From the introduction to Counting Regulations: An Overview of Rulemaking, Types of Federal Regulations, and Pages in the Federal Register (2016):
Certain methods of quantifying regulatory activity, however, may provide an imperfect portrayal of the total federal rulemaking burden. For example, the number of final rules published each year is generally in the range of 2,500-4,500, according to the Office of the Federal Register. Some of those rules have a large effect on the economy, and others have a significant legal and/or policy effect, even if the costs and benefits are minimal. On the other hand, many federal rules are routine in nature and impose minimal regulatory burden, if any. In addition, rules that are deregulatory in nature and those that repeal existing rules are still defined as “rules” under the Administrative Procedure Act (APA, 5 U.S.C. §§551 et seq.) and are therefore included in that total.