Can I turn a regular greeting card into a postcard if I cut off the inside flap?

[VilmerFud]

If so, do I have to do anything else to turn it into a postcard?

 

[sue]

Just check the usps website or at your post office for size limits for postcards. The PO doesn't like square cards or envelopes, for example, and charges extra postage for them.
Then just draw or imagine a line down the center of the card so your message can go on one side and the address, return address and stamp on the other.

 

[Lauren1]

As long as it has a stamp and the name and address written clearly, you should be able to send it

 

[Piggy]

That should be fine, providing the card is firm enough (too flimsy and it might not survive posting and delivery). Check the size in case there are different rates for different sizes. Have the left hand side for the message and the right hand side for the address and postal code. Make sure there is enough room for the stamp. If the postal service says there is a problem, you could always put it in an envelope and send it that way!