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Steel Flange Dimensions Reference
A flange is a stack of dimensions. Get any one of them wrong and the joint either will not bolt up or will not seal. ASME B16.5 and B16.47 do the heavy lifting for forged steel flanges. AWWA C207 handles the plate-cut large diameter end. Below is an orientation to what those tables contain and the steel-specific traps that catch first-time buyers.
What a Dimension Table Contains
Every standardized steel flange table presents the same family of dimensions. Outside diameter sets the physical footprint and determines whether the part will clear adjacent piping, supports, and equipment nozzles. Bolt circle diameter dictates where the studs land relative to that outside diameter and is the single most common interchange criterion when an engineer is checking whether a flange will bolt up to a mating part.
Bolt count and bolt hole diameter combine with bolt circle to define the bolting pattern. The bolt holes are straddle drilled, meaning they sit symmetrically across the principal horizontal and vertical centerlines of the flange face. Hub dimensions cover length through hub, hub diameter at the base, hub diameter at the point of welding, and the small end bore that matches the pipe schedule the flange will be welded to.
Raised face dimensions add face height above the back of the flange and face diameter. Both affect gasket selection and stud length. For ring joint flanges the raised face is replaced by an octagonal or oval groove. The groove number indexes into a ring gasket table on both sides of the joint.
ASME B16.5: 1/2 inch through 24 inch
B16.5 is the dominant flange standard for steel piping in the small and mid-bore range. The standard covers seven pressure classes: 150, 300, 400, 600, 900, 1500, and 2500. Class 150 and 300 cover the bulk of general process service. Class 600 and above appear in high-pressure refinery and chemical work. Below is an illustrative subset of Class 150 and Class 300 weld neck dimensions in steel.
Class 150 Weld Neck (steel)
| Size | OD | BC | Bolts |
|---|---|---|---|
| 2 in | 6.00 | 4.75 | 4 x 5/8 |
| 4 in | 9.00 | 7.50 | 8 x 5/8 |
| 6 in | 11.00 | 9.50 | 8 x 3/4 |
| 8 in | 13.50 | 11.75 | 8 x 3/4 |
| 12 in | 19.00 | 17.00 | 12 x 7/8 |
| 24 in | 32.00 | 29.50 | 20 x 1-1/4 |
Class 300 Weld Neck (steel)
| Size | OD | BC | Bolts |
|---|---|---|---|
| 2 in | 6.50 | 5.00 | 8 x 5/8 |
| 4 in | 10.00 | 7.88 | 8 x 3/4 |
| 6 in | 12.50 | 10.62 | 12 x 3/4 |
| 8 in | 15.00 | 13.00 | 12 x 7/8 |
| 12 in | 20.50 | 17.75 | 16 x 1-1/4 |
ASME B16.47: 26 inch through 60 inch
B16.47 picks up where B16.5 ends, covering nominal pipe sizes 26 inch through 60 inch. The standard splits into two series. Series A is the heavier MSS SP-44 derived pattern, common in transmission pipeline and high-pressure service. Series B is lighter, derived from API 605, and shows up in lower-pressure applications and refinery work where weight savings matter.
The two series are not interchangeable. A Series A flange has a larger outside diameter and a different bolt pattern than the Series B flange of the same nominal size and class. Specifying B16.47 without calling out the series is a recipe for a mismatched joint at the field connection. Bid documents must include the series designation.
Class coverage in B16.47 runs 75, 150, 300, 400, 600, and 900. Class 75 is rarely encountered in current work. Class 150 through 900 covers the production range. For sizes above 60 inch the flange moves to AWWA C207 dimensions or to custom plate-cut work outside any published standard.
AWWA C207: 4 inch through 144 inch Plate-Cut
AWWA C207 covers plate-cut steel flanges for waterworks and large diameter service. The Class B, D, E, and F families top out at 86, 175, 275, and 300 psi respectively. The dimensional importance is that Class B and D share their outside diameter, bolt circle, bolt count, and bolt hole size with ANSI B16.1 Class 125 cast iron and, in most sizes, with the ANSI B16.5 Class 150 pattern.
What does not transfer is the working pressure. A Class B flange at 86 psi looks identical to a Class 125 cast iron flange on the bolt side, but it is not rated for the same service. Always confirm the class stamping and the project specification before assuming interchangeability.
Steel-Specific Dimensional Notes
Raised face height changes with class. Class 150 and 300 steel flanges have a 1/16 inch raised face by default. Class 600 and higher have a 1/4 inch raised face. When that detail is missed, the stud length and gasket compression calculations both come out wrong. The studs ship short. The joint does not seal.
Forged steel flanges have a hub dimension that depends on the pipe schedule the flange welds to. The bore on a Class 600 weld neck for Schedule 80 pipe is not the same as the bore for Schedule 40 in the same nominal size. The order has to specify the schedule, or the default is Schedule 40 (or Standard for sizes 12 inch and below).
Plate-cut flanges in steel do not have a forged hub. The hub, where present, is welded on as a separate component. That difference matters for the QA package: forged flanges carry integral hub MTRs; plate-cut flanges with welded hubs carry separate certifications for the ring and the hub plus a welding procedure qualification record.
Lightweight Class 125LW flanges intended for valve bodies and pump casings share the bolt pattern with Class 150 but are dimensionally lighter through the hub and face. They are not rated for the same piping service and should not be substituted without engineering review.
Working Tools and Drawings
For a full dimensional lookup at any size and class combination, use our calculator. For PDF and CAD drawings of the specific flange you need, see the CAD drawings page.
Need a Dimension Confirmed?
Call (281) 484-8325 or email sales@texasflange.com with the size, class, and facing. We will confirm against our stock and send the dimensional drawing for review.
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