That pump says 1/2" which usually means inside diameter not outside diameter. That's the case with all the kit i have just got anyway.
Here are some popular tubing sizes. I have put ID and then OD with mm in brackets.
1/4" ID (6.35mm) - 3/8" OD (9.525mm)
3/8" ID (9.525mm) - 1/2" OD (12.7mm)
7/16" ID (11.12mm) - 5/8" OD (15.875mm)
1/2" ID (12.7mm) - 3/4" OD (19.050mm)
There's also metric as well,
8mm ID - 10mm OD
8mm ID - 11.2mm OD (Tygon R3603)
This is by no means all that are available. Just the most popular selections.