Effective January 1, 1987; revised December, 2003; revised July 2026

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For nearly 40 years the REBNY Standard for Commercial Building Measurement, or the 1987 Diary standard as it is fondly known, has guided lease negotiations in an evolving office market and changing commercial tenant needs.

Prior to 1980s,local customs ruled, with no major regional or national standards for building measurement. In the 1980s both REBNY and BOMA (Building Owners and Managers Association, a national trade group), adopted uniform standards. While BOMA continued to update its standards, becoming the national bellwether, the 1987 Diary Standard remained static. In 2003 REBNY provided major updates to its standards codifying method of calculation for rentable area, revised rules on perimeter measurements to conform with national standards, and standardized treatment of common areas. BOMA 2017 and the 2024 update provided for the first significant changes to measurement standards since 1996. Changes in rules allow landlords to include certain outdoor space and amenities in rentable area. No such updates were undertaken to the 1987 Diary Standard.

The Covid pandemic quickly reshaped our city, challenging assumptions on square footage needs, amenities, and what makes a building viable or obsolete for the approximately 550 square feet of office space citywide. Many buildings and owners adapted and innovated. The 1987 Diary Standard did not; it was overdue for a renovation job itself.

To maintain REBNY’s longstanding position as a provider of guidance on the methodology for calculating office building floor measurements, REBNY convened a cross-industry taskforce of owners, brokers, architects and leasing attorneys with one goal: update a nearly 40-year-old document to better reflect current office building design, contemporary amenity practices, and national measurement approaches.

Over the course of the last two years the REBNY Building Measurement Task Force conducted professional studies, met with a wide set of industry experts, and produced recommendations to amend existing guidance to align them more closely with current national practices, and provide greater clarity regarding the treatment of amenity and exterior spaces.

Summary of Updated Guidance

• Defines usable area for traditional office buildings using exterior building measurements while excluding specified building infrastructure and non-tenant-serving areas.

• Permits certain exterior areas—including terraces, balconies, rooftop spaces, plazas, setbacks, and similar areas—to be included in leasing square footage calculations when they are available for tenant use.

• Establishes a formal methodology for defining and allocating Tenant Amenity Space (TAS), including shared conference facilities, health and fitness centers, outdoor amenity areas, and similar tenant-focused amenities.

• Provides a standardized method for allocating corridors, shared areas, and amenity spaces across multiple-tenant floors.

Key Study Areas

EXTERIOR AREAS

Current REBNY measurement standards, last updated in 2003, do not include exterior space. REBNY calls for users to “measure the floor to the outside surface of the building” and simply excludes exterior portion of the building.

Prior to 2017 national standards (BOMA 1996 / 2010) and REBNY standards on exterior space were effectively the same. BOMA measures certain exterior areas but excludes those spaces from rentable area calculation.

In 2017 recognizing “the increasing demand for well-appointed exterior amenities in office buildings,” BOMA updated standards allowing landlords to include finished, usable, tenant-exclusive outdoor spaces in rentable area calculation.

RECOMMENDATION: After studying the details and process surrounding exterior areas in BOMA 2017/24 it is the Taskforce’s recommendation to revise REBNY standards to include certain exterior areas in rentable area calculations while maintaining REBNY methodology of measuring all areas and subtracting non-applicable portion when calculating rentable area.

TENANT AMENTIY SPACE (TAS)

• Current REBNY measurement standards do not account for the concept of “Amenities”.

• Prior to 2017 national standards (BOMA 1996 / 2010) and REBNY standards treatment of building amenities were effectively the same. BOMA measures certain amenity areas but excludes those spaces from rentable area calculation, REBNY fully excluded.

• In 2017 BOMA updated standards allowing for shared amenity spaces to be included in a buildings Load Factor / R/U Ratio. Including amenity areas in rentable area calculation aligns cost with benefit: tenants who enjoy premium enhancements such as gyms, lounges, or private meeting suites bear a proportional share of the cost of providing them.

RECOMMENDATION: After studying the details and process surrounding Building Amenity Areas in BOMA 2017/24 it is the Taskforce’s recommendation to revise REBNY guidance to include qualified amenity spaces in rentable area calculations. In order to achieve this while conforming with REBNY methodology, Tenant Amenity Spaces (TAS) shall be measured and included in add-on factor substantially similar to REBNY’s existing process for measuring multi-tenant floors

See the Case Study

New Guidance:

RENTABLE AREA:

Because of numerous physical dissimilarities among buildings, and Landlords’ varying measurement approaches, calculations of rentable area will often differ from building to building. As a result, in order to facilitate a comprehensive basis for comparing the cost of space across these variations, the Real Estate Board of New York (REBNY) is updating the 1987 Diary Standard to create a modern guidance document that will clearly explain how useable and, ultimately, rentable area may be calculated based upon such usable area. Architectural plans and calculations should be made available to the tenant if requested.

REBNY recommends the following methodologies as guidance for the calculation of Floor Measurements in office buildings. Any Board member who advertises office space for rent may elect to follow these guidelines in determining any rentable area count mentioned in the advertisement.

