This article appeared in Knife Magazine in November 2025
Know Your Knife Laws – How Judges Measure Blade Length
By Anthony Sculimbrene, Attorney and Knife Expert
For all of their utility and antiquity, knives are bafflingly overregulated. We are developing AI that can supplant tens of millions of workers worldwide with almost no regulation, but if you have a pointy piece of steel, be prepared for a myriad of laws telling you what you can and can’t do. I have looked extensively at regulations around deployment methods for folders (i.e., auto knife bans), and I took a peek at legal definitions of concealed carry, but one part of knife laws remains even more legally vexing–measuring blade length. It seems like such a simple thing: how long is this blade? But in reality, it’s not. You can insert your own “lawyers make a mess of everything” joke here.
The reason this is important is that many laws in many states regulate knives based on blade length. The problem is that there is no consistent rule from state to state or between states and the federal government on how to measure blade length. Often, “blade” and “blade length” aren’t defined at all. There are a few different approaches that manufacturers use. Many measure from the furthest forward point on the handle to the furthest forward point on the blade. That seems simple, right? But what if the blade is not sharpened that entire length? For example, Spyderco’s excellent small folder, the Dragonfly II, has a finger choil that is fully unsharpened. Should that portion of the blade be counted? Put another way, do blade length laws measure the length of the blade or the length of the cutting edge?
There are other methods as well. You could measure ALONG the cutting edge. If the blade curves or is serrated, you could have a cutting edge much LONGER than the blade length. This runs into a well-known paradox discovered in 1951 by a mathematician named Lewis Fry Richardson called “the Coastline Paradox,” where the length of an object increases when measured by comparatively smaller units of measure. If you measure the UK’s shore using 100-kilometer units, it is 2,800 kilometers. If you use 50-kilometer units, it is 3,400 kilometers. The same is true of a cutting edge–imagine if you straightened out all of the curves of a serration–the cutting edge would be MUCH longer than the blade length.
So, how do courts measure the length of a blade? This issue has come up many times, but one particular case frames the issue exceptionally well. In re Rosalio S., 35 Cal. App. 4th 775 (1995), the Court had to determine whether a lower court had correctly determined the length of a knife that was used in a crime. If the knife was too long, over 2 ½ inches in this case, the crime was more serious. The knife in question was the blade of a Leatherman. At the trial court level, the judge measured the length of the blade by examining the length of “the metal piece that is exposed from the base of the knife to the tip of the knife.” Id. at 777. When so measured, the blade was 2 ⅝ inches long, an eighth of an inch over the legal limit. Rosalio timely appealed, and on appeal, the main issue was whether this method of measuring blade length was correct. In a stunning surprise, albeit one backed up by good legal reasoning, the appellate court overruled the trial court.
The appellate court started where all good legal analysis starts–with the language of the statute. In this case the statute read as follows: “Any person, except a duly appointed peace officer…who brings or possesses any dirk, dagger, ice pick, [or] knife having a blade longer than two and one half inches [is] in violation of section 626.10…” The problem for the court is that the term “blade” is not defined by statute. When statutes use words that are not defined, courts, under the rules of statutory interpretation, default to their “everyday meaning.” When this happens, courts consult dictionaries, usually Merriam Wester’s Dictionary. They define “blade” as “the cutting part of an instrument.” To drive their point home further, the court consulted yet another dictionary, The American Heritage Dictionary, which defined blade as “the flat-edged cutting part of a sharpened tool or weapon.” Using this approach, the appellate court remeasured the blade and discovered that the cutting edge was 2 ½ inches, the absolute upper limit allowed by statute. They reversed the lower court’s decision and remanded the case.
This decision, of course, is not the last word on the subject. Governments are free to promulgate blade length restrictions AND include a definition of how to measure blade length in those regulations. If the regulations define “blade” or “blade length,” then courts need not consult dictionaries for the “everyday meaning” of a word or term; the regulation definition takes precedence. That said, almost no governmental unit defines blade or blade length in its statute or regulation. This is unlikely to be intentional, just an oversight from legislators that never actually had to consider this issue and how complex it can be (see the Coastline Paradox mentioned above).
The American Knife & Tool Institute (AKTI) has established a recommended protocol for measuring blade length. They recommend that blade length be measured as “the tip of the blade to the forward-most point where the blade transitions to the handle or hilt.” This is perfectly workable as a statutory definition. It also gets at what is really of concern–longer blades allow for greater reach and therefore make it easier to injure someone either by surprise or without the ability to respond. After all, it would be ridiculous to say that a spear has only three inches of reach because the sharpened spear tip is only three inches long.
AKTI’s definition is both better than no definition, and it also gets at what the laws are trying to prevent. Without it, there is a great deal of legal ambiguity in how to measure blade length, though the court in In re Rosalio does the best job of any court that has considered this precise issue, even if their definition is the opposite of AKTI’s. Statutory interpretation is a funny business.