The Total Length field in IPv4 is a 16-bit field that defines the entire packet size (header and payload) in bytes. The minimum is 20 bytes, which would be the minimum size header (with no options) and no data. The maximum size is 65,535 (216-1) bytes.
In IPv6, a similar 16-bit field is used, although the value does not include the IPv6 header length. If the payload is greater than 65,535 bytes long, the field is set to 0 and it's specified as a jumbo payload.