If you want to know which Magento version used by website the you can check it by following ways.
- Using URL
www.yourdomin.com/magento_version
- Using Command
php ./bin/magento –version
- Using composer
In composer.json file “version” property
- Magento Backend
Magento Admin panel right bottom section(in footer)
I hope this blog is useful for you. thank you!
