Given an address (i.e. 1BnPVV5Tt25cxbDg6DqoxJunjSL8reCGz6), how can I calculate its scriptPubKey in order to build a transaction?
I assume you want to integrate it into a P2PKH tx. You would have to base58decode the address, and then remove the checksum and the network byte. Then you can integrate it into a P2PKH tx in the std. way:
76 A9 14 <20 Bytes> 88 AC
I have two references with some code examples in C and python, that helped me at the time, when I had the same question :-)
and some online "play tools" to verify: