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What Is CSI MasterFormat?

By Wyatt Cooper · Published · 3 min read

Key takeaways

  • MasterFormat is the Construction Specifications Institute's standard list of section numbers and titles for organizing specifications by work result.
  • A number like 23 09 00 has three pairs of digits: the division (23, HVAC), then finer levels of the same work.
  • Because the specs use it, contractors reuse it for bid packages, cost codes, submittal logs and the closeout binder, so one number follows the work from bid to turnover.

CSI MasterFormat is the Construction Specifications Institute's standard list of numbers and titles for organizing construction specifications and project information by work result, such as 23 09 00 for HVAC instrumentation and controls. Many contractors reuse the same numbers for bid packages, cost codes, submittal logs and closeout binders, so every document points to the same section.

How MasterFormat numbers work

CSI calls MasterFormat "the construction industry's standardized language for project documentation" that organizes "specifications into work results that contractors can price, procure, and build". It is revised over time: CSI says the 2026 edition "introduces 2,185 new and 617 reorganized listings" (CSI, standards overview).

You can see the numbering in any specification built on it. The federal guide specifications are an example: 01 33 00 is Submittal Procedures and 01 78 23 is Operation and Maintenance Data, both in "DIVISION 01 - GENERAL REQUIREMENTS" (UFGS 01 78 23), and the submittal section cites "Section 23 09 00 INSTRUMENTATION AND CONTROL FOR HVAC" (UFGS 01 33 00). The first pair is the division; the next pairs narrow it.

Example: one number across the job

Where section 23 09 00 shows up on one job (fictional)
DocumentHow it uses 23 09 00
SpecificationSection 23 09 00, the requirements for HVAC controls
Bid packageHVAC controls, scoped to section 23 09 00
BudgetCost code 23 09 00, budget $84,000
Submittal log23 09 00-001 control drawings, 23 09 00-002 product data
Closeout binderTab 23 09 00: O&M manual, warranty, as-built control diagrams

The split into packages is in how to break a job into bid packages, the log in how to set up a submittal log from the specs, and the budget side in what a cost code is.

How it works in Conflo

Conflo uses MasterFormat throughout: budget lines are keyed by MasterFormat cost code and grouped by division with subtotals, the procurement log groups items by CSI division, and the closeout package is grouped by spec section, the way the binder is.

The Budget in Conflo: original, approved changes, revised budget, committed, actual to date and projected final, by CSI division and cost code, with lines not yet bought out flagged and the amount projected over budget.
The budget in Conflo, by CSI division and cost code.

The bottom line

MasterFormat is the numbering that ties the specification to every other document on the job.

Take your section numbers from the project manual and use the same ones for packages, cost codes, submittals and closeout.

See how the budget works in Conflo

Sources

  1. Standards overview: MasterFormat — Construction Specifications Institute (CSI). Read October 22, 2026.
  2. UFGS 01 33 00, Submittal Procedures (August 2026) — Whole Building Design Guide (USACE / NAVFAC / AFCEC). Read October 22, 2026.
  3. UFGS 01 78 23, Operation and Maintenance Data (May 2023) — Whole Building Design Guide (USACE / NAVFAC / AFCEC). Read October 22, 2026.

Questions

Who publishes MasterFormat?

The Construction Specifications Institute (CSI), which revises it over time; the current edition is MasterFormat 2026.

What changed in MasterFormat 2026?

CSI says the 2026 edition introduces 2,185 new and 617 reorganized listings; check the edition your project manual uses before reusing its numbers.

What is Division 01?

Division 01 is General Requirements: the administrative and procedural sections, such as submittal procedures, the project schedule and closeout submittals.

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