G'day Carl,

Unfortunately, there is no size chart for the Deuter Airlite 20 SL Daypack. To try and give you a bit of an idea of the fit, this model is an SL which is considered a women's fit, so the shoulder straps will be centralised a little more than usual. The other consideration is that the height of the bag is 50cm which should fit your height of 5'1' okay but naturally, we can't be certain until you actually get it on your back and see how it physically feels.

G'day Shala, 

In general, the Deuter Airlite back system is probably the best for travelling to tropical areas, as it has the mesh back system, plus the straps are very lightweight so they'll be more breathable.

As far as size, if you're going to need to carry things like snacks, an extra layer, and more than one drink bottle - the 26L size is going to be your best bet. Most day packs are around 30-35L, so I don't think this is going to be too big for you.