F-grade timber

F-grade timber is the stress-grading system for structural timber under AS 1720 (the timber structures standard), used to classify hardwood and visually-graded softwood for AS 1684 span tables. The “F” number expresses the characteristic bending strength in megapascals: an F8 piece has a bending strength of roughly 8 MPa, an F17 piece around 17 MPa.

The common F-grades in Australian residential framing are F5, F7, F8, F11, F14, F17, F22, F27 (in ascending strength). F5 and F7 cover lower-load applications such as wall studs; F8 and F11 are typical for floor and ceiling joists; F17, F22, and F27 are used for hardwood bearers, beams, and high-load members. F34 covers heavy structural hardwood outside the residential range.

F-grade and MGP are parallel grading systems. F-grade is determined by visual grading (knot size, slope of grain, splits) or by mechanical grading, and it applies to unseasoned hardwood and softwood. MGP is determined by machine stiffness measurement and applies only to seasoned softwood (pine). Both systems feed AS 1684 span tables; the tables are keyed to grade, not species, so the chippy reads the span table for the relevant grade and uses any timber meeting that grade.

The grade stamp on the timber or the supplier’s delivery docket confirms the grade. Without a verified grade, a piece cannot be safely entered into an AS 1684 span table.

Also known as: F-grade, F-stress grade, hardwood stress grade.

Category: Structural timber / grading system.

Related

• Hardwood structural timber
• Pine framing grades
• AS 1684 timber framing standard

See also

• Stress grade
• MGP10 (machine-graded pine)
• Span tables
• LVL beams

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Last updated: 2026-05-14. Verified: 2026-05-14.