Pipe Flange Dimensions (with Drawings)

Stacy Randall
by Stacy Randall

A flange, by definition, is a projecting part that connects, strengthens, and stabilizes sections of piping or machinery. In pipefitting, there are a great variety of pipe flanges that serve different functions and work with different substances. Flanges help expedite maintenance operations, as they are more easily and quickly disassembled than welded connections.

It is extremely important to match the correct flange to the materials and processes being performed. Pipe flanges range in size and thickness depending on the pipes connected and the flow pressure. The most commonly used pipe flange for ½-inch piping measures 2.83 inches in outside diameter.

While pipe flanges are primarily functional parts, they are also used for decorative purposes as well. Industrial decor features pipes and connectors as exposed elements or as bracketing for shelves or room dividers. In this case, both size and material are significant factors in the overall aesthetic.

Source: Amazon

What Are the Different Types of Pipe Flanges?

Weld Neck Pipe Flange

Weld neck flanges resemble a short stovepipe, featuring a weld bevel and a neck extension that slips over the pipe. They are most common in high-temperature and high-pressure setups with multiple bends and provide a natural form connection between pipes. Their diameters measure 3.88 inches for ¾-inch pipes, and 4.25 inches for ½-inch IPS galvanized pipes.

For copper piping, the weld neck flange’s circular base has a 1.05-inch diameter and runs .44 inches thick. The neck extension’s diameter measures 1.05 inches across and extends 2 inches high.

Galvanized pipe flanges have an outside diameter of 3.88 inches and an inside diameter of .84 inches. They are 1.41 inches tall.

Socket Weld or Counter Bore Flange

Socket weld or counter bore flanges have a shorter raised lip around the inside diameter where the pipe fits through. The flanges for ½-inch piping have a .88 inch inside diameter and a 3.5 inch outside diameter. Additionally, ¾-inch pipework flanges measure 1.09 inches in inside diameter and 3.88 inches in outside diameter.

Socket weld flanges are ideal for low-temperature and low-pressure setups, space limitations, and smaller-sized high-pressure systems. Socket weld flanges attach to pipes by inserting the pipe and securing with fillet weld around the top. This attachment creates a smoother bore and a better flow through the piping.

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Slip-On Pipe Flange

Slip-on flanges look similar to socket weld flanges, with the difference being the method they secure to the piping. The flange slips onto the pipe the same way, but the welding occurs around both the inner and outer diameters. Though this installation method is slightly more technical, this flange allows for higher flow rates and capacity.

Slip-on flanges for ½-inch piping measure a 0.88″ inch interior diameter and a 3.5 inches exterior diameter. Likewise, ¾-inch piping couples with flanges of 1.09 inch inside diameter and 3.88″ inch outside diameter. Benefits of using slip-on flanges include low-cost installation, easier alignment, and a stronger welding hold.

Source: Amazon

Blind Pipe Flange

A blind flange caps off a pipe’s end flow, acting as a “lid” with bolt holes to seal the opening. Unlike the other flange types, the blind flange has no center hole to slip over a pipe. Because of this, it has no inner diameter measurement; its diameter for a ¾-inch copper pipe measures 1 inch.

Blind flanges have a flush or slightly raised center cap where the pipe opening would typically be. This raised center measures ⅛ inch high, with the remaining dimensions being 1 inch high by 1 inch thick. When used with a suitable gasket, the blind flange provides a tight but easily removed seal.

Threaded or Companion Pipe Flange

Threaded or companion flanges are the easiest for the average layperson to install. They have a female NPT threaded center that screws onto a matching male threaded pipe. So while a weld seal is doable for extra hold, the threaded connection makes it unnecessary.

Threaded flanges are circular with a small raised lip at the inside diameter measuring ⅛ inch to ¼ inch high. A ½-inch pipe flange measures 2.38 inches and 3.5 inches for the inside and outside diameters, respectively. Likewise, ¾-inch pipe flanges measure 2 ¾ inches for an inside diameter and 3 ⅞ inches for the outer diameter.

Lap Joint Flange

Lap joint flanges resemble weld neck flanges with their stovepipe-like design, but lap joint flanges are a two-part assembly. It consists of a stub end assembly that slips over the pipe and a ring that fits around its base. The stub end welds to the pipe, and the flange ring rotates to align with it.

