Bolt Stretch and Clamp Load

Clamp load from F = (stretch * area * E) / grip; cross-check torque.

Run the calculator

Example

You enter

Bolt diameter (in) 0.5
Grip length (in) 3
Target stretch (0.001 in) 5
Fastener material steel
Torque K-factor 0.18

You get

Clamp load 7095 lb
Cross-check torque 53.2 ft-lb
Modulus (psi) 30000000

Details, formula, and sources

Clamp load F = (stretch × area × E) / grip. Stretch is residual elongation after torque; E is fastener elastic modulus per material.

ASTM A325 / A490 / SAE J429 by name; SAE bolt material moduli (steel ~ 30e6 psi, stainless A2/A4 ~ 28e6, Inconel 718 ~ 29.6e6, titanium 6Al-4V ~ 16.5e6, aluminum 2024 ~ 10.6e6).

ASTM / SAE licensed; engineering-property values free in Machinery's Handbook (older editions free at archive.org).

Estimate. AHJ and licensed professional govern.

Field names used by the API: diameter_in, grip_length_in, stretch_thou, material, k_factor, clamp_load_lb, cross_check_torque_ft_lb, modulus_psi

Elastic-region behavior true (stretch < proof-load yield)Hooke's law assumption