OT: pints, pounds (Was: APL\360

Philip Belben philip at axeside.co.uk
Tue Feb 9 12:07:04 CST 2021

> On 01/02/2021 20:07, Fred Cisin via cctalk wrote:
>> A US pint of water weighs 1.043 pounds.
>> One "fluid ounce" (volume) of water weighs 1.043 ounces (weight)!

The nit-picker in me would say "you mean mass", except that there's an 
even bigger nit to pick - the density of water is not constant but 
varies with temperature!

> <grin> That's also a US measure.  An imperial fluid ounce is 28.4ml and 
> a floz of water weighs 28.4g, same as an avoirdupois ounce.  In fact 
> it's defined (or was) as the volume of water that weighs one ounce.

The volume that weighs one ounce at what temperature?  I think it may be 
4°C - the temperature of maximum density.

I often wondered why the US fluid ounce wasn't the same size as ours.  I 
always assumed that it was measured at a different temperature, until 
someone said it was from a different definition of the ounce - not 
avoirdupois, but one of the other systems.

The other day I looked up to see whether the density (assuming one ounce 
avdp) corresponded to a temperature that made sense, and it turns out it 
corresponds to water at 100°C.  Not that my data tables gave a density 
for water at 100 degrees - but you can extend the line and there it is. 
  I have no idea whether that is how the unit is derived.  The 
definition is in terms of cubic inches, which doesn't help settle the 


More information about the cctalk mailing list