Blueprints use a ratio or scale to show that the image is smaller or larger than the actual size. The ratio is typically represented using a ratio such as “1:100” or “1:2.5” depending on the type of blueprint. A scale is also a type of ruler that uses a ratio to measure blueprints without the need for calculations. Scales exist for architects and several types of engineering, including civil and mechanical, and the ratios for each correspond with the ratios used in that particular field.

Locate the scale size of the blueprints or architectural plans that you are measuring. This information is typically located in the title block at the bottom-right corner. The scale is the ratio of how small or large the drawing is compared with real size.

Locate the matching ratio on the measuring tool.

Determine what direction the scale should be read. If the ratio is located on the left, read the scale from left to right or right to left if it is located on the right.

Align the start of the object to be measured with the zero mark on the appropriate side of the scale. Find the end of the object and its corresponding line on the scale.

Use the marks and number labels to determine the scaled dimension. For example, a measurement located at the third millimeter mark of a “1:5” scale would be equal to 15 millimeters. A measurement located at the first centimeter mark on a “1:100” scale would be equal to 100 centimeters or 1 meter.