Just to build on the earlier comment regarding how the size affects the weight charged.
The process is called 'Volumetric Weight Calculation'.
All airfreight is based on an assumption that a certain size of package will weigh at least 1 kg.
Any package is measured and then the mimumum 'weight' calculated using a 'Divisor'.
Currently DHL use a divisor of 5000.

So, if a package measures 100cm x 50cm x 10cm then the calculation is
( 100 x 50 x 10 ) / 5000 = 10kg

That is the minimum you will be charged.

Sorry for the verbage but I worked for DHL for 20 years in this very area.

I guess it is worth knowing if you are considering sending fairly light items (keep the packaging small).

Cheers
Ricky