diff --git a/system/Files/File.php b/system/Files/File.php
index 15b53262e9c2..67a1c3ce37f1 100644
--- a/system/Files/File.php
+++ b/system/Files/File.php
@@ -72,14 +72,18 @@ public function getSize()
 
     /**
      * Retrieve the file size by unit.
+     * Supports the metric units "kb" and "mb"
+     * and the IEC units "kib" and "mib".
      *
      * @return false|int|string
      */
     public function getSizeByUnit(string $unit = 'b')
     {
         return match (strtolower($unit)) {
-            'kb'    => number_format($this->getSize() / 1024, 3),
-            'mb'    => number_format(($this->getSize() / 1024) / 1024, 3),
+            'kb'    => number_format($this->getSize() / 1000, 3),
+            'kib'   => number_format($this->getSize() / 1024, 3),
+            'mb'    => number_format(($this->getSize() / 1000) / 1000, 3),
+            'mib'   => number_format(($this->getSize() / 1024) / 1024, 3),
             default => $this->getSize(),
         };
     }
diff --git a/tests/system/Files/FileTest.php b/tests/system/Files/FileTest.php
index 800a1ac278f1..862ffada7187 100644
--- a/tests/system/Files/FileTest.php
+++ b/tests/system/Files/FileTest.php
@@ -92,17 +92,31 @@ public function testCanAccessSplFileInfoMethods(): void
         $this->assertSame('file', $file->getType());
     }
 
-    public function testGetSizeReturnsKB(): void
+    public function testGetSizeReturnsKiB(): void
     {
         $file = new File(SYSTEMPATH . 'Common.php');
         $size = number_format(filesize(SYSTEMPATH . 'Common.php') / 1024, 3);
+        $this->assertSame($size, $file->getSizeByUnit('kib'));
+    }
+
+    public function testGetSizeReturnsKB(): void
+    {
+        $file = new File(SYSTEMPATH . 'Common.php');
+        $size = number_format(filesize(SYSTEMPATH . 'Common.php') / 1000, 3);
         $this->assertSame($size, $file->getSizeByUnit('kb'));
     }
 
-    public function testGetSizeReturnsMB(): void
+    public function testGetSizeReturnsMiB(): void
     {
         $file = new File(SYSTEMPATH . 'Common.php');
         $size = number_format(filesize(SYSTEMPATH . 'Common.php') / 1024 / 1024, 3);
+        $this->assertSame($size, $file->getSizeByUnit('mib'));
+    }
+
+    public function testGetSizeReturnsMB(): void
+    {
+        $file = new File(SYSTEMPATH . 'Common.php');
+        $size = number_format(filesize(SYSTEMPATH . 'Common.php') / 1000 / 1000, 3);
         $this->assertSame($size, $file->getSizeByUnit('mb'));
     }