Free engineering tool
Flange Bolt Torque Calculator
Get a starting bolt torque for a flanged joint. Choose the flange class and size (bolt count and diameter come from the Texas Flange bolt and stud chart) or enter any inch bolt. Then set the bolt grade, target stress and lubricant. The calculator uses the standard short-form torque formula, T = K × D × F, and shows torque per bolt, preload and a three-pass tightening sequence.
Many procedures target 40 to 70% of minimum yield. Limited to 10 to 90%.
4″ Class 150: 8 studs, 5/8-11 UNC
124 ft-lb per bolt
168 N·m per bolt
- Tensile stress area
- 0.2260 in²
- Bolt yield (min.)
- 105,000 psi
- Target bolt stress
- 52,500 psi (50% of yield)
- Preload per bolt
- 11,865 lbf
- Total bolt load (8 studs)
- 94,921 lbf
Tightening passes (star pattern)
- Pass 137ft-lb
- Pass 274ft-lb
- Pass 3124ft-lb
Then a circular check pass at full torque until the nuts stop turning.
Torque-to-preload depends heavily on lubrication, thread condition and washers. Check that the bolt stress suits the gasket (too little leaks, too much can crush it) and follow the gasket maker’s and your site’s bolting procedure.
Reference tool for planning and quoting. Confirm against the purchase specification and your site's procedures before use.
Request a flange quote
Frequently asked questions
How do you calculate bolt torque?
A common short-form formula is T = K × D × F, where K is the nut factor (about 0.20 for dry steel, 0.16 with moly anti-seize), D is the nominal bolt diameter in inches and F is the target preload in pounds. Divide by 12 for ft-lb.
What preload should flange bolts be tightened to?
Many procedures target roughly 40 to 70 percent of the bolt's minimum yield strength. The right value depends on the gasket and the joint, so check the gasket maker's recommendation and your site procedure.
Why does lubricant change the torque?
Most applied torque is lost to friction in the threads and under the nut. A good lubricant lowers friction, so the same preload needs less torque. Using a dry-bolt torque on lubricated bolts can over-stress them.
What is the tightening sequence for a flange?
Tighten in a star (cross) pattern in several passes, for example 30, 60 and 100 percent of final torque, then make a circular check pass at full torque until the nuts stop turning.
What bolts are used on ASME B16.5 flanges?
Alloy steel studs to ASTM A193 B7 with A194 2H heavy hex nuts are the most common choice for carbon steel flanges. Low-temperature service often uses A320 L7, and stainless systems often use B8 or B8M.
