Thursday, December 4, 2014

How much does a millstone weigh?

Not far from the college where I teach is an old millstone laying decoratively on the ground.

I've been doing some research on millstones lately so I was wondering how much a typical millstone like this would weigh.  Measuring it gives the following dimensions:

   Diameter = 53 in
   Thickness = 8 in
   Hole = 13 in square

This millstone happens to be made of Shawangunk conglomerate which is composed almost entirely of quartz.  All geologists know the density of quartz which is 2.7 g/cm3.  I want to keep everything in more familiar units so that corresponds to about 0.1 lb/in3.

The volume (V) of the millstone would be:

   V = π (d/2)2 t

where d is the diameter of the millstone and t is the thickness.

   V = 3.14 (53 in / 2)2 (8 in)
   V =  17,641 in3

We have to subtract out the volume of the square hole in the middle (13 in * 13 in * 8 in = 1,352 in3)

   V = 17,641 in3 - 1,352 in3
   V = 16,289 in3

Now we can multiply this by the density of quartz to get the weight of the millstone.

   Weight = 16,289 in3 * 0.1 lb/in3 = 1,629 lb

Over 3/4 ton!  Imagine moving this many miles, over rough terrain, with man power, a wagon, and maybe a mule or two.


  1. Which is why they cost about $2000, if you can find one

  2. Do you have any data on the dates these millstones were mined? Before steamboats and railroads it would take quite a bit of effort tyo move these big rocks!

    We have similar outcroppings to make millstones in East Tennessee and the earliest grist mills appeared in the late 1700s. While the French Burrstones may have been easily delivered in the 1880s, the earlier mills used local product which was claimed by the State Geologist in 1855 to be as good as the French burrstones.

  3. Mid-1700s to mid-1900s. Started before railroads and were originally moved by sledge and horse-drawn carts.

  4. May I have your permission to use the photograph of the millstone in an article I am writing? I will of course credit it to this blog.