What Are the ASME Y14.5 and ASME Y14.100 Standards?

Engineering drawing adhering to dimensioning and tolerancing in ASME Y14.5-2018 and ASME Y14.1-2020.

An aerial view plan of a Babylonian castle from 2000 B.C. is the oldest recorded history of engineering drafting. With computer aided design as well as standardization for engineering drawings, engineers today have been made tremendously more capable than engineers of the past. ASME Y14.5-2018 and ASME Y14.1-2020 establish uniform practices for stating and interpreting dimensioning, tolerancing, and related requirements for use on engineering drawings— a subcategory of technical drawings that show the shape, structure, dimensions, tolerances, accuracy, and other requirements needed to manufacture a product or part.  

Why Do Engineers Need to Know How to Draw?

Engineers need to understand engineering drawings (also known as technical diagrams, blue prints, prints, mechanical or manufacturing drawings, or schematics) to effectively understand project development, outcomes, and functions. This means engineers should know how to draw products—such as roads, bridges, buildings, dams, thermal or mechanical device—they work on to accurately communicate building instructions to manufacturers.

Additionally, engineer drawings are useful for the building process because they help project managers estimate how much material is necessary and how to plan the steps for completing a project. With computer aided design (CAD) software, engineers can make these drawings digitally. Engineers thereby can modify and optimize their highly-detailed and industry specific design in the construction and development process. Drawing technicians may specialize, for instance, in electric or electronic, mechanical, aerospace, interior design, architectural, or civil engineering drawings.

What Is ASME Y14.5-2018?

ASME Y14.5-2018 establishes symbols, rules, definitions, requirements, defaults, and recommended practices for stating and interpreting dimensioning and tolerancing. It also provides requirements for use on engineering drawings, models defined in digital data files, and related documents. ASME Y14.5.1M provides a mathematical explanation of the principles in ASME Y14.5-2018, and ASME Y14.41 defines more uniform practices for applying dimensions, tolerances, and related requirements in digital data sets.

Practices unique to architectural and civil engineering and welding symbology are not included in this standard.

Architect using computer aided design (CAD) program that adheres to ASME Y14.5-2018 and ASME Y14.1-2020.

What Are Dimensioning and Tolerancing?

Due to variations in the manufacturing processes, manufactured items differ in size and dimensions from the original computer aided design (CAD) model. Geometric Dimensioning and Tolerancing (GD&T) tells manufacturing partners and inspectors the allowable variation within the product assembly and standardizes how to measure that variation. To optimally control and communicate these variations, engineers and manufacturers use a symbolic language: GD&T.


Dimensions are numerical values or mathematical expressions in appropriate units of measure used to define the shape, size, orientation, or location of a part feature or between part features. They may be applied by means of dimension lines, extension lines, chain lines, notes, or leaders from dimensions; dimensions can be applied through specifications directed to the appropriate features or contained in a digital data set. Here are the types of dimensioning specified in ASME Y14.5-2018:

  1. Millimeter Dimensioning
  2. Decimal Inch Dimensioning
  3. Decimal Points
  4. Default for Conversion and Rounding of Linear Units


Tolerance is the total amount a dimension or feature is permitted to vary. The tolerance is the difference between the maximum and minimum lines. Here are the types of tolerancing specified in ASME Y14.5-2018 for expressing tolerances on linear or angular dimensions:

  1. Millimeter Tolerances
  2. Inch Tolerances
  3. Angle Tolerances
Dimensional tolerancing depicted in engineering drawing.

What Is ASME Y14.1-2020?

ASME Y14.1-2020 defines decimal inch sheet sizes and formats for engineering drawings. Both metric and decimal-inch sheet sizes and formats are included in the standard. For engineering product definition preparation and practices, see ASME Y14.41. The objective of ASME Y14.1-2020 is to provide uniformity of drawing sizes and the location of format features on all engineering drawings. For example, line width, sizes of blocks, and size and style of lettering should be in accordance to ASME Y14.2, and dimensioning and tolerancing should be in accordance with ASME Y14.5-2018. Adhering to uniformity thereby provides advantages in readability, handling, filing, and reproduction.

History of Computer Aided Design (CAD)

Before today’s modern age, engineering drafting meant skilled designers were hand drawing the curves, arc, and circles in plans with a straight-edge, triangles, T-square, protractor, or compass—a tediously time-consuming task. In 1963, Ivan Sutherland invented a program called Sketchpad, which was the first graphically interfaced computer aided design (CAD) program, allowing users to create x-y plots. Engineers at Boeing, Ford, Citroen, MIT, and GM made significant investments in CAD programs in the 1960s. In 1982, the first version of AutoCAD, a CAD and drafting software application by Autodesk, began with the release of version 1.0. However, at this time, the computer hardware available was holding CAD programs back.

It was not until the late 1980s and early 1990s that CAD software became capable enough to be practical in engineering design. Leading CAD programs at this time functioned in 2D. It was not until the mid to late 1990s that 3D CAD software was released and grew exponentially in the CAD market.

CAD as a tool has dramatically advanced the field of engineering, bringing the engineering design process into reality. It has allowed engineers to create realistic-looking parts on computer screens with ease and quickly render these parts or assemblies to their near-final appearance while adhering to the uniformity specifications for engineering drawing in the ASME Y14 series.

ASME Y14.5-2018: Dimensioning And Tolerancing and ASME Y14.1-2020: Drawing Sheet Size And Format are available on the ANSI Webstore.

Both standards are also available together in the ASME Y14.5 and ASME Y14.100 Dimensioning Tolerancing and Engineering Drawing Practices Package.

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