1. Construction Numeracy
Calculating Ratios and Proportions
Stonemasonry Department 2012

2. Perimeter
‘a ratio represents, simply,
for every amount of one
thing, how much there is
of another thing’
Wikipedia 2012

3. Ratios
Ratios are used by all trades in the construction industry. One
of the most common uses for ratios is when specifying a mortar
mix. For example the image above shows that in order to mix
the specified mortar 5 buckets of sand and 2 buckets of lime are
used. This is known as a 5:2 mix.

4. Ratios
Can you identify the ratio of sand to lime in the mortar mixes
shown below?
= 4:1
= 3:1
= 3:2
= 4:2

5. Ratios
In the last example on the previous slide we established a ratio
of 4:2. When using ratios we normally try to reduce them to
their simplest form. This means that rather than saying 4:2 we
divide each side by 2 and get a ratio of 2:1.
:
:

6. Ratios
Which of the ratios shown below is the odd one out?
That’s right the 5:2 is the odd one out as all the others are
variables of 3:1.

7. Ratios
It is not only mortar mixes that are shown as ratios. In the
construction industry workers are often placed into small
squads so that they are able to work efficiently. An example of
this is the bricklayers 2 and 1 squad where one labourer is
assigned to work with 2 bricklayers.
:

8. Ratios
In previous examples we simplified the ratios to make them
more easy to understand. We can however also multiply ratios
to calculate how many of one value we need in proportion to
another value. Using a ratio of 2:1 can you calculate how many
labourers are required to service 40 bricklayers?
: x20

9. Ratios
We can also have ratios which show the value of three or more
different things. We have now added some colouring dye to our
mortar mix from earlier. Can you guess how the ratio might be
displayed?
5:2:1
The mix is now referred to as a 5:2:1 mix as there are five parts
sand to two parts lime to one part colouring dye.

10. Developed by The Stonemasonry Department
City of Glasgow College
2012