Formula for shipping sizes

My client has a product that is available only in quantities of 1, 2, or 3. A single item ships in a box 8"x5"x5". But 2 or 3 items will ship in a box 14x8x5. In the checkout wizard for UPS shipping one must list the length, width, & height. I see that the lightning bolt lets me connect to a field, so I added three fields to "Items" -- ItemLength, ItemWidth, & ItemHeight. Is there a way to dynamically populate these fields with a size based on the Quantity?

so only the height and width will change.

Create 2 calculations in the eCart object:

height:
abs([Quantity] == 1)?[ItemHeight]=8:[ItemHeight]=14

width:
abs([Quantity] == 1)?[ItemWidth]=5:[ItemWidth]=8

hard set the length at 5.

this doesn't seem logical to me. There's no accounting for the 1 item box and the 2-3 items box. Should it not be something like:
abs([Quantity] == 3)?[ItemHeight]=8:[ItemWidth]=14
abs([Quantity] == 2)?[ItemHeight]=8:[ItemWidth]=14
abs([Quantity] == 1)?[ItemHeight]=8:[ItemWidth]=5

the calculation is using a ternary expression.

a ternary expression is a shortened if statement using the following format:

expresion?true statement:False statement

in other words, this statement:
height:
abs([Quantity] == 1)?[ItemHeight]=8:[ItemHeight]=14

means:
Quantity == 1?

yes: Set the Item Height to 8

No: Set the item height to 14

the height be set to 14 if the quantity is anything other than 1. Set the quantity to 2 or 3, the height will be set to 14