Understanding Scales and Scale Drawings - A Guide (2024)

Scale drawings allow us to accurately represent sites, spaces, buildings and details to a smaller or more practical size than the original.

When a drawing is described as ‘to scale’, it means that each element in that drawing is in the same proportion, related to the real or proposed thing – it is smaller or indeed larger by a particular percentage.

If something is ‘drawn to scale’ we expect that it has been drawn, or printed, to a common scale that is used as standard in the construction industry. As we gain a better understanding of scale, we can view a drawing in a particular scale and instantly recognise and understand the spaces, zones and gain a quick understanding of the existing or proposed spatial relationships.

In the real world, one meter is equal to one meter. A drawing at a scale of 1:10 means that the object is 10 times smaller than in real life scale 1:1. You could also say, 1 unit in the drawing is equal to 10 units in real life.

As the numbers in the scale get bigger, i.e. 1:50 – 1:200, the elements in the drawing actually get smaller. This is because in a drawing at 1:50 there is 1 unit for every 50unit in real life. A drawing of 1:200 is representing 200 units for every one unit – and therefore is showing the elements smaller than the 1:50 drawing.

It is worth noting that scale drawings represent the same units. So, if a drawing is at 1:50 in cm, 1cm in the drawing will be equal to 50cm in real life. Similarly, if a drawing is in mm, at 1:200 – one mm unit in the drawing will represent 200mm in real life.

The image above shows an example of a drawing set with different scales to demonstrate different aspects of the design. (cad drawing courtesy of bibliocad.com). You may want to represent a site plan at a scale of 1:500, but perhaps show floor plans at 1:100 for example.

Working with scales for architectural representation

In architecture, we use a collection of standard scales to represent our designs. For example, it is common practice to produce floor plans at a scale of 1:100 (dependent on size of project and paper). Once you gain an understanding of scales, it is easy to understand which scale is most suited to which type of drawing.

Scale bar blocks courtesy of cad-blocks.co.uk.

These scale bars show what one unit represents at different scales.

The general requirement of a scaled drawing is to convey the relevant information clearly with the required level of detail. If you are working in practice there will often be office standards. For example, they may only use layout sheets of either A3 or A1 – depending on the scale of the project and information that is being represented. As a student, you need to make these decisions based on industry standard. It is always best to use a ’round’ scale, i.e., one of the scales mentioned below, and not make up your own.

What scale should I use?

The following looks at the recommended scales for architectural use in the metric system. The chosen scale and paper size will often depend on the size of site/design of each individual project.

Location Plan and Key Plans

1:1250 (often requested by planners)

1:1000

1:500

Site Plans, Sketch schemes etc

1:200

1:100

Plan drawings – floor plans, elevations, sections

1:100

1:50

Room plans, interior elevations

1:20

Component / detail drawings

1:10

1:5

Working out the scale

A scale is shown as a ratio, for example 1:100.A drawing at a scale of 1:100 means that the object is 100 times smaller than in real life scale 1:1. You could also say, 1 unit in the drawing is equal to 100 units in real life.

So, if we were drawing a table that measured 100cm wide by 200cm long at a scale of 1:50, you would draw the table 2cm wide by 4cm long on your piece of paper. This is worked out by dividing the real life size (100cm) by 50 (1:50 scale). This gives you a result of 2cm. For the length of the table we divide 200cm by 50 to get a result of 4cm.

Of course, it is not necessary to calculate the required measurements when you draw. You can either use a scale ruler to hand draw your plans, or software such as Revit, AutoCAD, ArchiCAD that will allow you to present your drawings at any scale and easily switch between scales as required.

How to use a scale ruler

A scale ruler is a tool that architects, engineers and designers use to draw their designs at an appropriate scale that it fits on a piece of paper and is in proportion to accurately convey the scheme. The scale ruler comes in different shapes, flat or triangular but they all provide sets of graduated numbered spaces, that establishes aproportion of one unit to thespecified unit,i.e. different scales. As an example, the ruler I have in front of me now has the following scales; 1:1, 1:100, 1:20, 1:200, 1:5, 1:500, 1:1250, 1:2500.

