How To Read Welding Blueprints [Incl. Pictures]

Welding blueprints consist of diagrams, letters and numbers. The diagrams show the type of weld or joint, the numbers represent angles and the letters all have their own meaning

Understanding these symbols is key to creating a weld exactly as it has been designed. While blueprints may look very complicated, they are actually quite straightforward once you know what you are looking at.

When you look at welding blueprints, you will see views of the front, top and right side, and these have a number of symbols. These symbols are key to knowing how to create the weld.

Here we’ll take a look at some of the markings you will see and what they mean.

The first thing you need to check is the type of joint you will be welding. These are pretty easy to read and understand.

Basic symbols

Welding symbols are attached to a horizontal line with an arrow leading off it. This line is called the reference line and the arrow will point to where the weld should be made.

The reference line will have other symbols, and this is where things get more complicated. The first thing you need to be able to do, is recognise the symbols and what they mean. Thankfully the shape of the symbol often represents the name of the weld or groove, so a V would indicate a V weld.

The placement of the symbol on the reference line is very important.

  • Below: If the symbol is written underneath the reference line, this signifies that the weld should be made on the side of the arrow.
  • Above: If the symbol is written above the reference line, the weld should be made on the opposite side from where the arrow is pointing.
  • Both sides: If the symbol is on both sides of the line, then you will need to weld on both sides of the joint.

Having checked where to make the weld, and which weld you need, there are other symbols you then need to recognise. These will tell you more about how to actually make the weld. For example, whether to weld around the joint, or allow the filler to melt in.

As well as symbols, you will also see letters on the blueprints.

A: Angle Of Countersink

C: Chipping Finish

F: Finishing Symbol

G: Grinding Finish

L: Length of Weld

M: Machining Finish

N: Number of spot welds or projection welds

P: Pitch of welds (center-to-center spacing)

R: Root Opening; Depth of Filling

S: Depth of Preparation; Size of Strength

T: Specification Process

Dimensions and Angles

Now you can understand the reference line, leader line, arrow and weld type, you need to understand what the numbers on the blueprints mean.

  • The number on the left denotes the diameter of the weld, and this is expressed as a fraction of an inch.
  • The number of the right indicates the length of the weld in inches.

If the number is below the refence line, these refer to the joint on the side of the arrow

If the number is above the reference line, these apply to the joint on the opposite side.


This graphic courtesy of the American Welding Society, gives a better idea of how a weld will be shown and what each symbol means. There is a lot to remember with even the smallest weld, so always make sure you know what each symbol means and how it is interpreted in to your weld.

Other Information

Welding blueprints also have other information on them.

  • Materials: You will see a section on the blueprint which lists the materials used, the parts needed and provides any explanatory notes that you will need.
  • Revisions: There is also a section called revisions, which will have information about any revisions you need to consider.

Frequently Asked Questions:

Do you need to be able to read blueprints to weld?

You don’t have to be able to read blueprints, but it can help if you want a career in welding. Many welders learn on the job and will know from experience how to complete most welds. However, if you plan to weld in the engineering field, you will need to understand blueprints, as they are vital for the overall project.

How can you learn to read blueprints?

Reading welding blueprints is something you need to be taught properly. You could learn on your own, but if you are experienced in welding, you may be tempted to cut corners. There are courses available to teach welders how to correctly read and apply blueprints. There are also welders who will provide training on site.

How important are blueprints?

For hobbyists and DIYers, they’re not really important. Welders who carry out smaller welds, can also usually work out for themselves what they need to do. For larger engineering projects, however, they are vital. Each weld is carefully calculated and measured, and the slightest mistake in a weld can have consequences on the rest of the build.


Many welders will never see or use blueprints, but it can still be useful to understand some of the basic symbols.

If you are an occasional welder, then you won’t need any information but if you want to progress in welding, you will need to be prepared to learn and obtain certifications as you go. Understanding blueprints is just one part of a welder’s training, but it is a very important one for many projects.

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