Rebar quantity take-off: outer-surface or centreline length - the 2024 measurement standards expressly adopt the centreline, quota manuals old and new coexist, and how to resolve the difference

Topic Positioning

The long-disputed measurement convention for rebar quantities - whether computed by the outer-surface length or by the centreline length of the bars. This card compares the current conventions of the 2024 measurement standards with several local consumption quota manuals and gives resolution principles for preparing the BOQ, applying quota items and comparing quantities with software.

Core Conclusions

1. BOQ level: the 2024 standards expressly adopt the centreline

• GB/T 50854-2024 "Standard for Method of Measurement of Building and Decoration Works", Table E.6.1 (code 010506 rebar, bolts and ironware): rebar quantities are computed by the centreline length of the bars shown on the design drawings multiplied by the unit theoretical mass; laps and anchorages indicated by the design (including those required by codes) shall be included in the computation.
• GB/T 50860-2024 "Standard for Method of Measurement of Structures", Annex A.15.6: "'length of rebar shown on the design' in the measurement rules means the centreline length of the rebar."

2. Quota level: old and new coexist, each manual must be checked

• New manuals adopting the centreline: Jiangsu 2026 edition - "rebar works shall, distinguishing cast-in-place members, precast members and prestressed members as well as different sizes, be computed per the design drawings, standard atlases and code requirements, by the centreline length of the rebar multiplied by the unit theoretical mass"; the new Shaanxi consumption quota (draft for comment) - "rebar of cast-in-place and precast members is computed by mass, by the centreline length of the rebar shown on the design multiplied by the unit theoretical mass".
• Old convention expressly outer-surface: Hunan 2025 consumption standard for building and decoration works - "when computing the weight of bent-up bars, compute by the outer-surface length, without deducting the elongation".
• Silent conventions: Beijing DB11/T 2382-2024 clause 4.6.9 "rebar, welded mesh and rebar cages of cast-in-place members shall all be computed by mass per the dimensions shown on the design" and clause 7.1.32 (municipal) "quantities of rebar fabrication and erection shall be computed by mass per the dimensions shown on the design" - neither states outer surface or centreline.

3. Resolution principles

• Two separate tracks, no mixing: BOQ quantities follow the measurement standard (centreline); quota quantities follow the rules of the quota manual applicable to the project; quantities computed under one convention must never be applied to quota items of the other.
• Where the quota is silent, lock the agreement first: agree "outer surface or centreline" in the explanatory notes or the contract - the agreed term prevails over general interpretation; the summary-convention setting of the take-off software (by outer surface / by centreline axis) is a tool-level matter that does not change the applicable rule, and switching it changes the quantities at the bent portions (stirrups, tie bars etc.), so the setting should be fixed and recorded in the explanatory notes.
• Check the accompanying conventions in step: construction laps not measured - "apart from laps indicated by the design (including those required by codes), other construction laps (such as stock-length laps) are not measured" (GB/T 50854-2024 Annex E.7.9, item 11); non-design means rebar not measured - "rebar items do not include the quantities of chair bars, diagonal struts, anti-buoyancy bars, spacer plates and other means rebar not required by the design" (item 12).

Applicability Boundaries

• Applicable to the rebar measurement convention of building and decoration works and of structures works; highway, railway and water conservancy works follow the corresponding sector measurement standards / quota manuals.
• Divergent local quota conventions are normal (new editions are transitioning to the centreline while some old or silent conventions remain in force); before preparation, check the text of the quota edition actually applicable to the project - the convention of another province must not be applied across regions.
• The difference between outer-surface and centreline concentrates at the bent portions of the bars; for straight bars and members with few bends the difference is small; when comparing quantities, check the software / convention setting first, then the figures.
• Where the contract expressly agrees a measurement convention, that agreement prevails.

Further Reading

• Measurement standards: GB/T 50854-2024 Table E.6.1 and Annex E.7.9 notes to the rebar items (items 11 and 12); GB/T 50860-2024 Annex A.15.6.
• Quota manuals: Hunan 2025 consumption standard for building and decoration works, rebar quantity computation provisions item 2; Jiangsu 2026 edition "rebar, bolts and ironware" item 1; new Shaanxi consumption quota (draft for comment) rebar item 1; DB11/T 2382-2024 clauses 4.6.9 and 7.1.32 to 7.1.33.