How to Read Architectural Drafting Using a Metric Scale Ruler

Updated March 23, 2017

Reading architectural blueprints involves looking at drawings, legends and symbols. They can be drawn by hand or created using computer software. Architectural drafting, or blueprints, are drawn using the metric scale in most countries around the world, while blueprints in the U.S. are typically drawn using the English system of measure. Whichever system your blueprint uses, you can use a metric scale ruler to determine lengths and dimensions. Reading metric plans is straightforward but you'll need to apply additional conversion factors for blueprints that use inches and feet.

Roll out the architectural blueprints onto a flat working surface. Look for features on the blueprint that you want to measure. This could be one single line, the dimensions for a room or dimensions for the entire structure. Place the metric ruler at one end of a line on the blueprint and measure the full length of it. For instance, a line along one wall may measure 2mm on your metric ruler. Make sure that the start of the line corresponds with the zero on the ruler.

Look at the blueprint legend at the bottom or edge of the blueprint. Among other things, the legend will tell what scale was used to draw it and what the conversion ratio is. The scale will be either the metric scale or the English system scale. The metric system in its architectural applications uses units of measure such as meters and millimetres, and units in the English system are expressed in feet and inches.Note down what scale and conversion ratio is on your legend.

Convert the measurements taken in accordance with the scale and ratio described on the legend to determine the true size of the actual structure. Use the ruler measurements to calculate actual lengths. For example, if the scale is metric and the ratio is 1:10, the 2mm line would represent 20 meters in a real building. That is, 1mm on the plan represents 10 actual meters, so multiply 10 times 2 to get 20. If the legend uses the English system, you'll need to make one further calculation to convert the 20 meters to obtain the length in feet. Note that 1 meter is equal to 3.2808 feet, so multiplying that by 20 meters would equal 65.62 feet.


1 foot = 0.3048 meters. 1 meter = 3.2808 feet.

Things You'll Need

  • Blueprint
  • Metric scale ruler
  • Calculator
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About the Author

Erin Moseley is an advocate for science education. Since 1985, she has written numerous technical, user and training manuals for major corporations, public agencies and universities. She holds a Bachelor of Science in geology.