If you work out the volume in cm then just divide by 1000 will give you litres.......
Lenght X Width X Depth in centimetres divided by 1000
so........if you had a Container measuring 8cm X 8cm X 6cm = 384 cm3 which is .384Litres
Split your box in to separate containers work out the volume of each and add together... simples
Having worked in IT for a good while now... Buy a Dell from Dell
Don't buy a Dell from anywhere else !!!!
An initial purchase from a shop (such as "where in the world" ) may be ok initially , but if you need any support it would be like you asking me to fit a Turbo Charger to your Zed.......... I don't think so.
JMO