Type a line (torque wrench 400 mm crowfoot 60 mm required 200 N·m) or fill in the fields: the line and the fields stay in step.
Enter the wrench length, the length of the crowfoot, the adapter or the extension and the torque required at the bolt, and the calculator gives the setting for a click torque wrench: the extension lengthens the arm, so the same setting puts more torque on the bolt. An adapter at an angle counts with the part of its length that runs along the wrench. It also works the other way, from a setting to the torque at the bolt. It shows the working with your numbers, draws the wrench, the extension and the bolt, and gives a line you can copy or add to a request.
The calculator gives no torque values for bolts and no tightening procedure: the required torque comes from the maker’s documentation for the joint. It takes the hand pulling at right angles to the handle at the point the wrench length is measured to, and a rigid extension lying in the plane the wrench turns in.
The wrench measures the torque about its square drive: the pull F times L. The bolt gets F times the arm from the hand to the bolt, L + E in line. So the setting is T x L / (L + E): 200 N·m at the bolt with a 400 mm wrench and a 60 mm crowfoot needs 200 x 400 / 460 = 173.9 N·m on the wrench.
With the hand pulling at right angles to the handle, only the part of the extension along the wrench axis adds to the arm: Le = L + E x cos a. At 45°, an 80 mm adapter on a 600 mm wrench adds 56.6 mm: Le = 656.6 mm, and 400 N·m needs a setting of 365.5 N·m. At 90° Le = L and the setting is the required torque.
The reverse gives what the bolt gets for a setting: T bolt = T set x Le / L. A 400 mm wrench set to 170 N·m with a 60 mm extension in line puts 170 x 460 / 400 = 195.5 N·m on the bolt, about 15 % more than the setting.
| Case | Relation | Note |
|---|---|---|
| Arm to the bolt | Le = L + E x cos a | L from the grip centre or the marked load point to the square drive; E from the square drive to the bolt centre |
| In line (a = 0°) | Le = L + E | the extension adds its whole length |
| At a right angle (a = 90°) | Le = L | cos 90° = 0: no correction |
| Pointing back (a = 180°) | Le = L - E | the setting is above the torque at the bolt |
| Wrench setting | T set = T x L / Le | below the required torque while Le is above L |
| Torque at the bolt | T bolt = T set x Le / L | the reverse |
| Units | 1 lbf·ft = 1.355818 N·m; 1 lbf·in = 0.112985 N·m | 1 kgf·m = 9.80665 N·m; 1 in = 25.4 mm |
L and E in the same unit; the torque comes out in the unit it went in. The relations take the hand at the point L is measured to, pulling at right angles to the handle.
The in-line relation, setting = T x L / (L + E), with L from the hand to the square drive and E from the square drive to the bolt, is given in an engineering reference on torque wrench adapters, derived from the pull of the hand being the same for both arms, in torque tool makers’ guidance and in independent torque wrench calculators with worked examples (an 18 in wrench with a 3 in adapter: 80 lbf·ft needs 68.57 lbf·ft; a 450 mm wrench with a 60 mm crowfoot: 100 N·m needs 88.2 N·m), which the calculator reproduces. The angle form, Le = L + E x cos a, for a pull at right angles to the handle, with no correction at 90° and a higher setting past 90°, is given in a reference page on bolts and tools, a torque wrench maker’s calculator and an independent calculator; the reverse, setting x Le / L, and measuring L to the centre of the grip or to the load point marked on the handle are given in more than one of them. The conversion factors are the exact definitions of the inch, the pound and standard gravity.
The extension moves the bolt away from the square drive, so the same pull on the handle puts more torque on the bolt. With L the wrench length from the grip centre, or the marked load point, to the square drive and E the extension from the square drive to the bolt centre, in line: setting = T x L / (L + E). A 400 mm wrench with a 60 mm crowfoot and 200 N·m at the bolt: 200 x 400 / 460 = 173.9 N·m. An 18 in wrench with a 3 in extension and 80 lbf·ft at the bolt: 80 x 18 / 21 = 68.57 lbf·ft.
Only the part of the extension along the wrench axis lengthens the arm, as the hand pulls at right angles to the handle: Le = L + E x cos a, and the setting is T x L / Le. At 45° an 80 mm adapter on a 600 mm wrench adds 80 x 0.7071 = 56.6 mm, so 400 N·m at the bolt needs a setting of 400 x 600 / 656.6 = 365.5 N·m. At 90° cos a is 0 and the setting is the required torque; past 90° the extension points back toward the handle, Le is shorter than L and the setting is above the required torque.
The other way round: the torque at the bolt = setting x Le / L. A 400 mm wrench set to 170 N·m with a 60 mm extension in line puts 170 x 460 / 400 = 195.5 N·m on the bolt. This shows what a bolt got when it was tightened through an extension and the setting was not corrected.
L from the centre of the hand grip to the centre of the square drive; where the handle has a marked load point, measure to it and pull there. E from the centre of the square drive to the centre of the bolt. The overall length of the wrench body is not L.
The calculator does not say: it gives no torque values for bolts and no tightening procedure. The required torque comes from the maker’s documentation for the joint; the calculator turns that figure into the wrench setting for the extension used.
The wrench length and the extension length in mm, cm, m or inches; the torque in N·m, lbf·ft, lbf·in or kgf·m, required at the bolt or set on the wrench, with the result in the same unit and in the others; the angle from 0 to 180°, in line when it is not given. The wrench up to 5 m, the extension up to 3 m. 1 in = 25.4 mm, 1 lbf·ft = 1.355818 N·m, 1 lbf·in = 0.112985 N·m, 1 kgf·m = 9.80665 N·m.
The calculator gives the wrench setting for the extension used. When bolts, studs, nuts or parts of the joint are needed, send the line from the calculator with the equipment details and a photograph of the nameplate, and Vessel Core checks the details before an offer goes back.
