A scale ruler is the three-sided ruler used by architects and readers of blueprints to convert between scaled drawings and the actual dimensions without having to resort to any mathematical calculations. An architect uses the scale ruler to convert dimensions into a smaller drawing of a building plan. The reader of the blue print will then use a scale ruler to translate the drawing into the real sizes for construction.

### What is a scale ruler?

A scale ruler is the three-sided ruler used by architects and readers of blueprints to convert between scaled drawings and the actual dimensions without having to resort to any mathematical calculations. An architect uses the scale ruler to convert dimensions into a smaller drawing of a building plan. The reader of the blueprint will then use a scale ruler to translate the drawing into the real sizes for construction.

### Choosing the correct scale

On each side of a scale ruler at the far left before the zero mark is a number reflecting the scale of the rules on that particular side. Using the appropriate scale is crucial and should be the first step. If reading a blueprint, the appropriate scale will be written on the plans. If drafting a plan, choosing an appropriate scale will depend on the size of the drawing compared to the actual dimensions described.

### Measuring with a scale ruler

Common scales are 1:10, 1:50 and 1:100. The first number represents the distance as measured on the ruler and the larger number is how many times bigger the feature is in the real world. To read a blueprint with a scale ruler once the appropriate scale is determined, line up the zero mark with the beginning of the length to be measured. If the distance falls exactly on a line of the ruler, that is the measure in metres. Make sure the correct marks are being read, as most scale rulers have two scales per side for maximum efficiency.

If the distance being measured does not fall exactly on a line, the exact measure will be the number of metres corresponding to the nearest line passed plus a certain number of cm. Determining the cm will require a second measurement. Before removing the scale ruler, first mark the appropriate metre line on the drawing. The first cm of the scale ruler is subdivided into tenths, corresponding to cm. Line up the zero line with the mark representing the metre line of the first measurement, and use the detailed marking to find the number of cm. The full measurement will be the number of metres plus this number of cm.

Even with this second step, using a scale ruler is much easier and faster than making complex conversions using maths. It also minimises the chance of error in the calculations. With a little practice, using a scale ruler becomes a simple but essential tool for the contractor and architect alike.