USABLE AREA, SINGLE TENANT FLOORS (TRADITIONAL OFFICE BUILDING):
Measure the floor to the outside surface of the building; this is defined as the “Interior Area”. To measure any unenclosed exterior portions of the building, measure from the outside surface of the building wall to constructed edge of the unenclosed area provided. If the unenclosed area is not directly adjacent to the enclosing wall (e.g. building rooftop), then measure the entire unenclosed area to the constructed edge. The exterior portions include but are not limited to patios, setbacks, terraces, balconies, rooftops, plazas, driveways, alleys and other outdoor spaces (“Exterior Areas”). Subtract from this area the following, including the nominal four-inch enclosing walls:

• Public elevator shafts and elevator machines and their enclosing walls.

• Public stairs and their enclosing walls.

• Heating, ventilating, and air-conditioning facilities (including pipes, ducts and shafts) and their enclosing walls, unless such equipment, mechanical room space, or shafts serve the floor in question.

• Fire towers and fire tower courts and their enclosing walls.

• Main telephone equipment rooms and main electric switchgear rooms, except that telephone equipment, and electric switchgear rooms serving the floor exclusively shall not be subtracted.

• Any portion of an Exterior Area that is inaccessible to office tenants, is accessible to the general public, is used primarily for base building mechanical equipment, acts as a loading dock / driveway (or similar use), or functions exclusively as a roof assembly, except that any area with mechanical equipment exclusively servicing an individual tenant space shall not be subtracted.

USABLE AREA, SINGLE TENANT FLOORS – BUILDINGS WITH TENANT AMENITY SPACE:
Tenant Amenity Space (TAS) shall be defined as (A) spaces within an office property that are designed, constructed, and maintained to enhance the functionality, well-being, productivity, or overall experience of an office building’s occupants and (B) consists of physical areas that are provided for the discretionary use of tenants, employees, or visitors. TAS designation shall not apply to space(s) where Landlords are separately charging for utilization beyond Landlord’s reasonable out of pocket costs to operate and maintain such space(s). Examples of TAS included but are not limited to, event & and conferencing spaces, health and fitness centers, communal outdoor space & and private plazas, and day care facilities.

• First, calculate the usable area as if for a Traditional Office Building single tenant floor.

• Then, measure the net usable area of any TAS, as defined below, by measuring each enclosing wall which is a building exterior wall to the outside surface of the exterior wall, or to the outside surface of the glass, as the case may be. Measure demising walls to the center and walls which abut corridors to the corridor side of the finished surface of the corridor wall.

• Finally, apportion the TAS to each space afforded access to a TAS by multiplying the net usable area of any TAS by a fraction, whose numerator is the net usable area of the floor being measured and whose denominator is the total of the net usable areas of all the spaces afforded access to the TAS, and add the result to the net usable area of the space being measured.
  

USABLE AREA, MULTIPLE TENANT FLOOR:

• First, calculate the usable area as if for a single tenant floor.

• Then deduct the corridor (do not deduct the enclosing walls of such corridor) and shared areas, including toilets, supply room, heating, ventilating, and air-conditioning facilities (including pipes, ducts and shafts) and their enclosing walls, other shared building systems serving the floor, and any TAS.

• Measure the net usable area of each space on the floor by measuring each enclosing wall which is a building exterior wall to the outside surface of the exterior wall, or to the outside surface of the glass, as the case may be. Measure demising walls to the center and walls which abut corridors to the corridor side of the finished surface of the corridor wall.

• To determine the usable area on a multiple tenant floor, apportion the corridor area and shared areas, including toilets, supply room, heating, ventilating, and air-conditioning facilities (including pipes, ducts and shafts) and their enclosing walls, other shared building systems serving the floor, and any TAS to each space by multiplying the corridor area by a fraction, whose numerator is the net usable area of the space and whose denominator is the total of the net usable areas of all the spaces on the floor, and add the result to the net usable area of the space.

BELOW-GRADE, CELLAR AND SUB-CELLAR SPACE:
To determine the usable area of below grade, cellar and sub-cellar areas, follow the same procedures as are appropriate for single or multiple tenant floors except that the following additional areas should be deducted from usable area:

• Base building machine rooms and pump rooms and their enclosing walls.

• Base building electric switchgear rooms and their enclosing walls.

• Base building telephone equipment rooms and their enclosing walls.

• All space devoted to servicing the operation of the building, i.e., cleaning contractors, storage, building maintenance shop, building engineer's office, etc.
  

RECOMMENDED METHOD OF FLOOR MEASUREMENT FOR STORES:

1. The rentable area of a store shall be computed by measuring from the building line in the case of street frontages, and from the inside surface of the outer building walls to
   the finished surface of the corridor side of the corridor partition and from the center of the partitions that separate the premises from adjoining rentable area.

2. No deductions shall be made for column and projections necessary to the building.

3. Rentable area of a store shall include all area within the outside walls, less the following, with their enclosing walls, if the area is serving more than one tenant: building stairs, fire towers, elevator shafts, flues, vents, stacks, pipe shafts and vertical ducts.

4. The following area shall be included in the rentable area, if such areas exclusively serve a store, together with their enclosing walls: private stairs, private elevators, toilets, air conditioning facilities, janitors' closets, slop sinks, electrical closets and telephone closets. When air conditioning facilities serve more than one tenant area, they shall be apportioned in the same manner used for multi-tenancy floors.

5. Where a store fronts on a plaza or arcade which is intended for use by the general public and is not for the exclusive use of the store tenant, its customers, etc., the area of the plaza or arcade shall not be included in determining the rentable area of the store.