Flange Weight Calculator

Units

Flange Type

Weld Neck Raised Face

Material

ANSI B16.5 WNRF presets

Outside Diameter

Inside Diameter

Thickness

Hub Base OD

Hub Length

Bolt Holes

Hole Diameter

Quantity

Cost estimate

Price per kg. Total cost = total weight × price per kg.

WNRF Flange · Carbon Steel (ASTM A105)

OD 228.6 mm · 8 bolt holes

Weight per flange

9.361kg

20.638 lb

Weight Breakdown

Dimensions, volume, and material details

Weight per piece

9.361kg

20.638 lb

Total weight

9.36kg

Volume per piece

1,192.49cm³

72.77 in³

Outside diameter

228.6 mm

Inside diameter (bore)

102.3 mm

Thickness

23.9 mm

Bolt holes

8 × Ø19.1 mm

Material density

7850 kg/m³

Formula Used

The exact formula applied for weld neck (wnrf) weight

Weld Neck (WNRF) with hub volume

Weight = [π/4×(OD²−ID²)×t + π/4×(HubOD²−ID²)×HL − n×π/4×d²×t] × ρ × Q

OD = outside diameter · ID = inside diameter · t = thickness · n = bolt holes · d = hole diameter · ρ = density · Q = quantity · HL = hub length

Density (ρ) = 7850 kg/m³ (Carbon Steel (ASTM A105))

What Is a Flange Weight Calculator?

Calculate pipe flange weight in kg or lb for WNRF, SORF, Blind, and other types

A Flange Weight Calculator is an engineering tool that computes the theoretical weight of pipe flanges from their geometric dimensions and material density. It accounts for the flange body (ring or solid disc), the hub section on weld neck flanges, and subtracts material removed by bolt holes — giving precise weight estimates used by piping engineers, procurement teams, steel traders, and fabricators for material ordering, freight estimation, and structural load calculations.

flange types

WNRF, SORF, Blind, Threaded, SW, Lap Joint

materials

MS, SS, Duplex, Hastelloy, Inconel, Titanium…

ANSI classes

Class 150, 300 & 600 with standard dims

Flanges are critical components in piping systems, used to connect pipes, valves, pumps, and other equipment. They come in various types — Weld Neck (WNRF) for high-pressure applications, Slip-On (SORF) for lower-pressure systems, Blind (BLRF) to close off ends, and more. Accurate weight calculation is essential because flanges are often priced and shipped by weight. This calculator covers six flange types across nine materials, with ANSI B16.5 presets for instant standard dimension lookup.

How to Calculate Flange Weight

A four-step process from flange type and dimensions to weight

Select Flange Type

Choose from 6 flange types — WNRF, SORF, BLRF, Threaded, Socket Weld, and Lap Joint. Each type has a different geometry that affects weight. WNRF includes a hub volume, blind flanges are solid discs without a bore.

Enter Dimensions

Input the outside diameter (OD), inside diameter (ID/bore), and flange thickness. For WNRF flanges, also enter the hub base OD and hub length. Use ANSI B16.5 presets for standard dimensions (Class 150, 300, 600, ½"–24" NPS).

Add Bolt Holes

Specify the number of bolt holes and hole diameter. The calculator subtracts the material removed by bolt holes from the total volume. Standard bolt patterns are pre-filled when using ANSI presets.

Choose Material & Get Results

Select from 9 materials with built-in densities — Carbon Steel (7,850), SS 304/316 (8,000), Duplex (7,800), Hastelloy (8,940), Inconel (8,440), Monel (8,840), and Titanium (4,510). Toggle between metric (mm/kg) and imperial (in/lb).

Core Formula

Weight = [π/4×(OD²−ID²)×t + Hub − n×π/4×d²×t] × ρ × Q

Where OD = outside diameter, ID = inside diameter (0 for blind flanges), t = thickness, Hub = π/4×(HubOD²−ID²)×HubLength (WNRF only), n = bolt holes, d = hole diameter, ρ = density, Q = quantity. All dimensions in consistent units. Blind flanges use OD² instead of (OD²−ID²).

