How to Measure Knife Blade Length (OTF and Folding) to Stay Legal in 2025

If you carry an automatic, the first rule is knowing how to measure knife blade length the right way. Why? Because blade-length limits show up in state statutes, city ordinances, and even brand policies for workplaces and venues. A clear, consistent measurement keeps you on the right side of the rulebook and helps you choose the right OTF for where you live, work, and travel.

Here’s the no‑drama way to do it, grounded in the industry standard and tested on real OTFs.

Why blade length measurement matters

• Laws often hinge on a hard number. California’s “switchblade” definition keys off a 2.0 inch threshold, which is why micro and nano OTFs exist in the first place. If you measure wrong, you can choose the wrong knife. See the statute language here for context: California Penal Code §17235.
• Retail filters and product pages use blade length to help you sort options quickly. If you know your limit, you can jump straight to compliant models in our CA‑Legal OTFs collection and our tiny powerhouses in Nano OTFs.
• Competence and safety. A clear measurement process reduces guesswork when you’re picking a tool for work, rescue, or EDC.

The industry standard: AKTI’s measurement protocol

When in doubt, lean on a standard. The American Knife & Tool Institute (AKTI) publishes a simple, transparent protocol for measuring blade length across knife styles. The big idea is this: measure the shortest straight line from the blade tip to the forward‑most point of the handle or hilt, then round down to the nearest 1/8 inch. That’s it. You can read the full protocol in AKTI’s guide: AKTI Protocol for Measuring Knife Blade Length.

Why the “shortest straight line”? Because blade and handle shapes vary wildly—tanto vs. drop point, choils, guards, angled handles, flared bolsters. Using a consistent straight‑line method avoids inflated numbers caused by curves and angles.

Why round down to the nearest 1/8 inch? Because real‑world measuring isn’t laboratory precise. Common rulers are coarse, tips chip, handles vary. Rounding down introduces a safety margin in your favor and lines up with the protocol’s practical intent.

Step‑by‑step: measure your OTF, folder, or fixed blade

You’ll need: a flat surface, good light, and a straight‑edge ruler or calipers with inch increments (1/8 inch markings are fine).

1. Close the knife (for folders and OTFs). Place it on a flat surface with the blade tip aligned visually.
2. Identify the two points you’ll measure between:
   • Blade tip: the very apex of the cutting end.
   • Forward‑most handle point: the closest part of the handle or hilt to the tip when closed (folders/OTFs) or when the knife is at rest (fixed blades). On many OTFs, this is the interior lip of the handle opening.
3. Measure the shortest straight line between those two points. Do not trace curves. Do not measure along the edge. Drop your ruler’s zero at the forward‑most handle point and read where the blade tip lands.
4. Round down to the nearest 1/8 inch. If your readout is 2.01 inches, call it 2.0 inches. If it’s 2.12 inches, call it 2.0. If it’s 2.24, call it 2.125.
5. Record it. If you’re traveling or crossing jurisdictions, snap a quick photo of the measurement in case questions arise later.

Edge cases that confuse people (and how to handle them)

• Deep choils or ricassos: The forward‑most handle point is still the nearest handle or guard surface to the tip, not the start of the sharpened edge. Don’t measure only the sharpened portion; measure the blade, not the bevel.
• Recurves and bellies: Curves don’t matter—straight line only. Lay the ruler to connect the tip to the handle’s closest point.
• False edges and swedges: A swedge without an actual cutting edge is not an “effective cutting edge.” It doesn’t change blade length for measurement. AKTI’s definitions page clarifies terms like “double‑edged” and “effective cutting edge.” It’s worth a skim: AKTI Approved Knife Definitions.
• Double‑edged daggers: Measurement is the same; the legal status may not be. Some states restrict double edges regardless of length. Know both the length rule and the edge rule before you carry.
• Flared guards and angled handles: Find the forward‑most point of the guard/handle and measure to the tip. If the handle is angled, the forward‑most point may be higher or lower than you think—use your eyes and keep the line straight.

OTF‑specific nuances

• What part of the handle counts? On most OTFs, the forward‑most point is the inside face of the handle opening (where the blade emerges). That’s closer to the tip than the front face of the chassis; measure from that inside lip to the blade tip.
• Single‑ vs. double‑action: The measuring method is identical. Whether you retract manually (SA) or via the same switch (DA), you’re still measuring tip to forward‑most handle point.
• Full‑size vs. nano: “Nano” and “micro” are marketing labels. Always verify the actual length. Our Hornet Nano OTF and Wasp Nano OTF are designed for jurisdictions with tight limits—verify your number using the protocol above.

Laws evolve—measure right and re‑check the rules

Today’s legal landscape is far friendlier to responsible knife owners than it was a decade ago, and changes continue. For example, as of July 31, 2025, Delaware legalized automatic knives—proof that statutes can move toward common sense. See AKTI’s update here: Delaware Legislature Passes Automatic Repeal.

California is a classic example where measurement rules matter. The state defines “switchblade knife” by mechanism and a 2‑inch blade threshold. That means sub‑2‑inch automatics are outside that definition; 2 inches or more are in. Read the wording yourself here: California Penal Code §17235. If you’re shopping for a compliant automatic, start with our curated CA‑Legal OTFs and, when you want more reach where permitted, step up to the all‑purpose SideKick OTF or our broader OTF collection.

Important: Laws can vary wildly by city or county even within the same state, and some places regulate double edges, serrations, or carry type (open vs. concealed) regardless of length. For a deeper legal overview beyond length alone, see our explainer: Are OTF Knives Legal? State Laws on OTF Knives.

Travel snapshot: TSA rules for flights

TSA keeps it simple: knives don’t go in carry‑on bags, period. Put them in checked luggage, sheathed or wrapped, so they don’t injure baggage handlers or inspectors. Confirm the policy here: TSA — Knives. That rule applies regardless of blade length or mechanism.

Buying smart with a measurement mindset

• Start with your limit. If your city or workplace has a 2.5‑inch limit, filter by that first to avoid second‑guessing later.
• Pick the job, then the geometry. Once you’re inside the limit, choose the blade profile and edge that matches your tasks. Need a balanced EDC? Consider the SideKick OTF. Need compact and compliant for strict zones? Check Nano OTFs. Want maximum versatility where legal? Browse all Out‑The‑Front knives.
• Document once. Measure and jot the number in your notes app or on the box. It saves time the next time someone asks, “How long is that blade?”

Quick checklist (save this)

• Measure the shortest straight line from tip to forward‑most handle point.
• Round down to the nearest 1/8 inch.
• Don’t measure along the edge or only the sharpened portion.
• Double‑edged status is a separate legal question; check both length and edge rules.
• Flying? Knives go in checked bags—never carry‑on.

FAQ

Does the measurement change if my OTF has a false edge on top?

No. A swedge or false edge doesn’t affect blade length. Measure tip to the closest handle point, straight line, and round down to the nearest 1/8 inch.

My micro OTF reads 2.02 inches on calipers. Am I safe under a 2.0 inch rule?

Round down per the protocol. 2.02 inches becomes 2.0 inches. But remember: enforcement discretion exists. If you’re on the bubble, consider a true sub‑2.0‑inch model from our CA‑Legal OTFs or Nano OTFs.

Do TSA rules make exceptions for tiny knives?

No. The carry‑on rule bans knives of any size; pack them in checked luggage and sheath or wrap them. See the policy: TSA — Knives.

Bottom line

Know your number, measure it the right way, and carry confidently. If you’re shopping for a compliant automatic, start with micro and nano options, then size up where allowed. When you’re ready, we’ll help you pick the right OTF for your life—no drama, just gear that works.