I Need a little help with Formula to calculate weight etc.

[carl97]

Hi everyone I am back again.
I have come a bit stuck again.

I have recently added iferror statement to my table but it is not working as i expected.
I am trying to Create a Value for Item names and add weight to the item then calculate aditional weight like envelope etc.
then to inform me what envelope size to use and then calculate recently added (So i can update) postage fees.

The complications i had where with the weight and size. If the weight was over 750g then the tarriff would be "Parcel".
I have setup the limits of how many items each envelope can handle to stay within the Large Letter size (UK Postage Tarriff) as the next step is "Parcel"

Two criteria occur.
If it is over 750g then it is a Parcel
If it is thicker than 25mm then it becomes a Parcel Ref Envelope Size F3B, P1A-P1D (I made these up myself)
Everything else that is 750g or below and under 25mm then it is: Ref Envelope Size A000, C0, E2, F3 (Official Sizes)

When it is larger that F3 then i stack upto 5 x F3 and assemble as a single package. F3B is a double thick single package F3 making Parcel Size.

I have added my Workbook if anyone would like to guide me in the right direction.
I have tried to make it as clear as possible but i know i could probably do better.