Worked Example: 4" Class 150 WNRF — Carbon Steel

For a mild steel weld neck flange (ρ = 7,850 kg/m³):

Body = π/4 × (228.6² − 102.3²) × 23.9 = 784,582 mm³
Hub = π/4 × (134.9² − 102.3²) × 76.2 = 462,479 mm³
Bolt holes = 8 × π/4 × 19.1² × 23.9 = −54,779 mm³
Net volume = 784,582 + 462,479 − 54,779 = 1,192,282 mm³
Weight = 1,192,282 × 10⁻⁹ × 7,850 = 9.36 kg

Flange Weight Examples at a Glance

Quick reference for frequently used flange sizes and materials

4" Class 150 WNRF — MS

9.36 kg

20.64 lb per flange

OD 228.6 · ID 102.3 · Th 23.9 · Hub 134.9×76.2 mm

Carbon Steel (7,850 kg/m³) · 8 bolt holes × Ø19.1

4" Class 300 WNRF — SS 304

15.88 kg

35.02 lb per flange

OD 254.0 · ID 102.3 · Th 31.8 · Hub 146.1×85.9 mm

Stainless Steel 304 (8,000 kg/m³) · 8 bolt holes × Ø22.2

4" Class 150 BLRF — MS

7.27 kg

16.03 lb per flange

OD 228.6 · Th 23.9 mm (solid disc, no bore)

Carbon Steel (7,850 kg/m³) · 8 bolt holes × Ø19.1

8" Class 150 WNRF — Titanium

14.31 kg

31.54 lb — 43% lighter than MS

OD 342.9 · ID 202.7 · Th 28.4 · Hub 246.1×101.6 mm

Titanium Grade 2 (4,510 kg/m³) · 8 bolt holes × Ø22.2

Material Density Reference

Standard densities used in flange weight calculations

Material	kg/m³	lb/in³
Carbon Steel (ASTM A105)	7,850	0.284
Stainless Steel 304	8,000	0.289
Stainless Steel 316	8,000	0.289
Duplex Steel (UNS S32205)	7,800	0.282
Alloy Steel (ASTM A182 F11)	7,850	0.284
Hastelloy C276	8,940	0.323
Inconel 600	8,440	0.305
Monel 400	8,840	0.319
Titanium Grade 2	4,510	0.163

Densities shown are typical reference values. Actual density may vary slightly by grade and manufacturing process. Stainless Steel 304 and 316 share the same density (8,000 kg/m³) but have different mechanical properties and corrosion resistance.

Tips for Accurate Flange Weight Calculation

Practical advice for procurement, fabrication, and piping design

Always include hub dimensions for WNRF

The weld neck hub can add 20–40% to the total flange weight. Using only the ring formula without hub volume significantly underestimates WNRF weight.

Use ANSI B16.5 presets for standard flanges

Save time and avoid dimension errors by using the built-in Class 150/300/600 presets. Dimensions follow ASME B16.5 standards for ½" to 24" NPS.

Verify density for exotic alloys

Hastelloy C276 (8,940 kg/m³) is 14% heavier than carbon steel, while Titanium (4,510 kg/m³) is 43% lighter. Selecting the wrong material can lead to significant weight estimation errors.

Account for raised face and gasket groove

ASME B16.5 flanges include a raised face (1.6 mm for Class 150/300, 6.4 mm for Class 400+) that adds marginal weight. For procurement-critical applications, add 1–2% margin.

Common Mistakes When Calculating Flange Weight

Avoid these frequent errors that lead to wrong weight estimates

Forgetting to subtract bolt holes

For large Class 600/900 flanges with 12–20 bolt holes, the removed material can account for 3–5% of total weight. The calculator handles this automatically.

Treating a blind flange like a ring

Blind flanges are solid discs — there is no bore. Using the ring formula (OD² − ID²) for a blind flange underestimates weight by 30–60% since you're subtracting material that doesn't exist.

Confusing flange OD with pipe OD

A 4" NPS flange has an OD of 228.6 mm (Class 150), not 114.3 mm (the pipe OD). Always use the flange outside diameter from the standard, not the nominal pipe size.

Mixing material grades with same density

SS 304 and SS 316 both have 8,000 kg/m³ density, but different mechanical properties and cost. Always specify the correct grade for procurement, even if the weight is identical.

Frequently Asked Questions

Common questions about flange weight calculation, materials, and ANSI standards

Flange weight is calculated using the formula: Weight = Net Volume × Material Density. The net volume is derived from the flange geometry — the body volume (π/4 × (OD² − ID²) × thickness for ring-type flanges, or π/4 × OD² × thickness for blind flanges), plus any hub volume (for Weld Neck flanges), minus the bolt hole volume (number of holes × π/4 × hole_diameter² × thickness). Multiply the net volume by the material density (e.g., 7,850 kg/m³ for carbon steel) to get the weight. Our calculator does all of this automatically for six flange types and nine materials.

