Index: branches/5.2.x/core/kernel/application.php
===================================================================
--- branches/5.2.x/core/kernel/application.php
+++ branches/5.2.x/core/kernel/application.php
@@ -306,6 +306,8 @@
 		$this->cacheManager = $this->makeClass('kCacheManager');
 		$this->cacheManager->InitCache();
 
+		define('MAX_UPLOAD_SIZE', $this->getMaxUploadSize());
+
 		if ( defined('DEBUG_MODE') && $this->isDebugMode() ) {
 			$this->Debugger->appendTimestamp('Before UnitConfigReader');
 		}
@@ -394,6 +396,36 @@
 	}
 
 	/**
+	 * Calculates maximal upload file size
+	 *
+	 * @return integer
+	 */
+	protected function getMaxUploadSize()
+	{
+		$cache_key = 'max_upload_size';
+		$max_upload_size = $this->getCache($cache_key);
+
+		if ( $max_upload_size === false ) {
+			$max_upload_size = kUtil::parseIniSize(ini_get('upload_max_filesize'));
+			$post_max_size = ini_get('post_max_size');
+
+			if ( $post_max_size !== '0' ) {
+				$max_upload_size = min($max_upload_size, kUtil::parseIniSize($post_max_size));
+			}
+
+			$memory_limit = ini_get('memory_limit');
+
+			if ( $memory_limit !== '-1' ) {
+				$max_upload_size = min($max_upload_size, kUtil::parseIniSize($memory_limit));
+			}
+
+			$this->setCache($cache_key, $max_upload_size);
+		}
+
+		return $max_upload_size;
+	}
+
+	/**
 	 * Performs initialization of manager classes, that can be overridden from unit configs
 	 *
 	 * @return void
Index: branches/5.2.x/core/kernel/globals.php
===================================================================
--- branches/5.2.x/core/kernel/globals.php
+++ branches/5.2.x/core/kernel/globals.php
@@ -997,6 +997,33 @@
 		}
 	}
 
+	/**
+	 * Parse ini size
+	 *
+	 * @param string $size Size.
+	 *
+	 * @return integer
+	 */
+	public static function parseIniSize($size)
+	{
+		$result = (int)$size;
+		$size = strtolower($size);
+
+		if ( strpos($size, 'k') ) {
+			return $result * 1024;
+		}
+
+		if ( strpos($size, 'm') ) {
+			return $result * 1024 * 1024;
+		}
+
+		if ( strpos($size, 'g') ) {
+			return $result * 1024 * 1024 * 1024;
+		}
+
+		return $result;
+	}
+
 }
 
 /**
Index: branches/5.2.x/core/kernel/startup.php
===================================================================
--- branches/5.2.x/core/kernel/startup.php
+++ branches/5.2.x/core/kernel/startup.php
@@ -114,7 +114,6 @@
 
 	define('IMAGES_PATH', WRITEBALE_BASE . '/images/');
 	define('IMAGES_PENDING_PATH', IMAGES_PATH . 'pending/');
-	define('MAX_UPLOAD_SIZE', min(ini_get('upload_max_filesize'), ini_get('post_max_size'))*1024*1024);
 
 	define('EDITOR_PATH', $vars['EditorPath']);