In a current Pathfinder game I'm running the PCs have decided to take multiple wagons full of mundane items to outposts/remote villages/etc., both as bribes and for business purposes. They are frequently asking me questions such as "how many candles can I fit in a standard barrel?" and "if we buy cabbages, apples, walnuts, and pumpkins, how many can we fit in our wagon?"
Since this is apparently the theme they've settled on, I'm going to let them run with it until they devise some other method of... whatever they're doing. My players do genuinely want this kind of detail. In all fairness, I do as well; I like low-magic campaigns, and in those, logistics like this become increasingly important. However, I'm getting stretched trying to ad-hoc reasonable responses to these, and am looking for a sensible approach without a lot of math each time, while keeping to a relative level of consistency.
Is there a ratio relating the listed weights to volume that I can use to help answer these questions? If there's a ratio, then I could take the CRB's given weights for items and multiply by the ratio to obtain a rough idea of the amount of space an item occupies.
Yes, I know everything varies, and a ton of feathers clearly isn't the same as a ton of bricks, etc., etc. I don't want real-world accuracy, I want a reasonably fast, gameable method so I can ensure consistency during play without taking up lots of time. We're mostly dealing with produce, or the standard trade goods listed in most rule sources, so big density differences are not likely to be an issue that needs to intrude on gameability.
What I'm hoping for is a rough decimal/fraction/percentage comparing weight to volume, so I can just plug in "X pounds of item" and then divide into the given container volumes.
I also don't want to keep guesstimating since that has been, from experience, neither fast nor sufficiently consistent. It's a waste of my time as GM.