Understanding Scales and Scale Drawings

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Understanding the concept of architectural scales and scale drawings


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 50 unit 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.

Stadium plan - scale example


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 bars

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)

Site Plans, Sketch schemes etc


Plan drawings – floor plans, elevations, sections


Room plans, interior elevations


Component / detail drawings


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 a proportion of one unit to the specified 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 of scales on them, depending on their 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.


Scales conversions decimal

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. 

Scales conversions percentage

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. 


Converting paper sizes

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 1m2 then 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.

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.

I have also recorded a tutorial that explains how to scale a drawing in cad. This is useful if you have imported a drawing at a different scale.

You can download my dynamic scale bar cad blocks here:

You can download a handy pdf of this post by clicking the download button below!

Hope you find this useful, if you have any questions, or there is something else you would like to know about, please drop me an email (hello@firstinarchitecture.co.uk) or comment below.

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  1. I have a question, about scaling. I have a 2D site drawing drawing 1:1. The site drawing is referenced on my cover sheet. The cover sheet is set to print at 1/4″ = 1′ but I want the scale of the site plan to be 1″ = 30′. I can’t figure out what the one scale factor is that I can use to scale the 1:1 drawing by to get it to come in to the cover sheet at the right scale.

  2. I have a question,I’m trying to draw a floor plan to scale of 1:50,but the measurement in the floor plan does not express if it is in meter, millimeter etc.. it only give the numbers like total length of the plan 1800, door length 90 etc.. how to draw this plan?

    • If the plan tells you the door width, you can work out what units the plan it in. You know the standard door width generally, is around 900mm – so it sounds like your plan could be in centimetres if it is saying the door width is 90…

  3. Hi there,
    i have a CAD drawing that is drawn in Meters (CAD Unit is meter)
    my page on paper space is on “ISO A1″ 841X594,. i was hoping to plot to 1:50 for equivalent of 1′ = 1/4” but the drawing is as small as a dot.
    i watched a youtube video that explained to do a custom plot scale since my drawing is drawn in meters and the CAD unit is in meter. custom plot 1paper unit to 0.05 drawing unit. when i did that visually the drawing seems okay.

    i have some questions:

    – first of all is this a correct scale?
    – if i am writing the scale under my drawing, what do i put there? 1 : 0.05 ?

    • The easiest thing to do would be to scale the cad drawing up to millimetres, this way the video will make more sense as you work through it. When you then enter the scale in the custom plot area it will be 1:50 and you will write 1:50 under your drawing. To scale the drawing, change the units of the drawing to milimeters first, this is in Tools. Check to see if the drawing lines are still in metres, if they are – Then go into your paper space, select all, type SCALE, ref point 0,0,0 and scale factor 1000. Hopefully this will work. Good luck .

  4. Hi I have various pdf vehicle drawings at various scales and they all need to be at the scale of 1:50. How do I convert in scale percentage from 1:15 to 1:50 scale. 1:35 to 1:50 and 1:10 to 1:50 I’m bringing in the pdf drawings into illustrator and then tracing them so they can all be viewed in at the same proportional scale

    • Hi pls can send a video on building drawing like using scales and all that with the plan where we have bedroom,kitchen etc with the windows indicated and doors

  5. thank but i can’t download this pdf for scales

  6. Hello,

    I’ve got a question regarding the scale on a view port. The scale shows 150 to 1. When l change it to 1:50 which is the scale that I normally use, the drawing becomes very tiny that I cant see anything. Any advise?


    • Hi Ed, is the drawing in the model space drawn at a scale of 1:1?

  7. Hi,
    I have a scale of 1:200 m using the scale ruler. My professor told me to show the computations I did to arrive at my chosen scale factor. Since it is my first time making a lay-out, I am not familiar about it. How can I show my computations?

  8. What would the scale be on A1 if the original was 1:200 on A0?

  9. the floor of a school hall is 40m long and 20 m wide draw scaled diagram in a scale of 1:50

  10. Hi emma. Im studying garden design but not getting the scale ruler. I assumed the ruler was converting it all for you. So 1 metre in reality i was using the 1 marker on 1:50 as thought it was already done. But a 60cm plant in 1:50 ive been told is 120cm on the ruler. Any scale ruler for idiots explanation plse as im now not getting what each whole number represents on each scale side.