Scale rules have varying number ofscales on them, depending ontheir intended use. Using a scale rule is pretty easy when you know how.

When you are drawing a plan, you select the scale you intend to use by turn the ruler to the appropriate side. You can then draw the line to the desired measurement using the scale ruler. For example, if you have select to draw a 5m wall at 1:100, you would select your 1:100 side of the ruler, and draw 5 units along the ruler, as each unit represents 1m.

When you are reading plans, you establish the scale of the drawing or plans, and select that scale on your ruler, you are then able to measure the lines using the correct scale.

How to scale a drawing up or down

Let’s look at converting a scale drawing to a different scale. You can considering changing the scale of a drawing by a decimal factor or by a percentage. For example, lets imagine we have a drawing at 1:50, but we want amend the scale, to show that drawing at 1:200. A drawing at 1:200 is 4 times larger than a drawing at 1:50, therefore we would need to increase the size of the drawing 4 x. The table below demonstrates the different scale factors required to convert a scale up or down.

Table: Converting scales up or down

Being able to scale drawings up and down using percentages has become very useful too. Working in Adobe (Photoshop, InDesign etc), you will find you can adjust the size of an object using a percentage, which is great if you are wanting to accurately scale a drawing up or down while working in photoshop while maintaining a precise scale.

Lets imagine you are working on a drawing that you have imported into an A4 sized photoshop document. The drawing you have imported does not quite fit at its current scale of 1:50, so you will need to reduce the scale in order to squeeze the image onto the page, while maintaining an accurate scale. By using the table below, we can see that to convert from a scale of 1:50, down to 1:100 we would need to reduce the drawing by 50%. To do this we would make sure the dimension ratios of the image are locked, and proceed to type 50% into the size box.

Obviously this is a simple example but you get the idea. The table below provides the basic conversion percentages to scale a drawing up or down using the standard metric scales.

Table: Converting scales up or down

Paper size scales and magnification

We can now look at amending paper size scales and magnification. There are times when you may have a drawing on an A4 piece of paper, that you need to scale up to an A3 piece of paper for example. Let’s imagine you were needing to trace this drawing so would use a photocopier to scale the drawing up to the necessary size.

How to convert paper sizes?

To convert the paper size you can use the percentages in the table below. Note that these percentages do not correspond to the scale factors. So, if you scale or magnify a paper size accurately, it does not mean that you will retain an accurate (or standard) scale of the drawing. So, if you want to increase the scale of a drawing using a photocopier, but want to increase it to a standard scale (1:10 for example) then you must use the percentage factors for converting scale. If it is just the paper size you wish to change, then you can use the paper size converter. I hope that makes sense.

Table: Converting paper sizes and magnification factors

Working with paper sizes

When working with ISO paper layouts we know that the standard size of paper was developed on the basis of an area of 1m2, divided according to the ratio of the sides.

This basic format of 1m2then forms the basis for all other smaller sizes. All A sized paper is either halving or doubling the basic format.

X x Y = 1

Below is a list of all the A paper sizes.

Working with scales digitally

One of the great things about using digital drafting software is that you can produce drawings as multiple scales from one single drawing. Programs such as Revit, AutoCAD, ArchiCAD and many more, allow you to draw up your designs at 1:1 scale, that is real life size, and produce drawings or plots of these designs at an appropriate scale for the paper size you have selected.

When working in CAD you can let the software do some of the hard work for you by making use of the paper space option to create layouts. On your layout sheet you are then able to create viewports which feature your drawing at the required scale. I have recorded a couple of tutorials that will help with setting up drawings for printing at appropriate scales.

You can download my dynamic scale bar cad blocks here:

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