Crown to trunk ratio?

A neighbor is planning to take down an oak tree in the spring, and I'm trying to guesstimate how much space I'd need to store the wood. The trunk is easy enough to calculate; I haven't measured it, but if it were about 20" in diameter and 15 feet tall, that would be about 33 cubic feet of solid wood. I found a state government document suggesting that S&S firewood is about 70% wood and 30% air space, so that trunk should be a little over a third of a cord. But the geometry gets unwieldy when you start looking at the branches. Is there a rule-of-thumb sort of ratio between the amount of wood in the trunk and the amount in the tree's crown?

I'd say (I don't know) that depending on the tree, the crown could be much more than the trunk.
My point in responding though;
If I am cutting up a tree, I cut the limbs from the outside in. I save everything from about an inch up, working my way to the trunk.
The branch wood is my favorite, I like cutting much more than splitting. The small stuff mixes in the stacks, and I usually have enough small branches to throw on the coals in the morning, never fussing with kindling.

If the tree is a yard tree or shade tree it will have a ton of crown compared to trunk, whereas if the tree is more of a forest tree you can expect a lot less crown realtive to trunk. I think a typical 20 inch diameter tree will have about 2/3 of a cord to maybe a cord.

A cord of wood stacked is 128 cubic feet of wood and air, and normally that includes about 85 or 90 cubic feet of solid wood.

Guesstimate the space close as you can.
Then just stack it higher if you under estimated

Youns still have snow on the ground ?

Still? At this time of year, it's just getting started. We got hit by that blizzard just after Christmas, and have had more snow since then, so we've got about 8" on the ground. I'm new to Pittsburgh, but I'm told it's more snow than is typical for this time of year. It hasn't been very cold yet. But, this is neither hear nor there; it will be a few months before the tree comes down.

Wood duck, that's a good point about the difference between yard and forest trees. I guess my ratio idea isn't likely to be useful; oh, well.

My house is on a fairly steep hillside, without a lot of level areas for wood racks. When I got started back in late September, I built racks to hold a cord and a half on the concrete patio outside the walkout basement. Those got filled with a load I purchased with the intention of burning it this winter, but it arrived at 40% MC (or worse), which I didn't realize until it was too late. So then I bought another 3/4 cord from a different seller, and stacked that on the first floor deck that's over the patio.

The initial bad experience and unexpected expense made scrounging my own wood look more appealing, so I set up a smartphone app to notify me of Craigslist ads for free firewood. Few homeowners seem to have any idea what sort of trees they're trying to get rid of. The first "oak" tree I went after turned out to be a red elm. The next oak was a mulberry. Then came some pine that was actually an overgrown juniper bush. I helped clean up an unwanted woodpile at a burnt-out and formerly abandoned house that was being gutted and rehabbed, and came home with some more mulberry and the trunk of a red oak that someone had left standing after cutting off the top. By this point the deck above the patio was getting crowded, but it didn't matter too much because the weather was chilly and we weren't using the deck much anyhow. But free wood offers kept popping up on my iPod, and soon I was ferrying load after load of black locust from a house in a neighboring suburb, 3 miles away. To a spy satellite I'd look like an ant dragging bug carcases across the landscape back to my burrow. Thankfully I live near the bottom of a valley while the source of the locust was close to the top of a ridge, so the trips home with the locust were mostly controlled descents; my poor Volvo isn't built to haul that much weight uphill.

At this point the perimeter of the deck is lined with wood stacked to the top of the railing, much of which I will have to move somewhere else when spring weather makes the deck more attractive as a living area. And now this lovely and conveniently positioned oak tree comes along. I'm sure I can find room for some of it, but I suspect there's more than I can take without alienating my wife and neighbors. I think I'm going to need to have some simple way of telling the tree service what parts of the oak to take away, and what to leave behind. I don't want to create a situation where the homeowners' yard is full of wood that I can't deal with quickly.