01
Weld Neck Flange
ASME B16.5 Class 300 Flange Dimensions
02
Threaded Flange
03
Slip On Flange
04
Lap Joint Flange
05
Socket Weld Flange
06
Blind Flange
Texas Flange publishes the full ASME B16.5 Class 300 (300#) flange dimensions below, for every nominal size from 1/2" through 24". A 4" Class 300 flange, for example, has a 10.00" outside diameter and eight 0.88" bolt holes on a 7.88" bolt circle. Texas Flange has been providing ASME B16.5 (ANSI) Class 300 flanges since 1986. For drawings, see our CAD and 3D flange drawings, or contact us for a quote.
Published by Texas Flange, Pearland, Texas. Dimensions per ASME B16.5. Last reviewed October 6, 2026.
Class 300 (300#) flange dimensions, ASME B16.5, in inches
| Nom. Pipe Size | O | T | TJ | R | X | #/Dia of Holesa | Bolt Circle Dia | B | B2b | B3 | H | L | L2 | L3c | r | C | D | Thr |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ½ | 3.75 | 0.50 | 0.56 | 1.38 | 1.50 | 4-0.63 | 2.62 | 0.88 | 0.62 | 0.90 | 0.84 | 0.81 | 2.00 | 0.88 | 0.12 | 0.93 | 0.38 | 0.62 |
| ¾ | 4.62 | 0.56 | 0.62 | 1.69 | 1.88 | 4-0.75 | 3.25 | 1.09 | 0.82 | 1.11 | 1.05 | 0.94 | 2.19 | 1.00 | 0.12 | 1.14 | 0.44 | 0.62 |
| 1 | 4.88 | 0.62 | 0.69 | 2.00 | 2.12 | 4-0.75 | 3.50 | 1.36 | 1.05 | 1.38 | 1.32 | 1.00 | 2.38 | 1.06 | 0.12 | 1.41 | 0.50 | 0.69 |
| 1¼ | 5.25 | 0.69 | 0.75 | 2.50 | 2.50 | 4-0.75 | 3.88 | 1.70 | 1.38 | 1.72 | 1.66 | 1.00 | 2.50 | 1.06 | 0.19 | 1.75 | 0.56 | 0.81 |
| 1½ | 6.12 | 0.75 | 0.81 | 2.88 | 2.75 | 4-0.88 | 4.50 | 1.95 | 1.61 | 1.97 | 1.90 | 1.13 | 2.63 | 1.19 | 0.25 | 1.98 | 0.62 | 0.88 |
| 2 | 6.50 | 0.81 | 0.88 | 3.62 | 3.31 | 8-0.75 | 5.00 | 2.44 | 2.07 | 2.46 | 2.38 | 1.25 | 2.69 | 1.31 | 0.31 | 2.50 | 0.69 | 1.12 |
| 2½ | 7.50 | 0.94 | 1.00 | 4.12 | 3.94 | 8-0.88 | 5.88 | 2.94 | 2.47 | 2.97 | 2.88 | 1.44 | 2.94 | 1.50 | 0.31 | 3.00 | 0.75 | 1.25 |
| 3 | 8.25 | 1.06 | 1.12 | 5.00 | 4.62 | 8-0.88 | 6.62 | 3.57 | 3.07 | 3.60 | 3.50 | 1.63 | 3.06 | 1.69 | 0.38 | 3.63 | 0.81 | 1.25 |
| 3½ | 9.00 | 1.12 | 1.19 | 5.50 | 5.25 | 8-0.88 | 7.25 | 4.07 | 3.55 | 4.10 | 4.00 | 1.69 | 3.13 | 1.75 | 0.38 | 4.13 | …. | 1.44 |
| 4 | 10.00 | 1.19 | 1.25 | 6.19 | 5.75 | 8-0.88 | 7.88 | 4.57 | 4.03 | 4.60 | 4.50 | 1.82 | 3.32 | 1.88 | 0.44 | 4.63 | …. | 1.44 |
| 5 | 11.00 | 1.31 | 1.38 | 7.31 | 7.00 | 8-0.88 | 9.25 | 5.66 | 5.05 | 5.69 | 5.56 | 1.94 | 3.82 | 2.00 | 0.44 | 5.69 | …. | 1.69 |
| 6 | 12.50 | 1.38 | 1.44 | 8.50 | 8.12 | 12-0.88 | 10.62 | 6.72 | 6.07 | 6.75 | 6.63 | 2.00 | 3.82 | 2.06 | 0.50 | 6.75 | …. | 1.81 |
| 8 | 15.00 | 1.56 | 1.62 | 10.62 | 10.25 | 12-1.00 | 13.00 | 8.72 | 7.98 | 8.75 | 8.63 | 2.38 | 4.32 | 2.44 | 0.50 | 8.75 | …. | 2.00 |
| 10 | 17.50 | 1.81 | 1.88 | 12.75 | 12.62 | 16-1.12 | 15.25 | 10.88 | 10.02 | 10.92 | 10.75 | 2.56 | 4.56 | 3.75 | 0.50 | 10.88 | …. | 2.19 |
| 12 | 20.50 | 1.94 | 2.00 | 15.00 | 14.75 | 16-1.25 | 17.75 | 12.88 | 12.00 | 12.92 | 12.75 | 2.82 | 5.06 | 4.00 | 0.50 | 12.94 | …. | 2.38 |
| 14 | 23.00 | 2.06 | 2.12 | 16.25 | 16.75 | 20-1.25 | 20.25 | 14.14 | 13.25 | 14.18 | 14.00 | 2.94 | 5.56 | 4.38 | 0.50 | 14.19 | …. | 2.50 |
| 16 | 25.50 | 2.19 | 2.25 | 18.50 | 19.00 | 20-1.38 | 22.50 | 16.16 | 15.25 | 16.19 | 16.00 | 3.19 | 5.69 | 4.75 | 0.50 | 16.19 | …. | 2.69 |
| 18 | 28.00 | 2.31 | 2.38 | 21.00 | 21.00 | 24-1.38 | 24.75 | 18.18 | 17.25 | 18.20 | 18.00 | 3.44 | 6.19 | 5.12 | 0.50 | 18.19 | …. | 2.75 |
| 20 | 30.50 | 2.44 | 2.50 | 23.00 | 23.12 | 24-1.38 | 27.00 | 20.20 | 19.25 | 20.25 | 20.00 | 3.69 | 6.32 | 5.50 | 0.50 | 20.19 | …. | 2.88 |
| 22 | 33.00 | 2.57 | 2.63 | 25.25 | 25.25 | 24-1.63 | 29.25 | 22.22 | 21.25 | 22.25 | 22.00 | 3.93 | 6.43 | 5.75 | 0.50 | 22.19 | …. | 3.13 |
| 24 | 36.00 | 2.69 | 2.75 | 27.25 | 27.62 | 24-1.63 | 32.00 | 24.25 | 23.25 | 24.25 | 24.00 | 4.13 | 6.56 | 6.00 | 0.50 | 24.19 | …. | 3.25 |
Dimensions are in inches.
