Can I pray with a cap or hat on?

Covering the head is optional for men

For men, the awrah that must be covered in prayer is from the navel to the knees. The head is not included, so you can pray bareheaded or with something on your head. Many Muslim men wear a kufi (prayer cap) because the Prophet ﷺ and his Companions usually covered their heads with a turban or cap, and wearing clean, decent clothes for prayer is encouraged:

Scholars differ on how strongly to recommend it. Some see a head covering as a good sunnah of dress and part of looking your best for prayer; others say it simply follows local custom. Nobody says your prayer is invalid without one. For the full list of what to cover, see What do I have to cover when praying at home alone?

Watch the brim in sujood

In prostration, your forehead and nose should touch the ground. A baseball cap with a stiff peak can get in the way. If it does, turn it backwards or take it off. A beanie or kufi is no problem, since praying with a thin layer between your forehead and the floor is accepted by most scholars, though bare skin on the ground is best.

What kind of hat?

• Kufi or prayer cap: the classic choice, and many mosques keep spares by the door.
• Beanie or woolly hat: fine, especially outdoors in winter.
• Baseball cap: fine if the peak doesn't block sujood.
• Hats with offensive slogans or logos: better avoided, like any clothing with images or messages that don't suit worship.

Going to the mosque for the first time? See What should I wear to the mosque?

What about women?

A woman must cover her hair in prayer, and a hat on its own usually isn't enough because hair, ears and neck still show. See Is a hat or beanie enough as a hijab?