An afternoon’s distraction

Background: I was reading an old adventure (specifically The Serpent’s Tooth in Dungeon #19) and I saw a suggested weight of 800 lbs for a barrel of beer. The dimensions of the barrel were given as 2 ft diameter and 4 ft height. I’m not a beer drinker, and I’ve never tried to lift a barrel of beer, but that seemed kinda excessively heavy, and maybe also too-conveniently rounded off, so I was curious about the accuracy. Naturally, I poked around the net for some numbers.

Beer is given by http://www.simetric.co.uk/si_liquids.htm as approximately 1010 kg per cubic meter. Multiplied by 0.0624 equals about 63 lbs per cubic foot. This is just slightly more than pure water.

According to http://www.crafty-owl.com/cooperage.htm, an empty barrel typically weighs 125 to 140 lbs. From Woodweb we can eventually approximate the weight of white oak at 47 lbs per cubic foot (760 kg per cubic meter) at a completely arbitrary 20% moisture content. It’s arbitrary because I can’t find any information on the moisture content of the wood typically used in making barrels. I am sure, however, that white oak is the right choice of wood, and I’ll trust Professor Wengert’s numbers.

Dividing the 125-140 lb barrel weight by 47 lbs per cubic foot, we get a range of 2.6 to 3 cubic feet of wood used in the construction of a barrel… 130 lbs means about 2.75 cubic feet of wood; those are nice round numbers. This is not completely accurate because that weight includes some metal bands used to hold the barrel together, but I don’t have separate numbers for the weight of these bands so this assumes the whole thing is made of wood.

A quick look at Tonnellerie Damy Père & Fils gives the dimensions of a smart-looking 300-liter barrel as approximately 41 inches tall and 31 inches in diameter, with a 25-inch head. It’s not the 4-foot tall, 2-foot across barrel from the description I read, but it does have a weight of 58 kg, which is quite close to the 130 lb average barrel size I arrived at above… which means that a very similar amount of wood is used in its construction, which in turn implies that the internal volume of these barrels should be close. Assuming that the arbitrary 20% moisture content is at least fairly accurate.

So basically, 300 liters of beer is what we’re looking at.

Using http://www.onlineconversion.com/volume.htm, we can convert directly from liters to cubic feet; 300 liters is about 10.6 cubic feet. Plugging in the weight of 63 lbs per cubic foot from above, that volume of beer weighs just about exactly 668 lbs. Plus the 130 lb barrel weight, and we have a total of… um, 798 lbs.

That was anti-climactic. Suddenly 800 lbs looks like a pretty fair estimate.

Side note: another section of the conversion site, http://www.onlineconversion.com/object_volume_barrel.htm, suggests a formula for calculating the volume of a barrel: h * Pi * (2*r1^2 + r2^2) / 3, where r1 is the diameter of the middle of the barrel and r2 is the diameter of the top of the barrel. However, we would need to know the internal measurements of the barrel in order to make use of this, and what we have is the external measurements, so it’s just a neat formula.

Using the numbers from Tonnellerie Damy here’s a quick list of barrel sizes and weights, in American units.

liters gallons diam(in) ht(in) empty (lb) full (lb)
225 59 28 37 99 600
228 60 28 35 99 607
265 70 28 37 99 689
300 79 31 41 128 796
350 92 33 41 154 933
400 106 33 42 185 1076
500 132 32 43 198 1311
600 159 41 44 220 1556
700 185 41 45 243 1802

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