Scale Bars

Understanding Scale Bars

November 2019

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To understand what a scale bar is and how it aides drawing and map representation, we must firstly understand what scale itself is.

Covered in detail here; scale is the method of representing a subject at a different proportion to its real world size, although most commonly used as a device to reduce proportions, it can also be used to increase them.

Typically used to represent large objects and areas, such as building plans and maps, scale reduces sizes down to a manageable proportion than can both be viewed comfortable as a whole, and be easily transportable via traditional paper sizes and methods.

...a scale bar is a tool that aides us with the reading of this scale when a scaled rule is not available, and/or the drawing or map is not printed to its intended and specified sizing.

What is a scale bar?

A scale bar is a linear graphic that is divided into equal segments and used to measure distances on drawings and/or maps that are produced to a set scale, but not necessarily printed to one.

Particularly within the design, architectural and engineering professions, in many instances drawings are printed to an exact scale and can therefore be measured via a scale rule. The addition of a scale bar however means that the drawing can be measured using a traditional ruler and/or any other well proportioned object such as a credit card or posit.

As for maps, these come in a variety of shapes and sizes that due to the large area being shown, rarely represent a traditional drawing scale, and a scale bar is therefore the only way to accurately measure distance.

Why are scale bars important?

Aside from making map and drawing reading easier, when a scale bar is present, the drawing or map doesn't necessarily need to be printed to a specific scale. This is because the scale bar, not matter how big or small the drawing becomes, maintains its proportion to the subject.

This is particular useful when measuring via a screen or mobile device, and when a plotter is not available to print the required paper size.

Scale bar types

Scale bars are bespoke to the scale of the drawing or map they are assigned to, and can only be transferred between one drawing to another if both drawings are of the same scale.

For example a scale bar showing an imperial 1:8” scale, can only be used to measure a 1:8” drawing and/or map. If the drawing is of a different scale, it requires a different scale bar to match.

For this reason and in terms of the units used as measurement, there are many variations.

Graphically however, there tends to be a few key and standard methods of representation as shown below, however equally there can be a high level of creatively in the way that the scale bar segments and units are shown.

The one KEY and fixed factor is that the scale bar must be straight.


How do you calculate a scale bar?

A scale bar if often calculated at the time of when the drawing or map is complete and before it is plotted (printed) to a set scale. If for example the drawing is being plotted to a metric 1:100 scale, and the scale bar units are in meters, then each one of its segments will represent 1 meter and be 100 times smaller than the 1 meter real-world measurement.

Equally scale bars can be drawn at a 1:1 scale, and using the relative units of measurement to match the drawing, simply be plotted to the required scale to match the drawing.

How to create a scale bar

Scale bars can be drawn in any imperial or metric unit, however this is most commonly influenced by the size of the subject needing to be scaled.

For example, a floor plan of a house would most commonly be measured in millimetres or inches, but a map that represents a much larger area would be measured in meters/feet or miles/kilometres, and the accompanying scale bars would match this.

How do you use a scale bar?

A scale bar is essentially a measuring aid and device, and whilst it can be used independently, it is typically paired with a standard rule.

The rule is used to take measurements from the drawing and/or map, and then measured against the scale bar using the recorded distance.

Free scale bar CAD blocks

Below are four free a scale bars representing a 1:100, 1:500, 1:8” and 1:16” scales

Related guides

Architectural scale & scaled drawing guide

Architectural drawing symbols guide

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