Spruce pine strength rating
If your spruce is seasoned spruce from Sweden (aka 'white Baltic') it can be visually stress-graded to Australian Standard 2858, Timber - Softwood - Visually stress-graded for structural purposes. Achievable grades for seasoned spruce (moisture content 15% or less) are F5, F7, F8 and F11, depending on quality, particularly with respect to knot sizes and slope of grain. AS 2858 gives limiting knot sizes for each grade and maximum allowable slope of grain.