size of EVP_Seal* output

[Jonas Schnelli]

Hi

I try to pre-calculate the size of a EVP_Seal encrypted buffer (just the seal, 
exkl. keys).
How do i precalculate that? I assume with some blocksize stuff (i'm a crypto 
novice).
I'm using AES256 as EVP_CIPHER.

Thanks for any help
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</jonas>