Always, MTU > MSS
Without any TCP or IP Options in the packet:
MSS + 40 Bytes = MTU
The 40B is used to represent 20B of IP header and 20B of TCP header. The addition in number of bytes can be more than 40B depending on options in the header.
Standard Ethernet Frame: 1500B. Ethernet Header and CRC: 18B. MTU refers to Ethernet Payload without the header and CRC.
Ethernet Fram Size = Header + Standard Ethernet Fram (1500B) + CRC