Work out secure erase time instantly with clear inputs, formula shown and shareable results.
Overwrite time is capacity times passes divided by sustained write speed, which makes multi-pass erasure of large drives take many hours each. Cryptographic erase destroys the drive's internal encryption key instead and completes in seconds, which is why NIST SP 800-88 treats it as the preferred method for self-encrypting drives and for SSDs, where overwriting cannot reach over-provisioned blocks anyway.
Erase time
per drive = capacity x passes / write speed (cryptographic erase is near instant); total = per drive x drives
For magnetic drives, yes. NIST SP 800-88 states a single overwrite pass renders data unrecoverable on modern drives; the old multi-pass folklore predates current areal densities.
Wear levelling and over-provisioning mean the controller may not expose every physical block. Use the drive's sanitise or cryptographic erase command instead.