    • Hi Jade, I think you were right the first time. The ruler does the conversion for you. So, if you have a drawing and it is at a scale of 1:50. You measure your plant and it is at the 1 mark on your 1:50 ruler, the plant is 1m. Likewise, if you want to draw a 3meter line at a scale of 1:50, you get your 1:50 ruler and draw to the 3 mark. Hope this helps.

  11. Hi Emma. Please confirm which dimensions are placed on a drawing using a scale. For example using a scale of 1:100 and I have a length of 3000mm. Drawing the line on paper it would be 30mm long, is 30mm the dimension placed on paper or would I place 3000mm? Thanks

    • Hello David,
      If I’m understanding you correctly, you are asking what dimensions you should place on a drawing. You always want to place the ‘real life’ dimension on a drawing. So if you are drawing a wall, and the wall is 3m long, you will put a dimension note saying the wall is 3m long – even though you have drawn a 30mm wall. The goal of dimensions is to show the reader/builder the real life sizes of objects/constructions so it can be built. I hope that makes sense.

      • Hi Emma, thank you for your rely. It does make sense:)

  12. Finally a great post on scaling!!! I have a hard time with numbers and never seemed to understand it untill you walked me true it in this post. Many thanks!!! Done pulling my hair out now

    • Thank you!

  13. Thanks for the post, you really did great. I will certainly refer to it if need be.

  14. Hello, hope someone can help me out on this question cause i’m very confused at this point.

    I have a drawing on the model space in cm. I need to plot at a scale of 1:50 on an A0 paper. The units in the paper space are in mm.
    I don’t understand how I should scale it, inorder to get the desired result using the zoom command.

    I tried using a scale factor of 1/5xp but in the preview, part of the drawing is missing, why is that?

    Please, any help would be really appreciated. Thanks in advance!

    • Hi there.
      I think the easiest thing is to make sure the units match in your paper space and model space. That way, everything should work much better when you come to using scales in your view ports etc.
      You can adjust your paperspace by going to the page set up manager while in paperspace and setting everything up in mm. From there, when you scale the viewport, say at 1:50 it should be correct. If you continue to have issues, feel free to drop me an email – emma@firstinarchitecture.co.uk

    • Sorry, one other thing. I would recommend you work in mm in your model space ideally. So convert everything to mm in both model space and paperspace.

  15. Hi there,
    I just wanted to say how useful I found this! Normally I struggle reading masses of information but this was really well explained and I learned a lot. Very much appreciated!

    • Thank you 🙂

  16. Hi and I hope that you can help me here!

    I have a plan drawn to a scale of 1:50 drawn on A3 paper for submission via an online portal to a planning authority in UK.

    Unfortunately my printer/scanner only accommodates paper up to A4 size. I can have my A3 plan sized down to A4 at a local printer so that I can use it on my scanner for transfer to the portal site.

    Will this interfere with the scale drawing when the planning authority look at it? Do I tell them it was originally on A3 and they can size it back up again?

    Or if I just take a photo of the plan, would that work or am I being rather naive here?!

    Many thanks in anticipation.


    • Hi Glenn,
      This is a bit tricky.
      If you have the A3 scaled down then it will no longer be at 1:50 scale. Can the local printer scan the document at A3? Then you can send to planning at its original size of A3 to the correct scale. The Planning department will not scale drawings up or down, they need the drawing to be correct when they receive it.
      A photo of the plan will not be acceptable for the planning department.
      I would recommend speaking with your local printer and seeing if they can scan in at A3 and send you the digital file.
      Best of luck 🙂

  17. Hi. You sometimes see a plan with the scale shown as 1:100 at A3. Isn’t the plan always 1:100 no matter if you change the physical size of the plan (eg change paper size).
    I would have thought that it makes sense to use “at A3” when you use a scale bar which gives you unit measures on that page which would actually change if you changed the paper size. Thanks.


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