Access Number Data Type Field Size

• Byte — Use for integers that range from 0 to 255. Storage requirement is 1 byte.
• Integer — Use for integers that range from -32,768 to 32,767. Storage requirement is 2 bytes.
• Long Integer — Use for integers that range from -2,147,483,648 to 2,147,483,647. Storage requirement is 4 bytes. 
• Single Use for numeric floating point values that range from -3.4 x 10E38 to 3.4 x 10E38 and up to seven significant digits. Storage requirement is 4 bytes.
• Double Use for numeric floating point values that range from -1.797 x 10E308 to 1.797 x 10E308 and up to fifteen significant digits. Storage requirement is 8 bytes.
• Replication ID Use for storing a globally unique identifier required for replication. Storage requirement is 16 bytes. Note that replication is not supported using the .accdb file format.
• Decimal Use for numeric values that range from -9.999... x 10E27 to 9.999... x 10E27. Storage requirement is 12 bytes.
  
  For best performance, always specify the smallest sufficient Field Size.
  
  (Quoted from Microsoft.com)