All technical drawings use what are called scale drawings. A scale drawing is a drawing of something that is 'scaled' so that the drawing fits on a piece of paper that can then be given to people such as builders, trades people etc. and in Australia we use the measurements in millimetres (mm).
For instance, if you measure up your house then went to draw it on a piece of paper, if you measured a 2 metre long wall, then you would need to have a big piece of paper just to draw it on there. This is where scaled drawings come in.
In this instance, we can use a piece of paper then draw a line on it that represents the 2 metre long wall, but only a fraction of the size of the life size wall. This is what is called scaled. We take one length, then convert it into a smaller size (in this case), then draw a smaller line to represent it.

Techical drafting people usually use specially designed rulers called scale rules or line gauges. They look like a normal ruler you would have seen but have different increments, and spacing between increments.
Fig.1 below is a Typical Ruler, and I am going to show you how to use a normal ruler to work out the scale. As I mentioned before, a proper scale ruler will already be adjusted so you don't need to do this.

Fig.1 Typical Ruler (mm)
The Typical ruler each black line equal 1mm in real life length. So the number 1 on the ruler would be 10mm (or 1cm)
1 metre (m) = 100 centimetres (cm) = 1000 millimetres (mm)

Below are the differences between the normal ruler and a certain scale. You will notice the different numbers in red

You will notice to things on each ruler. 1:50 and 1:200 in the bottom left corner of each image of the ruler. What these numbers means are for every 1 unit = 50 units (or in this case 1mm = 50mm)
Going back to my example of the wall earlier, lets imagine this time we measured a 1/2 metre long wall (500mm), so we would need a 1/2 metre long ruler. (Note: 1/2 metre = 500mm or 50cm)
We would also need a piece of paper at least 1/2 metre (500mm) wide in real life meaurements.
This is where the scale ruler comes in.
If we use the 1:50 scale ruler, we could measure from 0 to 10 on the ruler to get 500. The 500 represents 500mm, so exactly 1/2 metre.
So we could easily draw a line that length on paper 100mm wide (10cm or 10 on the ruler)

Another example, say we measure a wall 300mm wide in real life, and want to draw it on paper. We either need a piece of paper 300mm wide, or scale the measurement down so it fits on a smaller piece of paper.
If we look at our 1:50 scale ruler, 300 lines up with number 6 on the ruler. So if we draw from 0 to 6 on a piece of paper we could fit the line on a piece of paper 60mm wide (6cm)

Hopefull this is making sense at this stage.

Next we will look at the 1:200 scale ruler. You might be wondering which scale to use. There are some general rules for certain types of drawings that I will add later on the page.
To understand it though, the bigger the distance, the bigger the scale you will need to go up to get the measurement on the paper. If you were using A3 sized paper, and wanted to draw 10 metres or 10 kilometres, you would need to choose the appropriate scale to fir the paper in most cases.

Lets say we now want to draw a 2 metre (2,000 mm) long wall again on a piece of paper. We either need a 2 metre (2,000 mm) wide piece of paper, or we can use a ruler and a 1:200 scale to fit on a smaller piece of paper.
Using the ruler, to draw a line that represents the 2 metre wall, we could draw a line from 0 to 10 on the ruler, as you will note the 2000 number in red above 10, and that represents 2000 mm (2 metres)

You can use this method for any scale required using a typical ruler. All you need to do to create a scale ruler using a scale rule is multiply the scale required by the ruler increment.
In case of the 1:200 scale, 5 x 200 = 1000. (See below)
You can see that if we take the desired scale of 1:200, we take the 200, multiply by 5 and that would equal 1000mm

The same is with any scale.
The 1:50 scale if we multiply 8 by 50 we get 400mm


Drawing Type: Scales for House Plan Drawings
Site Plan 1:200 / 1:250 / 1:500 / 1:1000 (Typical)
Floor Plans / Roof Plans / Electrical Plans 1:100 (Sometimes but rarely 1:50)
Elevations 1:100 / 1:50
Sections 1:50 / 1:100
Details 1:2 / 1:5 / 1:10 / 1:20
Joinery 1:50 / 1:20

In addition to the information I provide for designing and drafting your own house, I have another side project that tells you how long a house or land has been For Sale or Rent in Australia.
It is also Free to Use and also has a search to give you a price range indication of house and land for sale that doesn't have a listed price.
It is called Get House Date Mobile Friendly too.