A bar scale is the graphical representation of size conversion. It is located on maps or blueprints to show how much distance a specific measurement corresponds to. For example: one centimetre on the map may equal 100 meters in real life. Drawing a bar scale is simple but it must be accurate. An inaccurate bar scale causes misinterpretation of the entire image.

Determine the scale of the map or blueprint for a distance divisible by 10. Distances used regularly are 100 metres, 1 kilometre or 10 miles. This information is usually available on the map or floorplan. If this information isn't written on the document, contact the printer for the details.

Find the distance manually, if necessary, by measuring the paper distance between two known landmarks. For example, if you use a map of the UK and know that the distance between your city and another is 100 km, measure this distance on the paper with a ruler. If the length is 1 cm, then 1 cm represents 100 km on the document.

Locate a blank section on the document that is big enough to accommodate the chosen measurement. On most maps, the bar scale is drawn in a bottom corner near the compass.

Draw a straight, horizontal line the length of the chosen scale bar using the ruler. If 1 cm represents 100 km, the scale bar should be one centimetre in length. The line should also be subdivided, at least into quarters. In this example, vertical subdivision marks should be placed 2.5 mm apart.

Label the scale bar appropriately. If 1 cm equal 100 km, the scale will look like this: 1 cm = 100 km. Write the label beneath the scale bar.