The MS (Mild Steel) flange weight formula is: Weight (kg) = [π/4 × (OD² − ID²) × Thickness − n × π/4 × d_hole² × Thickness + Hub Volume] × 7,850 ÷ 1,000,000,000 (all dimensions in mm). For blind flanges, use OD² instead of (OD² − ID²). For WNRF flanges, add hub volume: π/4 × (HubOD² − ID²) × HubLength. The density of mild steel is 7,850 kg/m³ (7.85 g/cm³). In practice, simply select 'Carbon Steel' in our calculator and enter your flange dimensions to get accurate weight in kg.

To calculate flange weight in kg manually: (1) Convert all dimensions to metres or use mm³ and divide appropriately. (2) Calculate body volume: π/4 × (OD² − ID²) × thickness. (3) Subtract bolt hole volume: number_of_holes × π/4 × hole_dia² × thickness. (4) For WNRF, add hub volume: π/4 × (HubOD² − ID²) × hub_length. (5) Multiply net volume (m³) by material density (kg/m³). Example for 4" Class 150 WNRF in MS: net volume ≈ 0.001192 m³ × 7,850 = 9.36 kg. Our calculator handles all unit conversions and automatically subtracts bolt hole volume.

WNRF (Weld Neck Raised Face) flange weight varies significantly by size, pressure class, and material. A typical 4" Class 150 WNRF in carbon steel weighs approximately 9.4 kg. The same size in Class 300 weighs around 15.6 kg, and Class 600 weighs about 21.8 kg. Stainless steel versions are slightly heavier due to higher density (8,000 vs 7,850 kg/m³). Use our calculator with the ANSI B16.5 presets to get exact weights for your specific flange specifications across NPS ½" to 24".

A blind flange (BLRF) is calculated as a solid disc — there is no bore/ID hole. The formula simplifies to: Volume = π/4 × OD² × thickness (minus bolt holes). Then Weight = Volume × Density. Blind flanges are significantly heavier than similar-sized ring flanges because they have no center opening. For example, a 4" Class 150 blind flange weighs approximately 7.3 kg in carbon steel versus 9.4 kg for the equivalent WNRF flange (which is heavier due to its hub).

Stainless steel grades 304 and 316 have a density of 8,000 kg/m³ (0.289 lb/in³), which is approximately 2% higher than carbon steel at 7,850 kg/m³. Duplex stainless steel (UNS S32205) has a density of 7,800 kg/m³. When calculating flange weights, using the correct density matters — a large 24" stainless steel flange can weigh several kilograms more than its carbon steel equivalent due to this density difference alone. Our calculator has all nine material densities built in.

WNRF (Weld Neck) flanges are significantly heavier than SORF (Slip-On) flanges of the same size and pressure class — for example, a 4-inch Class 150 WNRF is about 63% heavier than the equivalent SORF. This is because WNRF flanges have an integrated hub section that adds material mass. SORF flanges have a simpler ring geometry with just a small shoulder for the pipe, making them lighter and more economical. Both types share the same bolt pattern and outside diameter for a given NPS and class per ASME B16.5.

Yes, this calculator fully supports stainless steel (SS) flange weight calculation. Select 'Stainless Steel 304' or 'Stainless Steel 316' from the material dropdown and the calculator automatically applies the correct density of 8,000 kg/m³. All six flange types (WNRF, SORF, BLRF, Threaded, Socket Weld, Lap Joint) support stainless steel. You can also switch to imperial units (lb/in) if needed. Duplex, Hastelloy, Inconel, Monel, and Titanium are also available.

The number of bolt holes depends on the flange size and pressure class per ASME B16.5: For NPS ½" to 3½", typically 4 bolts (Class 150/300). For NPS 4" to 8", typically 8 bolts. For NPS 10" to 14", 12 bolts. For NPS 16" to 24", 16 to 20 bolts depending on class. Higher pressure classes (600+) often have more bolts. Our ANSI B16.5 presets automatically fill the correct bolt hole count for any size-class combination.

ANSI/ASME B16.5 flange weights follow the same volumetric formula as any flange — net volume × material density. The standard specifies the exact dimensions (OD, thickness, bolt circle, bolt sizes) for each NPS and pressure class combination. The weight formula itself is universal: Body Volume + Hub Volume (WNRF) − Bolt Hole Volume = Net Volume, then × Density = Weight. Our calculator includes ANSI B16.5 presets for WNRF flanges (Class 150, 300, and 600) covering ½" to 24" NPS, so you don't need to look up standard dimensions manually.

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Last updated May 17, 2026