Scale

Assessment

In your Assessment at the end of this Unit, you will be asked to:

  • Describe the purpose of scale and proportion in engineering drawing.

This will help you satisfy assessment criterion 1.3 for this Unit. You’ll find lots of useful information on the following pages to help you complete this part of your assessment.

One of the most important aspects of engineering drawing is making sense of the scale that is used. The scale of a drawing shows a full size object with accurate sizes reduced or enlarged by a certain amount. It is the ratio of one measurement against another. It’s important to make sure that the scale is not too big or too small, so that the detail is clear and that the drawing fits on the page!

Using scales appropriately is really important, as it allows us to show small objects as larger than they are, so that engineers can understand them, and it also allows very big objects to be drawn on normal size pieces of paper! Essentially, if scale is used correctly, a component of any size can be accurately drawn and interpreted.

Think first

Can you think of any ratios that you have encountered before? Make some notes in the box below before you move on.

The scale is shown on a drawing in the format of the reduced or increased size, then a colon (:) then the size of the full size object. For example, if a drawing had a scale of 1:10, 1mm on the drawing will represent 10mm on the real object. Click on the tabs below to reveal some of the most commonly used drawing scales.

  • Details

    • 1:1
    • 1:5
    • 1:10
    • 1:20

  • Component Drawings, Assembly

    • 1:20
    • 1:10
    • 1:5

  • Floor Plans, General Arrangement (GA)

    • 1:40
    • 1:50

  • Location Plot Plans

    • 1:80
    • 1:100
    • 1:200

  • Location Plans

    • 1:500

  • Block Plan, City Maps and larger

    • 1:1000
    • 1:1250
    • 1:2500

  • Ordnance Survey Maps

    • 1:100000
    • 1:50000
    • 1:25000
    • 1:10000

Handy hint!

To work out how big part of a drawing will be on the real object, simply multiply the first number in the ratio by the second. For example, if the drawing scale is 1:50mm and the drawn object measure 10mm, just multiple 10 by 50! This reveals that the size of the object in real life will be 500mm.

Now lets move on to the next page to learn about proportion in engineering drawings!