Architectural Scale Rulers

Reading an Architectural scale Ruler

It is not as difficult as it first appears.

Keep in mind, We are Cabinetmakers and not Carpenters, So the breakdown is of a foot, in 12ths (inches) and not 16ths or 32nds like a regular tape measure.

Thats ok

Because on a drawing, the fragments of an inch are too small to decipher. 

Because 3" fits into 12" (one foot 1' ) four times, 3" = 1'-0"

On plans, It is often written as a ratio of

1 : 4

In imperial the scale is written in a fraction.
1 1/2" = 1' 
or
1.5 / 12

so the Ratio is 1:8
The unit of 12" (1') is shrunk down to the unit of 1 1/2" (1.5")

However as you can see, if the unit of measure is changed from 1' to 1", the ruler can be used to draw in 1/2 scale (1:2) or 1/4 scale (1:4) and so on..

In Metric, The scale is only represented as a ratio, because there are no fractions

Find the scale on a drawing in class