Safety Factor 3.0 to 1 2.5 to 1 2.0 to 1 1.5 to 1 1.0 to 1 1.5 to 1 is recommended as an explicit factor of safety for calculating restrained lengths in most installations. This factor, combined with the conservative values used in these calculations, generate very conservative restrained lengths. Severe conditions and critical installations may require higher factors.