World Airport Codes

https://www.world-airport-codes.com/

Alphabetical Index of Airport IATA Codes

http://www.azworldairports.com/indexes/p-apiak.cfm

Singapore Customs

http://www.customs.gov.sg/

Calculating the Volumetric Weight of a Package

http://www.online-calculators.co.uk/volumetric/weight.php