If you created your key pair using AWS, you can use the OpenSSL tools to generate a fingerprint as follows:
$ openssl pkcs8 -in path_to_private_key -inform PEM -outform DER -topk8 -nocrypt | openssl sha1 -c
If you created a key pair using a third-party tool and uploaded the public key to AWS, you can use the OpenSSL tools to generate the fingerprint as follows:
$ openssl rsa -in path_to_private_key -pubout -outform DER | openssl md5 -c