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Bolt torque calculator: tightening torque and preload

Tightening torque and preload of metric bolts M3 to M39, classes 8.8 to 12.9 and A2/A4 stainless, with thread and head friction per VDI 2230. Free.

  • Instant result
  • Formula and standards shown
  • On desktop and phone

Pre-filled example

An M10 bolt, property class 8.8, lightly oiled thread (µG = 0.12), tightened to 90% of its yield strength.

More options (7)
mm
mm
mm
kN
N·m

Result

29.6kNPermissible preload FM

Tighten to 48.5 N·m (M10 8.8, µ 0.12)

Tightening torque MA
48.5N·m
  • Caution : Assembly preload only: service loads, fatigue and surface pressure are not checked.
Attach this calculation to a work order

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Does not replace the manufacturer's value.

Bolt torque written into the work order checklist

Here, the calculator is free and the result is gone when you close the page. In Reglova, it is attached to the work order on the right machine: you find it again at the next breakdown, and on audit day.

The CMMS software comparison, our gaps included
  • Attached to the work order with its inputs: the server recalculates it, it stays verifiable.
  • On the technician's phone, even without a network.
  • In the machine's history, for the next breakdown.
  • The result becomes a checklist step of the work order.
Try the demoJoin the free beta
Reglova · Calculations · Work order WO-AT01-04219
Silent video, 33 s: from the work order for an oil leak on a shear cylinder, the tightening torque of an M12 bolt, then "Attach to the work order". A step to tighten it to 93.1 N·m lands in the checklist (step text from the French demo data). Watch the video

When you need a bolt tightening torque

  1. 01

    Find the torque to set on the wrench when the assembly instructions do not give it.

  2. 02

    See the effect of lubrication: lower friction gives a higher preload at the same torque.

  3. 03

    Write the torque into the work order checklist, so it is the same at every assembly.

Good to know

The calculation covers assembly tightening only: service loads, fatigue and surface pressure under the head are not checked. The machine manufacturer's value always prevails.

VDI 2230 torque and preload formula

For an ISO metric bolt, the calculator gives the permissible preload FM and the tightening torque MA that produces it, from the thread, the property class and the friction coefficients in the thread and under the head. It also works backwards: the torque for a target preload, or the preload obtained with an applied torque.

Formula · Reference documents

FM = ν·Rp0.2·As / √(1 + 3·[1.5·(d2/ds)·(P/(π·d2) + 1.155·µG)]²) ; MA = FM·(0.16·P + 0.58·d2·µG + DKm/2·µK)

VDI 2230-1:2015, R7 ; ISO 898-1, ISO 3506-1, ISO 261, ISO 4017, ISO 273

Inputs and accepted ranges
InputUnitAccepted rangeExample
Thread34 optionsM10
Property class7 options8.8
Thread friction µG0.04 to 0.50.12
Head friction µK0.04 to 0.5Optional
Yield utilization ν0.1 to 10.9
Head bearing diameter dwmm1 to 200Optional
Clearance hole dhmm1 to 200Optional
Mean bearing diameter DKmmm1 to 200Optional
Tightening factor αA1 to 5Optional
Target preloadkN0.01 to 5,000Optional
Applied torqueN·m0.01 to 100,000Optional
Calculated results
  • Permissible preload FMkN
  • Tightening torque MAN·m
  • Minimum preload FM,minkN
  • Torque for the target preloadN·m
  • Resulting preloadkN
What the calculator flags
  • Assembly preload only: service loads, fatigue and surface pressure are not checked.
  • Friction below 0.08 (MoS2, grease): risk of overtightening.
  • Stainless steel: risk of galling, lubricate the thread.
  • The preload exceeds the permissible preload.

The same bolt torque at every assembly, on every shift

  • Breakdowns reported by QR code
  • Work orders on the phone, even without a network
  • Mandatory inspections reminded by email
  • Audit file as a PDF, in one click
Try the demoJoin the free beta

Free during the beta, no credit card