(a)- Bolt hole diameter 1/8 in. larger than bolt diameter. (b)- Standard bore dimensions provided. See bore chart for other wall thicknesses. (c)- This dimension is commonly associated with “true” lap joints. Industry standard is to make to the slip on length through the hub.
Frequently Asked Questions
- What pressure can a Class 300 flange handle?
- An ASME B16.5 Class 300 flange in A105 carbon steel is rated to 740 psi at 100°F. The "300" is a class designation, not the working pressure, and the rating falls as temperature rises, to 605 psig at 500°F (ASME B16.5-2025, Material Group 1.1). Always confirm the pressure-temperature rating for your specific material grade.
- What sizes do Class 300 flanges come in?
- ASME B16.5 covers Class 300 flanges from NPS ½" through 24", and every one of those sizes is in the table on this page. Above 24", the equivalent standard is ASME B16.47 Series A and B. See the Class 300 Series A dimension table.
- What is the difference between Class 150 and Class 300 flanges?
- Class 300 is rated to 740 psi at 100°F in A105 against 285 psi for Class 150, and it gets there with a thicker, heavier flange on a larger bolt circle. A 4" Class 300 flange is 10.00" outside diameter with eight 0.88" holes on a 7.88" bolt circle; the same size in Class 150 is 9.00" outside diameter with eight 0.75" holes on a 7.50" bolt circle. The bolt patterns are not interchangeable. See the Class 150 dimension table to compare size by size.
- How many bolts does a Class 300 flange use?
- It depends on the size. ASME B16.5 bolt-hole counts are always a multiple of four, running from 4 bolts on ½" through 1½" up to 24 bolts of 1-1/2" diameter, in 1.63" holes, on a 32.00" bolt circle at 24". The exact count, hole diameter and bolt circle for every size are in the Class 300 table on this page, and bolt and stud sizes are on the Texas Flange bolt chart.
- What flange types are available in Class 300?
- Class 300 is available in every ASME B16.5 type Texas Flange produces: weld neck, slip-on, blind, threaded, socket weld, and lap joint, in raised face (RF) or ring type joint (RTJ).
- What does the # symbol mean in 300# flange?
- The # symbol is shorthand for pressure class, so 300# and Class 300 mean the same thing. It is a class designation, not a weight and not a direct pressure rating. A Class 300 carbon steel flange in Material Group 1.1 is rated to 740 psig at -20 to 100 degrees F, and that rating falls as temperature rises.
- What are the bolt hole dimensions for a Class 300 flange?
- Bolt hole dimensions for an ASME B16.5 Class 300 flange are set by nominal pipe size. Each size specifies a bolt circle diameter, a bolt hole diameter, and a bolt count. A 4 inch Class 300 flange, for example, has 8 holes of 0.88 inch diameter on a 7.88 inch bolt circle, with a 10.00 inch outside diameter. Full bolt hole dimensions for every size from 1/2 inch through 24 inch are in the Class 300 dimension table on this page, and bolt and stud sizes are on the Texas Flange bolt chart.
- What is the difference between Class 300 and Class 600 flanges?
- Class 600 flanges are rated for twice the working pressure of Class 300 at the same temperature. In Material Group 1.1 at -20 to 100 degrees F, Class 300 is rated to 740 psig and Class 600 to 1480 psig. From 1/2 inch through 3-1/2 inch the two classes share the same outside diameter and bolt circle, but Class 600 is thicker (a 2 inch flange is 1.00 inch thick in Class 600 against 0.81 inch in Class 300). From 4 inch up, Class 600 is also larger: a 4 inch Class 600 flange is 10.75 inch outside diameter on an 8.50 inch bolt circle, against 10.00 inch and 7.88 inch in Class 300. See the Class 600 dimension tables.
- Are Class 300 flange dimensions the same as ANSI B16.5 and ASME B16.5?
- Yes. ANSI B16.5 and ASME B16.5 refer to the same standard, so a flange described as ANSI B16.5 Class 300 and one described as ASME B16.5 Class 300 have identical dimensions. ANSI is the accrediting body and ASME publishes the standard. The dimensions on this page apply under either name.
