Weight is more often than not, as far as I'm aware. This also ties into questions about refuelling: there's certainly cases where freighters have a choice of ca

Weight is more often than not, as far as I'm aware. This also ties into questions about refuelling: there's certainly cases where freighters have a choice of carrying more freight and requiring a refuelling stop _or_ flying non-stop. How much the time-sensitive cargo is paying decides questions like that.