How to Measure Bar Length on a Chainsaw: Cutting Length & True Bar Length

Why Bar Length Measurement Matters

Getting the bar length wrong is one of the most common and costly mistakes chainsaw owners make when ordering replacement parts. A chain that is even one size off will not seat correctly in the bar groove, creating dangerous slack or excessive tension that can cause the chain to derail mid-cut. At best, a mismatched chain means a wasted purchase and a trip back to the supplier. At worst, it creates a serious safety hazard for the operator.

Bar length also determines what size wood your chainsaw can handle in a single pass. As a general rule, the diameter of the log you are cutting should be no more than two inches less than the bar's cutting length. Trying to cut a 20-inch diameter trunk with a 16-inch bar forces you into multiple repositioning cuts — increasing fatigue and the risk of pinching. Knowing your exact bar length helps you work within the tool's designed capability and maintain full control throughout the cut.

Finally, if you are sourcing a replacement chainsaw guide bar, manufacturers size their bars in standardized increments. Providing an inaccurate measurement means the replacement bar may not mount correctly to your chainsaw's body, since the tail section — the portion that slots into the saw — must match the original precisely.

Cutting Length vs. True Bar Length: Know the Difference

There are two distinct measurements associated with a chainsaw bar, and confusing them is the root cause of most sizing errors. Understanding what each one means — and when to use it — is the foundation of getting the right parts every time.

Cutting length, also called the called length or effective cutting length, is the measurement most users need. It represents the usable portion of the bar — the section of the blade that actually contacts the wood during a cut. This is the number printed on chainsaw packaging and used in product listings. It is always rounded to the nearest even inch.

True bar length is the complete end-to-end physical measurement of the bar, including the tail section that sits inside the chainsaw body. This number is longer than the cutting length and is not rounded. You need the true bar length only in specific situations: when ordering a direct-fit replacement bar from a manufacturer's parts catalog, or when the bar's tail must match a precise slot dimension on the saw's mounting plate.

For the vast majority of purchases — replacement chains, compatible aftermarket bars listed by cutting length, and general size identification — the cutting length is all you need.

How to Measure Cutting Length (Step by Step)

This method requires nothing more than a standard tape measure and takes under two minutes. No disassembly is needed.

1. Place the chainsaw on a flat, stable surface. A workbench is ideal. Make sure the saw is switched off, the chain brake is engaged, and the engine is cool before you begin.
2. Locate the tip of the bar. This is the rounded nose at the far end of the guide bar, away from the chainsaw body.
3. Identify the base point. This is the point where the bar disappears into the chainsaw body — specifically, where the bar enters the housing, not where the bar ends inside the saw.
4. Measure from tip to base. Extend the tape measure from the outermost point of the bar's tip straight back to the entry point at the chainsaw body. Keep the tape parallel to the bar's centerline for an accurate reading.
5. Round up to the nearest even number. Chainsaw bars are manufactured and sold only in even-inch sizes. If your tape reads 15.5 inches, your cutting length is 16 inches. If it reads 17.75 inches, the bar is an 18-inch bar. Always round up, never down.

The most common cutting lengths for homeowner and semi-professional use are 14, 16, 18, and 20 inches. Professional and arborist saws commonly run 20 to 28 inches, while specialized harvesting equipment can use bars of 36 inches and above.

How to Find the True Bar Length

You only need this measurement when ordering a direct OEM replacement bar that must match the original part number exactly. The process requires removing the bar from the saw.

1. Disconnect the spark plug lead (gas saws) or remove the battery (battery-powered saws) before handling the bar.
2. Loosen the bar retaining nuts. On most chainsaws, two nuts on the side cover secure the bar and chain to the saw body. Use the correct wrench size — typically a combination bar wrench and scrench supplied with the saw.
3. Remove the side cover and slide the bar free. The bar will slide off the mounting studs once the cover is removed. Set the chain aside carefully on a clean surface. If you need to inspect or replace the replacement sprocket nose at the tip of the bar, this is the right moment to do so.
4. Lay the bar on a flat surface and measure end to end. Place the tape at one end of the bar and extend it to the opposite end. Record this measurement precisely — do not round it.

Write this number down along with the cutting length and keep both measurements with your chainsaw manual. Having both figures on hand eliminates guesswork for every future parts purchase.

Reading the Bar Label Instead of Measuring

In many cases, you can skip the tape measure entirely. Most guide bars have their specifications stamped or printed directly onto the metal, typically on the flat side of the bar near the tail — the section closest to the chainsaw body.

Look for a series of numbers in this area. You may find the cutting length in inches, the bar's pitch and gauge specifications, or a part number that cross-references directly to the manufacturer's catalog. On bars that have seen heavy use, this printing can be worn or obscured by oil and sawdust. A rag dampened with a small amount of solvent will usually reveal the text clearly.

If the label is unreadable and disassembly is not practical, the cutting length measurement method described above will always give you the number you need. The label is a convenience, not a requirement.

Matching Bar Length to the Right Chain

Once you have your cutting length, you are halfway to selecting the correct chainsaw chain. Bar length alone is not enough to specify a chain — you also need three additional measurements: pitch, gauge, and drive link count.

Pitch is the distance between any three consecutive rivets on the chain divided by two. Common values are 1/4", 3/8" low-profile, 3/8", and .325". The pitch of the replacement chain must exactly match the pitch of the drive sprocket on your saw and the sprocket nose on the bar.

Gauge refers to the thickness of the drive links — the fins on the inside of the chain that ride in the bar groove. Common gauges are .043", .050", .058", and .063". A chain with the wrong gauge will either rattle loosely in the groove or refuse to fit at all. You can measure gauge with a dial caliper, or use the coin approximation method: a penny approximates .043", a dime approximates .058", and a quarter approximates .063".

Drive link count is the total number of drive links around the entire chain loop. Two chains can share the same pitch, gauge, and cutting length but have different drive link counts depending on how the bar was designed. Count the links on your current chain by laying it flat and counting each drive link around the full loop. This number, combined with pitch and gauge, uniquely identifies the correct replacement chain for your specific bar and saw combination.

These are general reference values only. Always verify pitch, gauge, and drive link count against your specific saw model before ordering.

Common Measurement Mistakes to Avoid

Even experienced users make avoidable errors when measuring chainsaw bar length. Here are the four most frequent problems and how to prevent them.

Measuring the entire bar instead of the cutting length. Many people instinctively measure the bar end to end while it is still mounted on the saw, which gives the true bar length rather than the cutting length. The result is a number that does not correspond to any standard product size. Use the tip-to-body method for cutting length, or remove the bar for true bar length — never combine the two.

Rounding down instead of up. Because bars are only made in even-inch sizes, any fractional measurement must always round upward to the next even number. Rounding a 17.5-inch measurement down to 16 inches will result in a chain that is too short and dangerously tight on the bar.

Assuming bar length is enough to buy a chain. As described in the previous section, pitch, gauge, and drive link count are all required to specify a chain correctly. Bar length only tells you the loop size in general terms. Two bars of the same cutting length from different manufacturers can require very different chains.

Ignoring wear on a used bar. A heavily used bar may have developed a slight curve or uneven wear at the tip, which causes tape measurements to read slightly short. If your measurement seems unexpectedly low compared to what you recall, check the bar tip for wear and consider whether the bar itself needs replacement before a new chain is ordered.