How to read an architect's scale ruler

Written by carol reeves | 13/05/2017
How to read an architect's scale ruler
An architect's scale is typically triangular. (architects tools image by Chad McDermott from

Architects use a triangle scale to make their drawings. The triangle scale is the one most often used because it gives the architect the ability to use a variety of scales in one instrument. There are typically 12 scales on a single triangle scale, and in Britain and other metric countries, these scales refer to ratios rather than units of measure. The scaled rulers are used to draw building plans and for checking the dimensions when a building is under construction. Architects use the scale to measure out and draw the lengths of walls, doors and windows on paper in a way that will represent the building's real-life proportions.

Find the edge of the ruler that has the 1:10 designation on it. On the British scale the first number in this paring represents mm and the second represents ythe real life measurement amplifying factor so with a 1:10 scale each milimetre on the plan means 1 cm in the finished building and 10 cm on the plan shows 1 metre in real life. Because there are several different scales available to architects, it is usual for the scale used in drawing the plans to be written in the specification section on the plan.

Place the 1:10 scale on the piece of paper that has the floor plan you want to measure. Start with one wall on the outside perimeter, making sure to measure the outside line of the wall.

Align the "0" mark on the 1:10 scale with one end of the wall you are measuring. The numbers that correspond to the 1:10 scale are in increments of 1 mm.

Find the end of the wall you are measuring. Read the number on the 1:10 scale that is closest to the end of the wall. If the end of the wall does not exactly line up with a number on the 1:10 scale you will need to move the scale to the nearest whole number less than the wall length. The number that you read at the end of the scale is your total measurement in mm for the wall you are measuring. Write this number down.

Multiply the number of milimetres you measured by the scaling ratio, so if you measured 20 cm, times that by 10 to show 2 metre wall.

Things you need

  • Architect's scale
  • Floor plan

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