If you came here for a bolt torque chart to tighten structural steel connections, the honest answer is that no such chart is valid. For high-strength structural bolts, torque is not the specification. The specification is bolt tension, measured in kips, and the accepted ways of reaching it do not involve looking up a torque value in a table. Torque charts do exist and are useful, but for a different family of fasteners and a different purpose. This page explains which is which, and gives the numbers that actually govern.
Why Structural Bolts Are Not Torqued to a Number
Torque is an indirect measurement. When you turn a nut, most of the effort goes into overcoming friction in the threads and under the nut face, not into stretching the bolt. The share lost to friction changes with lubrication, thread condition, whether the bolt is galvanized, how the zinc was applied, how long the assembly has sat in the weather, and which production lot the bolts came from. Two bolts of the same diameter and grade can need noticeably different torque to reach the same tension.
That is why a generic torque-tension table cannot be trusted on a structure. The relationship it assumes is only true for the specific lot, diameter, length, and surface condition it was derived from. Use a table from a catalog on a different lot of bolts and the resulting tension can be well under, or well over, what the connection was designed for. Under-tensioned slip-critical joints slip. Over-tensioned bolts have already been stretched close to their limit and have little reserve left.
The Four Accepted Pretensioning Methods
Caltrans, following the Research Council on Structural Connections (RCSC) Specification, recognizes two standard methods and two alternative methods for tensioning high-strength bolts:
| Method | Type | How tension is controlled |
|---|---|---|
| Turn-of-nut | Standard | Nut is rotated a prescribed fraction of a turn past snug tight |
| Calibrated wrench | Standard | Wrench set from a daily calibration on the actual bolts being used |
| Twist-off tension control bolts | Alternative | A splined end shears off when tension is reached |
| Direct tension indicator (DTI) | Alternative | A washer with protrusions that flatten a measurable amount |
Every one of these requires that the fasteners first pass pre-installation, calibration, and rotational capacity testing at the job site before they go into the structure. All four also require that every bolt in a joint be brought to a snug-tight condition first, with the plies in firm contact, before final tightening begins. Snugging and final tightening both follow a systematic crisscross pattern so the joint tensions evenly rather than being pulled tight at one end.
The Numbers That Do Govern: Minimum Bolt Pretension
This is the table that replaces a torque chart. These are the minimum pretension values for pretensioned and slip-critical joints. They come from a simple rule: 70 percent of the specified minimum tensile strength of the bolt, applied over its tensile stress area.
| Diameter (in) | Tensile stress area (in²) | Grade A325 (kips) | Grade A490 (kips) |
|---|---|---|---|
| 1/2 | 0.142 | 12 | 15 |
| 5/8 | 0.226 | 19 | 24 |
| 3/4 | 0.334 | 28 | 35 |
| 7/8 | 0.462 | 39 | 49 |
| 1 | 0.606 | 51 | 64 |
| 1-1/8 | 0.763 | 56 | 80 |
| 1-1/4 | 0.969 | 71 | 102 |
| 1-3/8 | 1.155 | 85 | 121 |
| 1-1/2 | 1.405 | 103 | 148 |
You can check any row. Grade A325 has a specified minimum tensile strength of 120 ksi up to 1 in diameter and 105 ksi above that. Grade A490 is 150 ksi throughout. For a 3/4 in A325 bolt: 0.70 × 120 ksi × 0.334 in² = 28.1 kips, which rounds to the 28 in the table. For a 1-1/4 in A325: 0.70 × 105 × 0.969 = 71.2, giving 71. The jump in the A325 column between 1 in and 1-1/8 in is not an error; it is the drop in specified tensile strength from 120 to 105 ksi.
Both grades are now covered by the consolidated ASTM F3125 standard, where they appear as Grade A325 and Grade A490 rather than as separate specifications. Drawings and mill certs may still use either style of reference. See bolt grades explained for how these compare with the SAE grades used on machine bolts.
Turn-of-Nut: The Rotations
Turn-of-nut works because bolt stretch is a geometric consequence of nut rotation, and geometry does not care about friction. Past snug tight, the nut is turned 1/3, 1/2, or 2/3 of a turn, with the exact fraction depending on the bolt length relative to its diameter and on the slope of the outer faces. The governing values and their tolerances are in RCSC Table 8.1.
Match-marking is a mandatory part of the operation, not an optional check. After snugging, four marks are made at the turned end of each fastener: a mark on one corner of the nut, a start line on the outer ply aligned with it, a radial line across the end of the bolt tail, and a finish line on the outer ply at the required fraction of a turn past the start.
