Your cockatiel looks to be quite young, so it can be very difficult to visually determine gender if that is the case. Once a cockatiel has gone through it's first moult to adult plumage it is MUCH easier, and this generally takes place around the age of 8 months or so. A female cockatiel will retain the rippled colour on the underside of the tail feathers, much as your cockatiel currently has, into adulthood. A male will lose that colouring, and the underside of the tail feathers will take on a solid colour. Until that time, your best bet is to have it DNA tested by a certified avian vet to determine the gender.
2 umbrella Cockatoos One male named Cooper and female named Baby 1 Little Corella male named Frankie and have 5 Cockatiels three named Male named Pepper, Fiesco for the female and female named Wylie.
They have to go through first molt to be able to tell which is about 8 months. If your cockatiel molted already then she likely a female. The barring on the tail and dull orange patch on face is how I tell. Plus males talk more, females generally are not that vocal and will hiss where males typically don't.