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Construction glossary · Process and contract terms

What is CSI MasterFormatin construction?

CSI MasterFormat is the standard classification system, published by the Construction Specifications Institute, that organizes US and Canadian construction specifications and cost information into 50 numbered divisions. Each division covers a work result, such as Division 03 Concrete or Division 09 Finishes, and breaks into six-digit section numbers like 03 30 00 Cast-in-Place Concrete. Estimators use those same numbers to organize takeoffs, cost codes, and subcontractor bid packages so every line in an estimate ties back to a spec section.

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Updated August 2026 · Reviewed by the Ruh construction team

Divisions 00 to 49 (50 total)Div 03 = ConcreteDiv 26 = Electrical

How MasterFormat organizes a spec

Div 00-01 contractingDiv 03 concreteDiv 09 finishesDiv 23 HVAC / Div 26 electricalStandard 50-division spec numbering system
The definition

CSI MasterFormat, explained.

MasterFormat is the Construction Specifications Institute's system for organizing construction information by work result, meaning the materials and methods that end up in the building. On a US commercial job it shows up everywhere an estimator works: the project manual, where every spec section carries a MasterFormat number (09 29 00 Gypsum Board); the drawings, where keynotes and finish schedules reference those sections; and the contract documents, where bid forms and the schedule of values break out by division. Architects and spec writers structure the project manual with it, general contractor estimators use it to organize estimates and scope bid packages, and subcontractors identify their work by section number. New estimators trip on a few things. They treat one division as one subcontractor, when Division 09 Finishes alone can be five separate subs (drywall, tile, resilient flooring, paint, acoustical ceilings). They skip Divisions 00 and 01, where bonds, allowances, and general requirements carry real money. And they confuse the old 16-division format with the current 50-division structure, which moved mechanical and electrical work into Divisions 21 through 28.

How it is measured

MasterFormat is a numbering scheme rather than a quantity, so you apply it instead of measuring it. Section numbers run in two-digit pairs: the first pair is the division, and the following pairs narrow the work, so 09 29 00 reads as Division 09 Finishes, gypsum board. The numbers appear in the spec table of contents, on every spec section header, in drawing keynotes, and on bid forms. In the estimate, each takeoff quantity keeps its own unit and gets coded to a section: cast-in-place concrete in cubic yards under 03 30 00, structural steel in tons under 05 12 00, gypsum board in square feet under 09 29 00. The discipline is one quantity, one unit, one code, so the estimate rolls up cleanly by division for bid day.

Worked example

A worked CSI MasterFormat example.

Worked example

Take a small warehouse office build-out and map the takeoff to cost codes. Division 03: the slab on grade measures 4,500 sq ft at 6 in. thick, so 4,500 sq ft x 0.5 ft = 2,250 cu ft, and 2,250 cu ft / 27 = 83.3 cu yd, carried as 85 cu yd with waste under code 03 30 00. At an illustrative $250 per cu yd placed and finished, 85 cu yd x $250 = $21,250. Division 05: the mezzanine framing takes off at 12 tons of structural steel under code 05 12 00. At an illustrative $4,200 per ton furnished and erected, 12 tons x $4,200 = $50,400. Division 09: partitions take off at 9,600 sq ft of gypsum board under code 09 29 00. At an illustrative $3.10 per sq ft hung and finished, 9,600 sq ft x $3.10 = $29,760. The roll-up reads $21,250 + $50,400 + $29,760 = $101,410, with every line tied to a spec section and a cost code.

How Ruh handles it

How Ruh handles CSI MasterFormat.

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CSI MasterFormat: frequently asked questions

What is the difference between CSI MasterFormat and UniFormat?+

MasterFormat organizes information by work result, meaning the materials and methods that go into the building, which is why spec books and detailed estimates follow it. UniFormat organizes by building system or assembly (substructure, shell, interiors), which fits conceptual estimates when drawings are thin. A common workflow is to budget schematic phases in UniFormat, then shift to MasterFormat cost codes once the documents support a real takeoff.

What happened to Division 15 and Division 16?+

The 2004 edition retired both. Division 15 Mechanical split into Division 21 Fire Suppression, Division 22 Plumbing, and Division 23 Heating, Ventilating, and Air Conditioning, while Division 16 Electrical split into Division 26 Electrical, Division 27 Communications, and Division 28 Electronic Safety and Security. Plenty of subcontractors and older cost data still say Div 15 and Div 16, so a working estimator needs to translate between the old and current numbering.

Do estimators have to use MasterFormat for cost codes?+

No standard forces it, but most US commercial general contractors base their cost codes on MasterFormat because specs, bid forms, and published cost data already follow that numbering. Matching your codes to the spec sections makes scoping bid packages and tying buyout back to the estimate much faster. Companies with legacy code systems usually keep a mapping table between their internal codes and MasterFormat numbers.

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Related terms

BuyoutAIA G702SubcontractorMEP tradesPurchase order (PO)General contractor (GC)RFQ (request for quotation)

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