In the simplest case of a purchase there are two things which
are knownthe Quantity (how many/much) and the Cost per unit (or
item)Then multiplying these two together givesthe Total cost and
this can be done in the top part of this calculator.It can also
be used to work out what the 'Cost per unit' was if the
'Quantity' and 'Total cost' are known. Or the 'Quantity' if the
other two are known. In other words, given any two values out of
the three, the third can be worked out. And so, values can be
entered in any two (out of the three) boxes at the top (and in
any order). To do any of that it is not necessary to know what
units are being used to measure whatever it is. However, if
required to make comparisons between different prices which are
given for different units (like 11.50 per cubic metre and 8.99
per cubic yard) then it is necessary to know just what units are
being used for the purchase. This information is given under
'Comparative Costs per Unit'. Just make sure that, at the top,
the entry under 'Cos