Flange Bolt Torque Calculator
Gives a torque range, not a single number — because the inputs that set flange bolt torque are themselves ranges. Bolt pattern from ASME B16.5, bolt yield from ASTM A193, nut factor from published bands. Every assumption is shown with the answer.
Pick pipe size and flange class. Bolt count and bolt diameter come from ASME B16.5. The torque band is then computed on a fixed, stated basis — A193 B7 studs, lubricated (K = 0.15–0.20), target bolt stress 40–70% of minimum yield. That band is wide on purpose: it is the honest spread before your project spec narrows it. Use Custom mode to pin it down.
Why a range and not a number
Torque wrenches measure torque. Flange joints care about clamp load. The bridge between the two is empirical, and it is loose:
- T — applied torque (in-lb; divide by 12 for ft-lb)
- K — nut factor: thread friction, under-nut friction and geometry rolled into one empirical number
- F — target clamp load (lb) = bolt tensile stress area × target bolt stress
- D — nominal bolt diameter (in)
Two of those four are ranges before you ever pick up a wrench:
- K is not a material property. Published values span roughly 0.10 to 0.30 depending on lubricant, plating and surface condition. Guidance on the PCC-1 simple method makes the consequence explicit — moving K across that span does not shift the required torque by 20%, it shifts it by around 200%.
- Target bolt stress is a design choice, not a constant. For bolted flange joints, a target somewhere in the 40–70% of specified minimum yield band is commonly cited as acceptable, with the actual value set so bolts, flange and gasket all stay within limits. Different gaskets land in very different places inside that band.
That is why two reputable published torque charts hand you different numbers for the identical flange. Both are “right” for their own stated assumptions. Reprinting one of them as though it were a standard is the mistake — so this page computes the band and shows you the assumptions instead.
Even after you fix K and target stress, torque-based tightening still lands within roughly ±25% of target preload lubricated and ±35% dry. If the joint genuinely needs better than that, the answer is bolt-stretch measurement or hydraulic tensioning — not a more precise-looking torque number.
Nut factor bands used by this calculator
| Thread condition | K band | Notes |
|---|---|---|
| Dry / as-received | 0.20 – 0.25 | Widest real-world scatter. Avoid where the torque target assumes lubricant. |
| Oiled or greased | 0.15 – 0.20 | The common default. PCC-1 material references nut factors around 0.15, 0.18 and 0.20. |
| Anti-seize (Ni / Cu based) | 0.12 – 0.16 | Typical for stainless, high temperature and re-bolting. |
| Moly (MoS₂) / PTFE | 0.10 – 0.14 | Lowest practical K. Critical bolting and tensioner-installed studs. |
Bands reflect commonly published nut-factor values — they are not a measurement of your joint. If your project specification names a K, use that one.
The tightening pattern
- Snug — all bolts hand-tight plus a wrench check, flange faces parallel.
- Pass 1: 30% of target, cross (star) pattern.
- Pass 2: 60% of target, same pattern.
- Pass 3: 100% of target, same pattern.
- Pass 4: 100% rotational — clockwise bolt to bolt, at least one full lap with no further movement.
Mark each nut with a paint dot after the rotational pass. If a nut turns on a later lap, go back to Pass 3. The required sequence, pass count and any hold or re-torque interval come from the approved procedure — the above is the common general case.
ASME B16.5 bolt pattern reference
Bolt count and nominal bolt diameter for raised-face flanges, NPS ½” through 24”. This is dimensional data from the standard — unlike torque, it is a fixed published value.
| NPS | 150# | 300# | 600# | 900# | 1500# | 2500# |
|---|
Format: count × nominal diameter. A dash means the size is not covered in that class — NPS 3½” stops at Class 600, and Class 2500 stops at NPS 12”. Class 400 is not shown because it was not independently verified for this rebuild. Bolt circle and flange OD are on the ASME B16.5 flange dimension chart. Always confirm against the current edition of the standard and your project spec.
Frequently asked questions
Sources
Every number this tool uses traces to one of these. Nothing here is a reprinted vendor torque table.
- ASME B16.5 — Pipe Flanges and Flanged Fittings Bolt count and bolt diameter, re-verified September 2026 against independent published charts — Texas Flange, Wermac and Piping World. Classes 600, 900, 1500 and 2500 were confirmed against two or more of those sources, which agree on every entry; Classes 150 and 300 against one. This pass corrected several Class 600–2500 bolt sizes that were previously wrong on this page. Standard at asme.org
- ASME PCC-1-2022 — Bolted Flange Joint Assembly Assembly method, tightening pattern and the target-torque approach. asme.org
- ASTM A193 / A193M Minimum yield strength by grade and diameter for B7, B16, B8M Cl 1 and B8M Cl 2. B7 verified at 105 / 95 / 75 ksi across its three diameter bands. B7 property table
- Nut factor and the PCC-1 simple method Source of the nut factors PCC-1 references (0.15 / 0.18 / 0.20) and of the point that torque is roughly 200% sensitive across the K range. Arveng Training & Engineering
- Target bolt prestress band The commonly cited 40–70% of specified minimum yield range for bolted flange joint assembly. Eng-Tips engineering discussion
- Published example tables — used only as a sanity check Confirmed that the computed band brackets what industry actually publishes. None are reproduced on this page. Class 150 spiral wound (60 ksi, K = 0.18) · Projectmaterials B16.5 chart · Texas Flange reference guide