The radial mark on the bolt tail is the clever part. If, after tightening, that mark no longer lines up with the start line, the bolt itself rotated instead of only the nut. The bolt was not properly backed up, the rotation went into spinning the bolt rather than stretching it, and the tension may be below the required minimum. An inspector can see that from across the joint without any instrument.
Where Torque Genuinely Belongs
Torque has two legitimate roles on a structural job, and neither is “look up a number.”
1. As a calibrated setting, recalibrated daily
The calibrated wrench method may be used only when the equipment and procedures are calibrated daily for each diameter, length, grade, and production lot of bolts being installed. Wrenches must also be recalibrated whenever a noticeable difference appears in the surface condition of the bolt threads, nut threads, or washers. The wrench is then set to deliver a tension not less than five percent in excess of the minimum, so normal scatter still lands above the requirement. Hardened washers go under the turned element.
So the torque value in this method is real, but it is generated that morning, for those bolts, and it expires. It is not transferable to another job, another lot, or the next day.
2. As an arbitration torque for inspection
After a joint is fully tensioned it gets inspected: a visual check that the plies are in full contact and that thread stick-out is within range and uniform, then a “job inspecting torque” applied to 10 percent of the fasteners in each joint. Section 10 of the RCSC Specification calls this the arbitration torque. It is a pass/fail audit of work already done, used to settle disputes about whether a joint was properly tensioned. It is not the installation spec.
The Ten-Second Rule
One field heuristic is worth knowing because it catches a common and invisible error. With a correctly sized pneumatic impact wrench, reaching the required minimum tension after snugging should take roughly 10 seconds. If a bolt comes up tight in four seconds or less, the wrench is too powerful for that bolt size and grade.
That matters because an over-powerful wrench can neck down the threaded shank and stretch it plastically close to ultimate capacity. The bolt looks installed and may even pass an arbitration check, but most of its ability to stretch and deform without breaking has been used up. The opposite failure is just as real: an undersized, worn, or damaged impact wrench will not reach minimum tension in the ten-second window, and hammering away at the nut to force it does not fix that.
What to Put on the Drawing
Specify the joint type, not a torque. A connection is detailed as snug-tight, pretensioned, or slip-critical, and that choice drives everything downstream. Snug-tight is adequate for most bearing connections in statically loaded structures. Pretensioned and slip-critical joints are where the table above applies, and where installation method, testing, and inspection all have to be called out. Faying surface condition matters for slip-critical joints, so note whether coatings are permitted and which class applies.
Related reading: anchor bolts for column-to-concrete connections, gusset plates and moment connections for where these bolt groups actually live, and weld symbols for the welded alternative.
Bolt Torque FAQ
Is there a torque value for a 3/4 inch A325 bolt?
Not one you can look up and rely on. The requirement is 28 kips of tension. The torque needed to produce 28 kips depends on that lot of bolts and their surface condition, which is exactly why the calibrated wrench method requires a daily calibration rather than a published figure.
Why do catalogs publish torque-tension tables then?
Those tables are generally for SAE-grade machine bolts and general mechanical assembly, where the consequence of scatter is different and no slip-critical requirement exists. They are not written for structural steel joints, and standard torque-tension relationships are not an accepted pretensioning method for them.
What is snug tight?
The condition where all plies of the joint are in firm contact. It is the starting point for every pretensioning method, and for many ordinary bearing connections it is also the finished condition.
Can I reuse a high-strength bolt?
Treat this as a question for the engineer of record and the governing specification, not a field decision. Pretensioning takes the bolt into a controlled amount of permanent stretch, so a bolt that has been fully tensioned once is not in its original condition. Galvanized bolts in particular are not reused.
Sources: Caltrans Bridge Construction Records & Procedures Manual, BCM 55-1.03 Attachment 3, “Approved Methods of Tensioning High-Strength Bolted Connections” (04/25/23), for the accepted methods, the daily calibration and five percent requirements, the ten-second guidance and the arbitration torque. Pretension values are 0.70 × specified minimum tensile strength × tensile stress area, consistent with RCSC Table 5.2; nut rotations are per RCSC Table 8.1. Last updated: September 2026.
This page is reference information only and is not engineering advice. Bolted connections are life-safety elements. Do not use this page to install or accept a connection without the project specification and a licensed engineer. Full disclaimer.