I have a 12 day old brown leghorn just wanted to no if it was a girl

[rural mouse]

Anyone no if it’s a girl

You won't have to wait until this one is 6 weeks. When the breast feathers start coming in, you'll know. Roos of the breed have black breast feathers, hens don't.

Hen

Roo (he was only half, but he popped the color)

 

[SilverBirds]

Welcome to BYC!
She's much to young to sex. Post some pictures when she's 4-8 weeks old.

 

[Tookie]

Hello and welcome to BYC! Glad you joined!

As already stated, your chick is too young to sex. But you shouldn't have to wait too too long, cause if that's a boy it'll pop that comb up early.

 

[Yorkshire Coop]

Welcome to BYC @Williamsmitty2443

 

[chrissynemetz]

Hello, and welcome to BYC! We're glad you joined us!

 

[N F C]

Cute chick, hope you get what you want (whether it's male or female).

 

[LaFleche]

Welcome to BYC!

With her long and dark eyeliner, your chick looks like a pullet to me.
As you can see in this picture, a male would not show this much eyelid line :

https://www.startpage.com/av/proxy-image?piurl=https://www.backyardchickens.com/content/type/61/id/5603675/&sp=1691611796T6e0d0ba4f937f285987661e75e2836859a839e76829d200cbb8e626c513497e0

Edit to add a picture of my own Kraienköppe chicks for comparison: left one is a pullet, the one on the right is a cockerel:

 

[Nomadicus]

Hello and Welcome to BYC! Glad that you joined our community.

 

[triciayoung]

Welcome. Like everyone else said - too young to sex.