Directions: First, select a version of the IBC (2021 or 2024) and preferred units (Imperial or S.I.). Enter values for occupancy classification, construction type, sprinklers, and proposed number of stories, as well as building perimeter lengths and distance (widths) from building to property lines. Select "yes" if the building is a high-rise (per Section 403 of the 2021/2024 IBC), or if there are 30 or more occupants at a floor level 55 feet or more above the lowest level of fire department vehicular access (per Section 903.2.11.3 of the 2021/2024 IBC) and so on. Press "update" button.
Values are calculated for allowable areas, heights, and numbers of stories for single-occupancy buildings. The site plan (Fig. 1) corresponds to the default values indicated below for a proposed 4-story, fully-sprinklered office building (occupancy of type II-B construction. Distances may be measured from the building to the far side of a "right-of-way" [R.O.W.], as is shown for the building perimeter facing east. In this case, the distance is 35 feet. Some occupancies require sprinklers under certain circumstances: see warnings and error messages.
Building volume, floor area, and distances to property lines may also be constrained by zoning ordinances, which are not considered here.
This calculator only works for single-occupancy buildings, and does not consider all the special conditions listed in Chapter 4 of the 2021 IBC — e.g., things like covered or open malls, and underground buildings. Be sure to check all the special considerations in the code, especially in chapters 4, 5, and 9.
Note that changing the units from "imperial" to "S.I.," or the other way around, will not convert the perimeter lengths and frontage distances entered in the yellow fields; this you have to do yourself!
The "Allowable area per floor" may not be consistent with the site and building geometry used to compute the frontage coefficient. In other words, computing the allowable area per floor doesn't guarantee that the proposed floor/site plan — used in part to calculate that allowable area — is acceptable. This is due, in part, to the way in which the building code is written: it is intended to be used, not primarily as a design tool, but as an analysis tool.
For more information, see my online building code handout.
Fig. 1. Site plan showing yard and building dimensions.
Browser compatibility: Chrome and Safari seem to work best; Firefox works, but its formatting protocols are puzzling and a bit strange — making many of the fields too small and compensating with annoying scroll bars.
Disclaimer: Building codes (including the International Building Code) are typically structured as a maze of basic statements and qualifying assertions. Often, the qualifiers — sometimes found in other sections, or in footnotes to tables — are more important than the basic statements they modify. For this reason, it is important to scrutinize all relevant sections of the code before drawing any conclusions. This calculator does not necessarily account for all qualifying assertions, and so should not be used for the design of actual structures, but only for schematic (preliminary) understanding of building code principles as they apply to allowable heights, stories, and areas. For the design of an actual structure, a competent professional should be consulted.
First uploaded March 10, 2024. Last updated March 18, 2024.