Lap joint flanges are perfect for systems with limited physical space or require frequent disassembly and maintenance. Fittings for ½-inch piping measure 2 ⅜ inches for the inside diameter and 3 ½ inches for the outside diameter. Fittings for ¾-inch piping measure 2 ¼ inches for the inside diameter and 3 ⅞ inches for the outside diameter.

Split Flange

Sometimes you may need a specialty or custom fabricated flange that replaces or enhances an existing flange or pre-existing piping. There are a few types, but one especially suited to home use is the split flange. A split flange consists of two interlocking pieces that connect with either welding or nuts and bolts.

Dimensions for an average-sized split flange have a 2.83-inch outer diameter and a .85 inch center diameter. They are made to fit securely around ½-inch IPS galvanized pipe or ¾-inch copper pipe. The split flange is typically flat with a flat, rimless center hole.

A good instance for using a split flange is connecting pipes in a hard-to-reach location. Instead of dismantling the assembly for replacement, you can separate the split flange to slip over the existing pipe. You can also use them to reinforce a weakened area of pipe or add an attachment.

Source: Amazon

Sink Flanges

A sink flange is the most commonly seen flange in any given household. It is the opening that connects to the sink drain through the basin opening. A sink flange can also feature a drain stopper or mesh strainer basket for easier drainage.

Sink flanges come in different sizes, with bathroom sink flanges being smaller than kitchen sink flanges. Bathroom sink flanges measure 1 ¼ inch in diameter, and kitchen sink flanges are universal, measuring 3 ½ in diameter. Incidentally, today’s standard shower drain flange is the same diameter as the kitchen sink.

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Decorative Flanges

Industrial and steampunk design give pipe flanges the opportunity to blend substance with style and form with function. Decorative flanges are not rated to carry gas or water, but they do outfit furniture and support open shelving. Decorative flanges come in a variety of metal finishes and etched designs.

In addition to round designs, decorative flanges are also available in square shapes. Their diameters are smaller than serviceable pipe flanges, measuring 2.5 inches in outside diameter.

Square flanges can measure from 1×1 inch to 3×3 inches, with ½-inch or 1 inch inside diameters.

How To Measure for Pipe Fittings

When measuring for pipe fittings, for male threads, measure the outside diameter of the pipe. Conversely, for female threads, measure the inner diameter of the pipe.

For male threads, wrap a piece of string around the pipe and mark it where it touches. Then lay out the string and measure from the tip to the mark you made. This is the pipe’s circumference. Divide it by pi, 3.14159, to get the diameter.

For female threads, use a tape measure to measure the inside diameter of the pipe. For either thread, take the resulting decimal figure or diameter and use the chart to find the pipe size.

DiameterEquivalent DecimalPipe Size

Related Questions

How do I properly size a flange for pipe use?

Properly sizing a flange for pipe use depends not only on the type of flange but its compatible piping. The pipe must slip into the flange’s inside diameter easily and securely, and the outside diameter should cover wall holes. Once you determine the specific flange type and material you need for the job, you’ll need to take several measurements.The four measurements you’ll need are the inside diameter, outside diameter, bolt hole count, and bolt hole center. You’ll need to align each of these measurements from opposing bolt holes to get the most accurate readings. Take all measurements from edge to edge and try to get as precise as possible to match the correct product.Round up bolt diameter to the next half or whole step since bolts measure half or whole inches. Once you have all four measurements, check them against the manufacturer’s table to find the correct flange. Most manufacturers list these specifications on their websites for easy reference.

What are the three parts of a flanged connection?

Pipe flanges, gaskets, and bolts are the three parts that comprise a flanged connection. Gaskets and bolts are typically made of the same flange materials or a material approved for the pipe components. Each component comes in various materials that suit specific applications and must be matched correctly for proper functioning.The gaskets come in two conventional types: full-face gaskets and ring gaskets. Full-face gaskets have the bolt holes visible and pair up with raised-face gaskets. Ring gaskets tend to be smaller rings minus the bolt holes and pair up with flat-faced flanges.Securing the flange components requires matching the surfaces evenly and plumb, adjusting as needed for a uniform fit. Once all surfaces match, bring the flanges together and secure at least two of the bolts. Refine the alignment, so the remaining bolt holes match and their corresponding bolts are tightly secured.

Stacy Randall
Stacy Randall

Stacy Randall is a wife, mother, and freelance writer from NOLA that has always had a love for DIY projects, home organization, and making spaces beautiful. Together with her husband, she has been spending the last several years lovingly renovating her grandparent's former home, making it their own and learning a lot about life along the way.

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