Calculation of Percentages
Some provisions in the ADA Standards specify a minimum number of elements or spaces as a minimum percentage or proportion. Rounding up to the next greater whole number is required where fractions or remainders occur. For example, if the standards require access to at least 5% of an element and a total of 25 are provided, at least 2 must be accessible (rounding up from 1.25).
In the case of specifications for dimensions or sizes that involve percentages or ratios, rounding down for values less than one half is allowed.
Recommendation: Dimensions expressed as a range are intended to accommodate deviations in the field. It is good practice to specify accordingly. For example, for the location of wheelchair accessible water closets (16” – 18” centerline from side walls or partitions), specifying to the midpoint of the range (17”) will accommodate any construction variations up to 1” plus or minus. For dimensions not expressed as an absolute (“X maximum” or “Y minimum”), specify in a manner that accommodates the expected tolerance within the required dimensions by subtracting the tolerance from the required maximum or adding it to the required minimum.
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