.
+ */
+function wp_filesize( $path ) {
+	/**
+	 * Filters the result of wp_filesize before the PHP function is run.
+	 *
+	 * @since 6.0.0
+	 *
+	 * @param null|int $size The unfiltered value. Returning an int from the callback bypasses the filesize call.
+	 * @param string   $path Path to the file.
+	 */
+	$size = apply_filters( 'pre_wp_filesize', null, $path );
+
+	if ( is_int( $size ) ) {
+		return $size;
+	}
+
+	$size = (int) @filesize( $path );
+
+	/**
+	 * Filters the size of the file.
+	 *
+	 * @since 6.0.0
+	 *
+	 * @param int    $size The result of PHP filesize on the file.
+	 * @param string $path Path to the file.
+	 */
+	return (int) apply_filters( 'wp_filesize', $size, $path );
+}
diff --git a/wp-admin/includes/image.php b/wp-admin/includes/image.php
index 627fdfb4b5..2818b3dd5d 100644
--- a/wp-admin/includes/image.php
+++ b/wp-admin/includes/image.php
@@ -210,6 +210,9 @@ function _wp_image_meta_replace_original( $saved_data, $original_file, $image_me
 	// Store the original image file name in image_meta.
 	$image_meta['original_image'] = wp_basename( $original_file );
 
+	// Add image file size.
+	$image_meta['filesize'] = wp_filesize( $new_file );
+
 	return $image_meta;
 }
 
@@ -235,10 +238,11 @@ function wp_create_image_subsizes( $file, $attachment_id ) {
 
 	// Default image meta.
 	$image_meta = array(
-		'width'  => $imagesize[0],
-		'height' => $imagesize[1],
-		'file'   => _wp_relative_upload_path( $file ),
-		'sizes'  => array(),
+		'width'    => $imagesize[0],
+		'height'   => $imagesize[1],
+		'file'     => _wp_relative_upload_path( $file ),
+		'filesize' => wp_filesize( $file ),
+		'sizes'    => array(),
 	);
 
 	// Fetch additional metadata from EXIF/IPTC.
@@ -629,6 +633,11 @@ function wp_generate_attachment_metadata( $attachment_id, $file ) {
 	// Remove the blob of binary data from the array.
 	unset( $metadata['image']['data'] );
 
+	// Capture file size for cases where it has not been captured yet, such as PDFs.
+	if ( ! isset( $metadata['filesize'] ) && file_exists( $file ) ) {
+		$metadata['filesize'] = wp_filesize( $file );
+	}
+
 	/**
 	 * Filters the generated attachment meta data.
 	 *
diff --git a/wp-admin/includes/media.php b/wp-admin/includes/media.php
index d9dcbd5d7d..093ee69360 100644
--- a/wp-admin/includes/media.php
+++ b/wp-admin/includes/media.php
@@ -3378,7 +3378,7 @@ function attachment_submitbox_metadata() {
 	if ( isset( $meta['filesize'] ) ) {
 		$file_size = $meta['filesize'];
 	} elseif ( file_exists( $file ) ) {
-		$file_size = filesize( $file );
+		$file_size = wp_filesize( $file );
 	}
 
 	if ( ! empty( $file_size ) ) {
diff --git a/wp-includes/class-wp-image-editor-gd.php b/wp-includes/class-wp-image-editor-gd.php
index f32e2b4202..f745bcf9f8 100644
--- a/wp-includes/class-wp-image-editor-gd.php
+++ b/wp-includes/class-wp-image-editor-gd.php
@@ -497,6 +497,7 @@ class WP_Image_Editor_GD extends WP_Image_Editor {
 			'width'     => $this->size['width'],
 			'height'    => $this->size['height'],
 			'mime-type' => $mime_type,
+			'filesize'  => wp_filesize( $filename ),
 		);
 	}
 
diff --git a/wp-includes/class-wp-image-editor-imagick.php b/wp-includes/class-wp-image-editor-imagick.php
index d898db553a..fea2e5e4ef 100644
--- a/wp-includes/class-wp-image-editor-imagick.php
+++ b/wp-includes/class-wp-image-editor-imagick.php
@@ -729,6 +729,7 @@ class WP_Image_Editor_Imagick extends WP_Image_Editor {
 			'width'     => $this->size['width'],
 			'height'    => $this->size['height'],
 			'mime-type' => $mime_type,
+			'filesize'  => wp_filesize( $filename ),
 		);
 	}
 
diff --git a/wp-includes/media.php b/wp-includes/media.php
index 5ab3cd1913..b3204c2799 100644
--- a/wp-includes/media.php
+++ b/wp-includes/media.php
@@ -4046,7 +4046,7 @@ function wp_prepare_attachment_for_js( $attachment ) {
 	if ( isset( $meta['filesize'] ) ) {
 		$bytes = $meta['filesize'];
 	} elseif ( file_exists( $attached_file ) ) {
-		$bytes = filesize( $attached_file );
+		$bytes = wp_filesize( $attached_file );
 	} else {
 		$bytes = '';
 	}
diff --git a/wp-includes/post.php b/wp-includes/post.php
index 10dddf859b..7cf8204e05 100644
--- a/wp-includes/post.php
+++ b/wp-includes/post.php
@@ -6538,6 +6538,7 @@ function wp_delete_attachment_files( $post_id, $meta, $backup_sizes, $file ) {
  *     @type array  $sizes      Keys are size slugs, each value is an array containing
  *                              'file', 'width', 'height', and 'mime-type'.
  *     @type array  $image_meta Image metadata.
+ *     @type int    $filesize   File size of the attachment.
  * }
  */
 function wp_get_attachment_metadata( $attachment_id = 0, $unfiltered = false ) {
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 7705c0ca83..87e1cd24f8 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.0-alpha-52836';
+$wp_version = '6.0-alpha-52837';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.