edit: changed shipping to delivery, to avoid confusion.
I would say not exactly based on weight, but similar to that: total dimensions&weight converted to dollars + miles converted to dollars + hours converted to dollars.
> What about 100, 1-lb boxes vs 1, 100 lb box?
Nit: Very few services will allow you to send a 100 lb box. Anything over like 40 lbs is a hazard per OSHA and requires special treatment.
Anyway, besides that, delivering lots of small boxes isn't harder than delivering one giant box if the fulfillment side is doing its job.
> But then you also need to have accurate weights and dimensions.
Everything you buy from Target already has these.
Full Disclosure: I work for Target/Shipt and my opinions are my own.