How to Measure Chainsaw Chain: Pitch, Gauge, and Drive Links Explained

There is no "universal" chainsaw chain.

Walking into a shop and asking for a "standard 18-inch chain" is like walking into a tire shop and asking for a "standard round tire." It doesn't exist. Chainsaw cutting systems are precision-engineered loops where tolerances are measured in thousandths of an inch.

If you get these measurements wrong, the consequences range from a chain that simply won't mount, to catastrophic damage to your clutch drum and bar rails.

At Alpine Chain Co, we encounter this issue daily. This technical guide will teach you how to correctly measure the "Big Three" specifications: Pitch, Gauge, and Drive Link Count.

The "Bar Length" Trap

Before we touch the calipers, we must dispel the most common myth in the industry: Bar Length is not a technical specification.

The "18-inch" printed on your bar refers to the cutting length (the amount of bar sticking out of the saw), not the physical length of the chain loop.

  • The Reality: One brand's 18-inch saw might run 72 Drive Links. Another brand's 18-inch saw might run 74 Drive Links.

  • The Rule: Never buy a chain based solely on the length of the bar. You must know the specific geometry of the drive system.

1. Pitch: The Geometry of the Drive System

Definition: Chain Pitch is the average distance between the rivets. It effectively determines the "size" of the chain chassis.

Pitch is the most critical variable because it dictates compatibility with your Drive Sprocket (on the engine) and the Nose Sprocket (on the bar tip). These three components must mesh perfectly.

The Formula

You cannot measure pitch by measuring a single link, as link lengths vary. You must measure the distance between three consecutive rivets and divide by two.

$$\text{Pitch} = \frac{\text{Distance between Rivet 1 and Rivet 3}}{2}$$

How to Measure:

  1. Lay the chain flat on a bench.

  2. Using calipers or a ruler, measure from the center of the first rivet to the center of the third rivet.

  3. Divide that number by 2.

The Common Standards:

  • 1/4" Pitch: Used on carving bars and pole pruners. (12.7mm across 3 rivets Ă· 2 = 6.35mm).

  • 3/8" LP (Low Profile): The standard for small Stihl (MS170/180) and domestic saws. (19.05mm across 3 rivets Ă· 2 = 9.525mm).

  • .325" Pitch: The most common mid-range size for 40cc–60cc farm saws. (16.5mm across 3 rivets Ă· 2 = 8.25mm).

  • 3/8" Standard: The professional standard for 70cc+ felling saws. (19.05mm across 3 rivets Ă· 2 = 9.525mm).

  • .404" Pitch: Heavy-duty harvesters and old-school muscle saws. (20.5mm across 3 rivets Ă· 2 = 10.26mm).

Technical Warning:

You will notice that 3/8" LP and 3/8" Standard have the same calculated pitch (0.375"). However, they are NOT compatible. 3/8" LP uses a lower chassis height. Running a Standard chain on an LP sprocket will destroy the drive link tangs.

2. Gauge: The Thickness of the Chassis

Definition: Gauge is the physical thickness of the Drive Link—the shark-fin shaped part of the chain that rides inside the groove of your guide bar.

Gauge is essentially the "fitment tolerance." It ensures the chain stands up straight while cutting.

How to Measure:

You need a set of Vernier Calipers for this.

  1. Clean the oil and sawdust off a drive link.

  2. Clamp the calipers over the thickest part of the drive link (away from the worn bottom edge).

  3. Read the measurement in thousandths of an inch.

The Four Industry Sizes:

  • .043" (1.1mm): Extremely narrow. Used exclusively on small pole pruners and entry-level battery/electric saws (and the Stihl MS170/180 series).

  • .050" (1.3mm): The global standard. Used by Stihl, Husqvarna, and Oregon on 80% of chainsaws worldwide.

  • .058" (1.5mm): A legacy size often found on Husqvarna and Jonsered saws. Visually identical to .050, causing frequent confusion.

  • .063" (1.6mm): Heavy duty. Used almost exclusively by Stihl on their professional "Farm Boss" and Forestry saws.

The Consequences of Error:

  • Too Thin: Putting an .050" chain in an .058" or .063" bar allows the chain to lean side-to-side. This results in crooked cutting and rapid wear of the bar rails.

  • Too Thick: Putting an .058" chain in an .050" bar will bind immediately. It will likely seize the nose sprocket and burn the bar tip.

3. Drive Links: The Only True Length

Definition: The Drive Link Count (DL) is the total number of drive links in the loop.

This is the only accurate way to communicate length. "18 inches" is a marketing term; "68 Drive Links" is an engineering specification.

How to Count Correctly:

  1. Remove the chain from the saw.

  2. Mark one drive link with a permanent marker or a piece of tape (this is your "Zero").

  3. Count the Drive Links (the inner teeth), not the cutters (the top teeth).

  4. Continue until you reach your mark.

Why Counts Vary:

Different chainsaw manufacturers place the mounting studs (where the bar bolts on) at different distances from the drive sprocket.

  • A Stihl 18-inch bar typically takes 68 Drive Links (.063 gauge).

  • A Husqvarna 18-inch bar typically takes 72 Drive Links (.058 gauge).

  • An Echo 18-inch bar might take 70 Drive Links.

If you order a "Standard 72 link chain" for your Stihl, it will be 4 links too long, and your tensioner will max out before the chain is tight.

Summary: The Identification Hierarchy

When ordering replacement chains from Alpine Chain Co, the hierarchy of accuracy is:

  1. Best: Check the stamp on your old chain's drive link (e.g., Stihl "36" or Oregon "73").

  2. Better: Measure with calipers using the methods above.

  3. Good: Check the stamp printed on the tail of your guide bar.

  4. Risky: Guessing based on "Bar Length."

Ready to find your match?

Now that you know your numbers, use our filters to find the exact Medium-Hard alloy chain for your setup.

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