How to Measure and Identify Your 18 Inch Chainsaw Chain Size (Pitch, Gauge, and Drive Links)? | Three Numbers That Fit

An 18-inch bar tells you almost nothing on its own — the chain must match pitch, gauge, and drive-link count, and all three are stamped on the bar or chain.

A chain that looks right can still bind in the groove or jump the sprocket, and the reason is almost always one of those three numbers. Bar length measures tip reach, not loop length. STIHL defines chain length by drive-link count, and a 60-link 3/8-inch chain and a 62-link.325-inch chain can both ride an 18-inch bar. Getting the numbers off the saw takes about five minutes with the bar in your hand.

Make the Saw Safe and Read the Bar First

Cut the power first. On a gas saw, shut off the engine and pull the spark-plug boot; on a battery saw, remove the pack. Wear gloves — a chain is sharp even when it’s dull enough to replace.

Then go to the guide bar. STIHL stamps the required drive-link count into the bar tail, near where the bar mounts to the powerhead. Many bars also carry pitch and groove width in the same service field. If the markings are worn, a parts diagram for your exact model will list the stock bar and chain combination.

Identify Pitch, Gauge, and Drive-Link Count

Pitch is the distance between the centers of three consecutive rivets, divided by two. Three rivets measuring 0.750 inch apart gives 3/8-inch pitch; a.325-inch chain measures about 0.650 inch. Pitch is not cutter spacing or bar length, and the chain, bar, and drive sprocket must all share it.

Gauge is the thickness of the drive links — the tabs that ride inside the bar groove. STIHL’s common gauges are.043 inch (1.1 mm),.050 inch (1.3 mm),.058 inch (1.5 mm), and.063 inch (1.6 mm). Gauge must match groove width exactly: a thin link wanders, a thick one won’t seat.

Drive-link count is where most people go wrong. Count only the inward-facing tabs that run in the groove — not cutters, tie straps, or rivets. That count sets loop length, which is why two 18-inch chains can carry very different numbers of links.

The Markings Already on Your Chain

The code is a digit: 1 means.043 inch, 3 means.050 inch, 5 means.058 inch, and 6 means.063 inch.

Those stamps are a fast cross-check, not a final answer — especially if the bar or sprocket has been swapped. Verify against the bar and the saw’s specs before you buy.

An 18-inch bar can carry 3/8-inch PICCO, standard 3/8-inch, or.325-inch pitch depending on the bar and sprocket. STIHL’s Sharp Advice guide to saw chain and guide bars lays out the full measurement method to verify any number yourself.

Mistakes That Cost You a Second Order

The most expensive error is assuming every 18-inch chain fits every 18-inch bar. It doesn’t — a single mismatch turns a new chain into a return.

• Confusing.325 inch with 3/8 inch. Different pitches — sprocket, bar, and chain must agree.
• Treating standard 3/8 inch as 3/8-inch PICCO. PICCO is a distinct low-profile family; check the exact bar spec.
• Counting cutters instead of drive links. Cutters tell you nothing about loop length.
• Trusting a worn chain’s stamp alone after a bar or sprocket swap.
• Ignoring kickback. STIHL recommends green-labeled low-kickback chain and reduced-kickback bars where the saw allows, correct tension, and dealer verification when unsure.

Once you have all three numbers, comparing replacements gets simpler — our tested roundup of 18-inch chainsaw chains groups picks by pitch and gauge so you can match your numbers directly.