I have a keypair. How do I determine the key length?

openssl rsa -in private.key -text -noout

The top line of the output will display the key size.

For example:

Private-Key: (2048 bit)

To view the key size from a certificate:

$ openssl x509 -in public.pem -text -noout | grep "RSA Public Key"
RSA Public Key: (2048 bit)

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