This may sound complicated, but the main part is maximum parcel girth + length: 2.8m. All this means is that the combined length of the 5 sides illustrated on the diagram must not exceed 2.8 metres. For a cube-shaped box, this roughly equates to 0.5m x 0.5m x 0.5m.
If you have more items to send than will fit in such a box, just let us know and we’ll be happy to arrange for multiple boxes to be collected.