How to Read a Blueprint

Knowing how to read a blueprint is a valuable skill for anyone who works in construction, maintenance, or facilities management. Accurate blueprint reading helps you identify the location of important building elements during renovations, rebuilding, or work on electrical and HVAC systems. And while blueprint symbols can look confusing and intimidating at first, they offer a logical approach that can be quickly mastered with an appropriate blueprint reading seminar

What is a blueprint?

A blueprint is a two-dimensional drawing (or more often, a set of drawings) that provides a visual representation of a building’s layout, dimensions, component placement, electrical wiring, and construction materials. Usually, drawn up by architects, blueprints allow you to quickly check and identify different building elements and verify compliance with building codes

How to read a blueprint

When learning how to read a blueprint, bear in mind that each follows a set of carefully thought out, logical steps. Drawing pages in blueprint sets are arranged in a predictable fashion, and blueprint symbols and lines have highly specific meanings. To prepare for blueprint reading, take the following steps: 

Begin with the title block: The first sheet of a blueprint set is the title block, which includes basic information such as the project name, the drawing date, the architect's contact information, the construction company’s name, and any relevant government approval data. 

The title block also includes the plan index, a handy reference guide listing all the drawings in the blueprint set, and the plan legend, which defines the blueprint symbols used in the drawings. In most cases, these symbols will follow an industry standard (see the blueprint lines section below), but sometimes architects use custom symbols which will be explained in the plan legend. 

Changes to the original blueprints may be listed in the title block, or in the top right corner of relevant blueprint drawings. Drawings include the scale of the blueprint, and an arrow indicating the orientation of the structure. Pay special attention to any architect notes you find, which may be written directly on drawings or included on a separate drawing page. 

Types of blueprint drawings

Blueprints come in three major varieties: plan view drawings, elevation view drawings, and section view drawings. 

  • Plan view drawings are what most people visualize when they think of building blueprints: a horizontal, bird’s-eye view of the building, with a plan, view drawing for each floor of the structure (including foundations, basements, and rooftops).
  • Elevation view blueprints are drawn on a vertical plane and are often used to show the appearance of the exterior of a building (some elevation views depict the interior building elements).
  • Section views, like elevation views, are drawn on the vertical plane and duplicate the inside of a section of the building, revealing the location of insulation, wall studs, wiring, and other elements.

Understanding blueprint pages

Blueprints often come in sets, especially for large, complex structures. In order to keep blueprint sets organized, a standard set of letter codes is combined with page numbers to describe the objective of each drawing and its place in the set. Letter codes include: 

  • G: General sheets such as the cover sheet, the plan index, the title block, and plot plans.
  • A: Architectural plans for walls, roofs, ceilings, floors, and building sections. 
  • S: Structural engineering blueprints including outlines for the building foundation, framing plans, and roof structure. 
  • E: Electrical plans outlined the location and function of electric fixtures, outlets, pictures, panel boxes, etc. 
  • M: Mechanical plans concerning the building’s HVAC system, ductwork, piping, control wiring, etc. 
  • P: Plumbing sheets.

Also included in blueprint drawings are door, window, and finish schedules, which provide information on the size, style, and materials used for doors, windows, and other finishes. Blueprint sets will also include specification sheets, which offer in-depth descriptions of all materials used during construction. 

Reading blueprint symbols

The most daunting aspect of blueprint reading is deciphering the many lines that make up the drawing. Practice, ideally backed up with some formal blueprint reading training, will help you learn what each type of line means. If you need any help understanding blueprint symbols, here’s a quick cheat sheet covering the most common lines found in blueprint drawings:

Blueprint symbols



Object line

Indicates the sides of a building element that would be visible to a real-life observer.

Completely solid, and the thickest lines found on a blueprint.

Hidden lines

Reveals building object surfaces hidden from view when seen in person. 

Short dashes that are half the width of object lines.

Center lines

Used to indicate the central axis of a building element. 

Alternating long and short dashes the same width as hidden lines. 

Dimension lines

Shows the distance between two points on the blueprint.

Two solid lines with arrowheads pointing in opposite directions. Dimension information is written in the gap between the lines. 

Extension lines

Paired with dimension lines to show the limit of the building element’s dimensions.

Short solid lines found at the end of dimension lines. 

Leader line

Used to connect a note, number, or other written information to the corresponding building element.

Finely drawn line, often with an arrowhead pointing to the specific building element. 

Phantom line

Used to show how a building element can be moved to alternate locations. Also used to show an object’s adjacent features.

Lone dashes alternated with two short dashes. 

Cutting-plane line

Used to display interior features of a building element.

U-shaped lines with arrows at each end, bisecting the relevant building element. 

Break lines

Used to conserve drawing space by shortening the length of a long, uniform building element.

Short break lines are thick, solid wavy lines drawn freehand, while longer break lines are drawn with rulers and interspersed with hand-drawn zig-zags.

Blueprint drawing training 

While we hope this article has improved your blueprint reading skills, training is important for anyone who needs to really master their understanding of blueprint symbols. TPC Training’s Blueprint Reading Course covers all types of industrial plant blueprints, including hydraulic, pneumatic, piping, plumbing, electrical, air-conditioning, and refrigeration drawings. Course participants learn how to decipher industrial blueprints quickly, effectively, and most importantly, accurately.


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