Mechanical Design

Fastener Preload Calculator

Calculate bolt preload and required torque for standard fasteners using the VDI 2230 torque equation — which accounts for both thread friction and bearing face friction.

Inputs

Fastener

13 TPI
Washer or head bearing OD

Grade / material

% of proof load (typically 75–90%)

Results

Preload force (F)

—

lbs

Applied torque (T)

—

in·lb

Nut factor (K)

—

T = K·D·F

Bolt stress (σ)

—

psi

Proof load (F_proof)

—

lbs

Thread torque component

—

in·lb

Preload as % of proof load
— %  
0%Target: 75–90%100% proof

Recommended torque by grade at this fastener size

Grade Proof strength Proof load T @ 75% (in·lb) T @ 85% (in·lb) T @ 90% (in·lb)

VDI 2230 / Shigley Full Torque Equation

T = F · [ p/(2π) + µₜ · rₜ + µᵦ · rᵦ ] rₜ = (D − 0.6495·p) / 2   [mean thread radius, 60° thread] rᵦ = Dₕ / 2   [effective bearing radius ≈ washer/head OD / 2] K = T / (F · D)   [nut factor — validates T = K·D·F] F_proof = Sp · Aₜ   |   σ = F / Aₜ
µₜ = thread friction coefficient µᵦ = bearing face friction coefficient rₜ = mean thread radius (in) rᵦ = effective bearing radius (in) K = nut factor (typically 0.15–0.22) Sp = proof strength Aₜ = tensile stress area